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Padlet created by our students of radio telescopes around the world

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Padlet created by our students of radio telescopes around the world

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Students investigated different radio telescopes around the world and dropped a pin on their location using Padlet. For each radio telescope found they added the website for people to be able to find out more about the telescope. The map allowed students to zoom right in and see where the radio telescopes were located and how they are in quiet regions which are "radio quiet" i.e. low RFI.

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Activity where students investigated the different frequencies emitted by car key fobs using software defined radio.

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Building a simple Kepler telescope activity sheet

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Building a simple Kepler telescope activity sheet

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This activity allows students to build a simple Kepler style telescope. Students get to put their optics knowledge into action.

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Great educational resources from I-LOFAR.
Lovely activity where students have to put images in order of when they were taken to show the advancement of telescopes through the ages.

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The telescope is one of humankind's most important inventions, although we're not entirely sure who to give the credit to.

The first person to apply for a patent for a telescope was Dutch eyeglass maker Hans Lippershey (or Lipperhey). In 1608, Lippershey laid claim to a device that could magnify objects three times. His telescope had a concave eyepiece aligned with a convex objective lens. One story goes that he got the idea for his design after observing two children in his shop holding up two lenses that made a distant weather vane appear close. Others claimed at the time that he stole the design from another eyeglass maker, Zacharias Jansen.
Related: Best telescopes 2021: Top picks for viewing planets, stars, and more
Jansen and Lippershey lived in the same town and both worked on making optical instruments. Scholars generally argue, however, that there is no real evidence that Lippershey did not develop his telescope independently. Lippershey, therefore, gets the credit for the telescope, because of the patent application, while Jansen is credited with inventing the compound microscope. Both appear to have contributed to the development of both instruments.

Adding to the confusion, yet another Dutchman, Jacob Metius, applied for a patent for a telescope a few weeks after Lippershey. The government of the Netherlands turned down both applications because of the counterclaims. Also, officials said the device was easy to reproduce, making it difficult to patent. In the end, Metius got a small reward, but the government paid Lippershey a handsome fee to make copies of his telescope.

Galileo's telescope

In 1609, Galileo Galilei heard about the "Dutch perspective glasses" and within days had designed one of his own - without ever seeing one. He made some improvements - his creation could magnify objects 20 times - and presented his device to the Venetian Senate. The Senate, in turn, set him up for life as a lecturer at the University of Padua and doubled his salary, according to Stillman Drake in his book " Galileo at Work: His Scientific Biography" (Courier Dover Publications, 2003).

Galileo was the first to point a telescope skyward. He was able to make out mountains and craters on the moon, as well as a ribbon of diffuse light arching across the sky - the Milky Way. He also discovered the rings of , sunspots and four of Jupiter's moons.

Thomas Harriot, a British ethnographer and mathematician, also used a spyglass to observe the moon. Harriot became famous for his travels to the early settlements in Virginia to detail resources there. His August 1609 drawings of the moon predate Galileo's, but were never published.

The more Galileo looked, the more he was convinced of the sun-centered Copernican model of the planets. Galileo wrote a book " Dialogue Concerning the Two Chief World Systems, Ptolemaic and Copernican" and dedicated it to the Pope Urban VIII. But his ideas were considered heretical, and Galileo was called to appear before the inquisition in Rome in 1633. He struck a plea bargain and was sentenced to house arrest, where he continued to work and write until his death in 1642.
Related: The Daniel K. Inouye Solar Telescope: Getting a close-up look at our sun
Elsewhere in Europe, scientists began improving the telescope. Johannes Kepler studied the optics and designed a telescope with two convex lenses, which made the images appear upside down. Working from Kepler's writings, Isaac Newton reasoned it was better to make a telescope out of mirrors rather than lenses and built a reflecting telescope in 1668. Centuries later the reflecting telescope would dominate astronomy.

Exploring the cosmos

The largest refracting telescope (one that use lenses to gather and focus light) opened at Yerkes Observatory in Williams Bay, Wisconsin, in 1897. But the 40-inch (1 meter) glass lens at Yerkes was soon made obsolete by larger mirrors. The Hooker 100-inch (2.5 m) reflecting telescope opened in 1917 at Mount Wilson Observatory in Pasadena, Calif. It was there that the astronomer Edwin Hubble determined that the Andromeda Nebula was indeed (as some astronomers had argued) a galaxy far, far away (2.5 million light-years) from the Milky Way.

With the development of the radio, scientists could start to study not just light, but other electromagnetic radiation in space. An American engineer named Karl Jansky was the first to detect radio radiation from space in 1931. He found a source of radio interference from the center of the Milky Way. Radio telescopes have since mapped the shape of galaxies and the existence of background microwave radiation that confirmed a prediction in the Big Bang Theory.

Famous telescopes

Here are some of the more famous telescopes:

This is the successor to Hubble, and its launch date has been delayed several times over the years, with the latest estimate now for Dec 18, 2021. Unlike Hubble, this telescope will be parked far from Earth and out of reach of repair crews. Its science will look at four major themes: the universe's first light, how the first galaxies were formed, how stars are formed, and looking at the origins of life (including exoplanets).

This telescope launched in 1990. Some of Hubble's major contributions include determining the age of the universe with more precision, finding more moons near Pluto, doing observations of galaxies in the young universe, monitoring space weather on the outer planets, and even observing exoplanets - a situation not anticipated for the telescope as the first major exoplanet discoveries didn't happen until the mid-1990s.

A flaw in its mirror was fixed with an upgrade from a space shuttle crew in 1993. Hubble underwent five servicing missions by shuttle crews, with the last one being in 2009. It remains in good health to this day and is expected to overlap some observations with the James Webb Space Telescope (Hubble is part of a set of four "great observatories" launched by NASA in the 1990s and 2000s. The other members included the Spitzer Space Telescope, the Compton Gamma Ray Observatory and the Chandra X-Ray Observatory, which made many discoveries of their own.)

This planet-hunting machine has found more than 4,000 potential planets since first launching in 2009. Initially, it focused on a section of the Cygnus constellation, but in 2013 problems with pointing consistently created a new mission in which Kepler moves between different regions of the sky. One of Kepler's major contributions is finding more super-Earths and rocky planets, which are harder to spot near bright stars.

This telescope in Chile has 66 receivers and its specialty is looking through the dust in young planetary systems (or through dusty stars and galaxies) to see how cosmic objects are formed. It was fully operational as of 2013. ALMA is unique in its sensitivity because it has so many receivers available. Some of its results include the clearest-ever image of the star Betelgeuse, and precise measurements of black hole masses.

This observatory began operating since 1963, and is famous for many radio astronomy studies. The Puerto Rican telescope is also know for a message called the Arecibo Message that was directed at the globular cluster M13 in 1974. The observatory was damaged during a 2017 hurricane that devastated Puerto Rico. In popular culture, Arecibo was also the location of the climax of the 1995 James Bond film "Goldeneye", and it appeared in the 1997 movie "Contact."

On Dec. 1, 2020, the Arecibo Observatory collapsed due to structural failure and was deemed too costly to repair. The remaining structure was dismantled.

This is a set of 27 telescopes located in the New Mexico desert. Construction began on the VLA in 1973. Some of the VLA's major discoveries include finding ice on Mercury, peering into the dusty center of the Milky Way, and looking at the formation of black holes. The telescope array also was prominently featured in the 1997 movie "Contact" as the site where a purported extraterrestrial signal arrived.

The twin telescopes at the W.M. Keck Observatory in Hawaii are the largest optical and infrared telescopes available. The telescopes started their work in 1993 and 1996. Some of their major discoveries including finding the first exoplanet "transiting" across its parent star, and learning about star movements in the nearby Andromeda Galaxy.
Additional reporting by Elizabeth Howell, Space.com contributor
The Palomar Observatory, located in San Diego County, Calif., began work in 1949. The telescope is best known for discovering the small worlds Quaoar, Sedna and Eris in the Kuiper Belt, but its work also includes discovering supernovas (star explosions), tracking asteroids and looking at gamma-ray bursts.

Additional resources

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Several men laid claim to inventing the telescope, but the credit usually goes to Hans Lippershey, a Dutch lensmaker, in 1608.

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Learn about Lord Rosse's Birr Leviathan telescope and its various important discoveries, the most important being the detailed observations of many nebulae at Birr Castle, Ireland University College Cork, Ireland (A Britannica Publishing Partner)

So here we are, anyway, in Birr Castle, which is the location of one of the great scientific marvels of Ireland, the so-called Birr Leviathan, which for about 70 years was the largest telescope in the world, with which several important discoveries were made by its creator, Lord Ross. The telescope has a mirror-- an aluminum mirror-- with a diameter about 6 feet, which for its time was an absolutely enormous undertaking, which Lord Ross undertook with great success. And also, the support of the mirror, because it was so large, had to be very carefully engineered, too. And that was designed by Thomas Grubb, whose son became the very famous telescope maker, Howard Grubb.

And so the mirror of the Birr Leviathan, the 6-foot aluminum mirror, because it's so heavy, one has to be very careful to keep it in the correct shape to get the best images from the stars. And the task of engineering that fell to Thomas Grubb, who was the father of Howard Grubb, who designed and built all of the instruments in the Crawford Observatory in University College Cork.

Lord Ross was a very creative and highly successful inventor of telescopic apparatus. And the Leviathan is his crowning achievement. Because of the size of it, it couldn't really be pointed very easily in the sky. And so it was limited to pointing at objects that pass very near the meridian, the line that passes through the North Pole, the zenith, and the South Pole.

But even despite that, several very important discoveries were made. The most important discovery, and the one for which he's most famous, was his very detailed observations of many nebulae-- which, at the time, people weren't sure if these were gas clouds, or maybe consisted of a greater population of stars. And his observations gave very strong evidence that in fact, these nebulae-- some of these distant nebulae consisted of many, many stars, which he could resolve with his telescope for the first time.

And he sketched many of these galaxies. His most famous is his M51, the Whirlpool Galaxy. And even today, when you compare his sketches to images taken by the Hubble Space Telescope, they are remarkably true to the original galaxy. And so his observations are really the first that shows that the galaxy we live in, the Milky Way, is not the only galaxy in the universe, and in fact, there are many thousands and millions of galaxies like it distributed across the universe. And his observations were the first to shine light on that very important location of ourselves in the universe at large.

He made many other important measurements. One that was particularly dear to his heart was measuring the temperature of the moon. And to do this, he used one of the other telescopes he had made here, a 3-foot telescope, and at the end of which traced detectors called thermocouples, which could be used to actually measure the radiation from the moon very accurately.

He realized that really, to do this as best as possible, he needed to do it in the infrared. And so he tried to deal with various technical issues that arise because of that, including trying to control the background. Because the background radiation can be very high in the infrared, just due to emission from the telescope itself, and from other sources, too. So he was one of the very first infrared astronomers. And he'd be particularly interested in things like the James Webb Space Telescope, when it's launched in a few years' time, because that will be almost exclusively working in infrared wavelengths, too.

Initially, his temperature was quite a bit off, unfortunately. But about 100 years later, somebody took his original data and re-reduced them and compared them to a better model. And what they found was that the original data were actually excellent, but the way he interpreted the data was not as good as he could have expected. And the person who re-analyzed Lord Ross's data showed that in fact, the temperature he would have got of the moon was almost exactly the correct one, if he had a slightly better understanding of how to analyze the data.

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Learn about Lord Rosse's Birr Leviathan telescope and its various important discoveries, the most important being the detailed observations of many nebulae at Birr Castle, Ireland

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So here we are, anyway, in Birr Castle, which is the location of one of the great scientific marvels of Ireland, the so-called Birr Leviathan, which for about 70 years was the largest telescope in the world, with which several important discoveries were made by its creator, Lord Ross.

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This activity gets students to investigate radio frequency interference from electronic devices and how RFI is a problem for radio astronomy.

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Really nice video to show students all the different types of electromagnetic waves being emitted all around us.

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Video on RFI and the VLA (Very Large Array)

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Video on RFI and the VLA (Very Large Array)

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Lovely short video to show students how RFI interferes with radio astronomy.

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The National Radio Astronomy Observatory NRAO

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Radio Frequency Interference (RFI) and You

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Video to start a discussion with students on other objects that cause interference in the sky.

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Lunar Crater Radio Telescope (LCRT) on the Far-Side of the Moon

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Lunar Crater Radio Telescope (LCRT) on the Far-Side of the Moon

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Great educational resources on what happens in I-LOFAR and why it is located in Birr in Ireland. PDFs and PPTs to use in class.

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The focus of this lesson and activity is to give students an introduction to the world of radio astronomy and specifically in an Irish context. It gives an opportunity to understand the electromagnetic spectrum, radio frequency interference and the process in which radio frequencies can be studied. This is done through an investigation of I-LOFAR and how it connects to the larger International LOFAR Telescope network.
Background information
Radio astronomy is the observation of radio frequencies from space in order to understand different celestial bodies and phenomena. Radio waves are a type of light, or electromagnetic radiation that make up a portion of the electromagnetic spectrum. Other types of radiation you may have heard of include infra-red, ultraviolet and x-rays as well as visible light. By collecting all different forms of radiation we can reveal things that could not be seen in visible light and gain a clearer understanding of outer space.

Radio frequency interference (RFI) is very important to consider in radio astronomy. Like light pollution can hinder looking at the stars, RFI can hinder collecting radio frequencies. Not only is it necessary to avoid areas with a lot of interference from radio stations but also lots of electrical equipment and devices can give off RFI. There are maps to look at where the least RFI occurs and this is why Birr was chosen for the I-LOFAR radio telescope.

Not only was Birr chosen because of its low RFI, the area also contains history of Ireland's past astronomy accomplishments such as the Leviathan Telescope which we cover in our ' Telescopes through the Ages ' lesson. I-LOFAR also offers the opportunity of STEM to the midlands that are underserved by 3rd level institutions and tends to have less uptake in those areas of study.

The radio telescope itself is not what you might imagine a typical telescope or radio dish to look like. It is made up of two types of antennae observing frequencies above and below regular FM radio, high band and low band antennas. These antennae can be focused on particular areas of the sky using interferometry as delays between antennae show where a signal is coming from. Radio waves can be collected all day, everyday giving us a lot of data to sort through. You can see some of the collected data . The data is used by scientists to explore many different topics such as solar weather and the first light in the Universe.

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The focus of this lesson and activity is to give students an introduction to the world of radio astronomy and specifically in an Irish context. It gives an opportunity to understand the electromagnetic spectrum, radio frequency interference and the process in which radio frequencies can be studied.

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National Geographic article on Green Bank Telescope and National Radio Quiet Zone.

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Life in the Quiet Zone: West Virginia Town Avoids Electronics for Science

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Neighbors of giant radio telescope in West Virginia give up wireless gadgets so astronomers can hear the music of the spheres.

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Neutral Hydrogen Line using Pictor Radio Telescope activity sheet

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Neutral Hydrogen Line using Pictor Radio Telescope activity sheet

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This activity allows students to use a radio telescope based in Athens, Greece to search for the 21 cm hydrogen line in the sky. They can also check for red/blue shift.

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Free for students and educators to use. Very quick and raw data and graphs are emailed to you within 5 minutes of use.

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PICTOR, located in Athens, Greece, consists of a 1.5-meter parabolic antenna that allows anyone to make continuous and spectral (i.e. hydrogen line) drift-scan observations of the radio sky in the 1300~1700 MHz regime for free.

The goal of this effort is to introduce students, educators, astronomers and others to the majesty of the radio sky, promoting radio astronomy education, without the need of building a large and expensive antenna.

PICTOR is a fully open source (software & hardware) project: https://github.com/0xCoto/PICTOR

Telescope diameter: 1.5m (4.92 ft = 59.05")
Focal Ratio (F/D): 0.411 (prime focus antenna)
Beamwidth (HPBW @ 1420 MHz): ~8.95° ( k factor = 63.64)
Operating frequency range: 1300~1700 MHz ( L band)
Two-stage low-noise amplifier (LNA): Gain: 30 ± 2 dB - Noise figure (NF): < 0.5 dB
High-pass filter: -30 dBc below 900 MHz
Third-stage LNA (used as an in-line amplifier): Gain: > 9 dB *
Band-pass filter: f_center = 1420 MHz (designed for hydrogen line observations) *
Instantaneous bandwidth (IBW): up to 3.2 MHz (sufficient for spectral observations) [to be upgraded to 30.72 MHz]
Number of channels: up to 2048 (for high frequency-resolution observations) [to be upgraded to 16384]
* Deemed unnecessary hence removed

Take a look at the PDF guide (available in English and Greek) containing all the information you need to know in order to conduct your first observation of the radio sky!

Ready to explore the radio sky?

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PICTOR, located in Athens, Greece, consists of a 1.5-meter parabolic antenna that allows anyone to make continuous and spectral (i.e. hydrogen line) drift-scan observations of the radio sky in the 1300~1700 MHz regime for free.

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Free to use astronomy software to see what is in the sky

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Stellarium is a free open source planetarium for your computer. It shows a realistic sky in 3D, just like what you see with the naked eye, binoculars or a telescope.

features

sky

default catalogue of over 600,000 stars

extra catalogues with more than 177 million stars

default catalogue of over 80,000 deep-sky objects

extra catalogue with more than 1 million deep-sky objects

asterisms and illustrations of the constellations

constellations for 40+ different cultures

calendars of 35+ different cultures

images of nebulae (full Messier catalogue)

realistic Milky Way

very realistic atmosphere, sunrise and sunset

the planets and their satellites

all-sky surveys (DSS, HiPS)

interface

a powerful zoom

time control

multilingual interface

scripting interface

fisheye projection for planetarium domes

spheric mirror projection for your own low-cost dome

graphical interface and extensive keyboard control

HTTP interface (web-based control, remote control API)

telescope control

visualisation

several coordinate grids

precession circles

star twinkling

shooting stars

tails of comets

eclipse simulation

supernovae and novae simulation

exoplanet locations

ocular view simulation

3D sceneries

skinnable landscapes with spheric panorama projection

customizability

plugin system adding artifical satellites, ocular simulation, telescope control and more

ability to add new solar system objects from online resources...

add your own deep sky objects, landscapes, constellation images, scripts...

presentations

news

system requirements

minimal

Linux/Unix; Windows 7 and above; macOS 10.15 and above

3D graphics card which supports OpenGL 2.1 and GLSL 1.3 or OpenGL ES 2.0

512 MiB RAM

600 MiB on disk

Keyboard

Mouse, Touchpad or similar pointing device

recommended

64-bit operating system

Linux/Unix; Windows 10 and above; macOS 11.0 and above

3D graphics card which supports OpenGL 3.3 and above

1 GiB RAM or more

1.5 GiB on disk

Keyboard

Mouse, Touchpad or similar pointing device

Moderately dark environment (deep shadow or indoors)

developers

Project coordinator: Fabien Chéreau
Graphic designer: Martín Bernardi
Developers: Alexander V. Wolf, Georg Zotti, Guillaume Chéreau, Ruslan Kabatsayev, Worachate Boonplod
Sky cultures researcher: Susanne M. Hoffmann
Collaborators: Jocelyn Girod and everyone else in the community.

financial support

Many individuals and organizations are supporting the development of Stellarium by donations, and the most generous financial contributors (with donations of $250 or more) are Laurence Holt, Astronomie-Werkstatt "Sterne ohne Grenzen", John Bellora, Jeff Moe (Spacecruft), BairesDev, Vernon Hermsen, Triplebyte, Marla Pinaire, Satish Mallesh, Vlad Magdalin, Philippe Renoux, Fito Martin.

silver sponsor

social media

collaborate

You can learn more about Stellarium, get support and help the project from these links:

acknowledgment

If the Stellarium planetarium was helpful for your research work, please cite the following paper in your acknowledgment:
This research has made use of the Stellarium planetarium

Zotti, G., Hoffmann, S. M., Wolf, A., Chéreau, F., & Chéreau, G. (2021). The Simulated Sky: Stellarium for Cultural Astronomy Research. Journal of Skyscape Archaeology, 6(2), 221-258. https://doi.org/10.1558/jsa.17822

Or you may download the BibTeX file of the paper to create another citation format.

Please note that the software has several releases since these fundamentals were published:

git

The latest development snapshot of Stellarium is kept on github. If you want to compile development versions of Stellarium, this is the place to get the source code.

books

Documentation and description of the sky cultures, state March 2022, plus a lot of additional research:

supporters and friends

Stellarium is produced by the efforts of the developer team, with the help and support of the following people and organisations .

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Stellarium is a planetarium software that shows exactly what you see when you look up at the stars. It's easy to use, and free.

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3 minute guide on the 21 cm line and CMB.

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Signals from the cosmic dawn: A three minute guide

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Video First detection of hydrogen line by Ewen and Purcell, Harvard, 1951

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Video First detection of hydrogen line by Ewen and Purcell, Harvard, 1951

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Harvard University Detection of galactic hydrogen in 1951 with Doc Ewen & Ed Purcell

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The hydrogen in our galaxy has been mapped by the observation of the 21-cm wavelength line of hydrogen gas. At 1420 MHz, this radiation from hydrogen penetrates the dust clouds and gives us a more complete map of the hydrogen than that of the stars themselves since their visible light won’t penetra…

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Impacts of large satellite constellations

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Impacts of large satellite constellations

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Jason Report on the Impacts of Large Satellite Constellations

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The U.S. National Science Foundation commissioned a study by the independent science advisory group JASON to assess the impact of current and planned large satellite constellations on astronomical observations in 2020. The charge for JASON was to: Understand the types and numbers of spacecraft planned for launch in the next decade.

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Build an Itty Bitty Radio Telescope activity sheet

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Build an Itty Bitty Radio Telescope activity sheet

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This was the first radio telescope we built with our students. It is a very cheap radio telescope to build if you use zero waste means to get your satellite dish with coaxial cable and LNB still attached. It is very simple in its use with a signal finder and allows you to "hear" the detection of radio waves from the sun.

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Video Karl Jansky's discovery of radio signals from space

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Video Karl Jansky's discovery of radio signals from space

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Cool Astronomy Person of the Week: Karl Jansky

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Video How radio telescopes show us unseen galaxies

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Video How radio telescopes show us unseen galaxies

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15 min Ted talk on radio telescopes.

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How radio telescopes show us unseen galaxies | Natasha Hurley-Walker

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Background information on detecting radio waves.

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WHAT ARE RADIO WAVES?

Radio waves have the longest wavelengths in the electromagnetic spectrum. They range from the length of a football to larger than our planet. Heinrich Hertz proved the existence of radio waves in the late 1880s. He used a spark gap attached to an induction coil and a separate spark gap on a receiving antenna. When waves created by the sparks of the coil transmitter were picked up by the receiving antenna, sparks would jump its gap as well. Hertz showed in his experiments that these signals possessed all the properties of electromagnetic waves.

You can tune a radio to a specific wavelength-or frequency-and listen to your favorite music. The radio "receives" these electromagnetic radio waves and converts them to mechanical vibrations in the speaker to create the sound waves you can hear.

RADIO EMISSIONS IN THE SOLAR SYSTEM

Astronomical objects that have a changing magnetic field can produce radio waves. The radio astronomy instrument called WAVES on the WIND spacecraft recorded a day of bursts of radio waves from the Sun's corona and planets in our solar system.

Data pictured below show emissions from a variety of sources including radio bursts from the Sun, the Earth, and even from Jupiter's ionosphere whose wavelengths measure about fifteen meters in length. The far right of this graph shows radio bursts from the Sun caused by electrons that have been ejected into space during solar flares moving at 20% of the speed of light.

RADIO TELESCOPES

Radio telescopes look toward the heavens to view planets, comets, giant clouds of gas and dust, stars, and galaxies. By studying the radio waves originating from these sources, astronomers can learn about their composition, structure, and motion. Radio astronomy has the advantage that sunlight, clouds, and rain do not affect observations.

Since radio waves are longer than optical waves, radio telescopes are made differently than the telescopes used for visible light. Radio telescopes must be physically larger than an optical telescopes in order to make images of comparable resolution. But they can be made lighter with millions of small holes cut through the dish since the long radio waves are too big to "see" them. The Parkes radio telescope, which has a dish 64 meters wide, cannot yield an image any clearer than a small backyard optical telescope!

A VERY LARGE TELESCOPE

In order to make a clearer, or higher resolution, radio image, radio astronomers often combine several smaller telescopes, or receiving dishes, into an array. Together, these dishes can act as one large telescope whose resolution is set by the maximum size of the area. The National Radio Astronomy Observatory's Very Large Array (VLA) radio telescope in New Mexico is one of the world's premier astronomical radio observatories. The VLA consists of 27 antennas arranged in a huge "Y" pattern up to 36 km across (roughly one-and-one-half times the size of Washington, DC).

The techniques used in radio astronomy at long wavelengths can sometimes be applied at the shorter end of the radio spectrum-the microwave portion. The VLA image below captured 21-centimeter energy emissions around a black hole in the lower right and magnetic field lines pulling gas around in the upper left.

THE RADIO SKY

If we were to look at the sky with a radio telescope tuned to 408 MHz, the sky would appear radically different from what we see in visible light. Instead of seeing point-like stars, we would see distant pulsars, star-forming regions, and supernova remnants would dominate the night sky.

Radio telescopes can also detect quasars. The term quasar is short for quasi-stellar radio source. The name comes from the fact that the first quasars identified emit mostly radio energy and look much like stars. Quasars are very energetic, with some emitting 1,000 times as much energy as the entire Milky Way. However, most quasars are blocked from view in visible light by dust in their surrounding galaxies.

Astronomers identified the quasars with the help of radio data from the VLA radio telescope because many galaxies with quasars appear bright when viewed with radio telescopes. In the false-color image below, infrared data from the Spitzer space telescope is colored both blue and green, and radio data from the VLA telescope is shown in red. The quasar-bearing galaxy stands out in yellow because it emits both infrared and radio light.

Top of Page | Next: Microwaves

Citation

APA

National Aeronautics and Space Administration, Science Mission Directorate. (2010). Radio Waves. Retrieved [insert date - e.g. August 10, 2016], from NASA Science website: http://science.nasa.gov/ems/05_radiowaves

MLA

Science Mission Directorate. "Radio Waves" NASA Science. 2010. National Aeronautics and Space Administration. [insert date - e.g. 10 Aug. 2016] http://science.nasa.gov/ems/05_radiowaves

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WHAT ARE RADIO WAVES? In 1932, Karl Jansky at Bell Labs revealed that stars and other objects in space radiated radio waves. Credit: NRAO/AUI Radio waves have the longest wavelengths in the electromagnetic spectrum. They range from the length of a football to larger than our planet.

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How to build a simple radio telescope | Understand the far off universe under $15!

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Part of FOSDEM conference 2020

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PICTOR: A free-to-use open source radio telescope

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Dimensions used for the pyramidal horn side 1

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Dimensions used for the pyramidal horn side 1

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Dimensions used for pyramidal horn side 2

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Dimensions used for pyramidal horn side 2

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Further detailed instructions which were used as a guideline

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Further detailed instructions which were used as a guideline

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Read the stories from our teams, as they progressed through each of their own projects. Each story will be listed below in chronological order of its arrival.
ANNOUNCEMENT
COVID-19 UPDATE: Due to the COVID-19 virus outbreak, our teams have not been able to complete their projects since June 2020, and as such - their information is not yet available. We will provide this information once the teams are back into building their telescopes and have outlined their journey / results .
To keep up to date of when this happens, and the latest information about this project - please follow our project on our @SpaceAusDotCom Twitter or Instagram, under the hashtag #SpaceAusScope. Date: 15 January 2021
Team: Kent Rogers
Project Stage: Completed
The following post has been supplied by Kent Rogers from Melbourne and has been replicated with permissions. All images have been supplied by Mr Rogers and approved for usage.

A Wheelie Bin Radio Telescope!

by Kent Rogers

Having a passing interest in astronomy and particularly radio astronomy, I had long held the ambition of constructing my own backyard radio telescope. For many decades, this seemed a task requiring a level of commitment beyond what I was willing or able to devote. In 2020, finding myself recently retired and looking for a project during Covid 19 lockdown, I again looked at the possibility of undertaking this task. A search of the internet revealed a number of articles about building backyard radio telescopes. What's more advances in microelectronics over the last ten or more years meant that the required preamps, filters and LNAs were now easily available in ready built affordable packages.

A number of articles [1,2,3,4] caught my attention regarding construction of small horn antennas that seemed relatively easy to construct and held the exciting prospect of being able to detect neutral atomic hydrogen (H1) line radio emissions from the Milky Way. It was one of these backyard radio telescopes that I decided to build. Similar to telescopes described in a number of articles, the scope that I constructed is designed to detect H1 emissions at 21 centimetre wavelengths. The main addition to my telescope is to make it weatherproof by housing it within a 240 litre wheelie bin. The size of a 240 litre wheelie bin enabled all of the horn, waveguide and electronic components to be housed within it with only minimal compromise on the size of the horn and hence gain of the antenna. The size of the bin allowed the horn throat to be 560mm x 510mm with a height of 640mm to the top of the olive oil can waveguide. This resulted in a calculated gain of 17.5dB and a 3dB beamwidth of approximately 27°.

The antenna components are therefore:

240 litre wheelie bin

Horn made from aluminium flashing (0.7mm thick) and tape

Waveguide made from a 4 litre olive oil tin

Antenna made from straightened paperclip soldered to a TV PAL socket

PAL to F and F to SMA adaptors

Nooelec SAWbird+ H1 - Premium SAW Filter & LNA for H1 Line (21cm) applications.

Nooelec NESDR Smart v4 SDR Premium

20 metre USB data cable with inbuilt signal amplifier

PC running Windows 10

SDRSharp v 1.0.0.1732 RTL-SDR (USB) software with IF Average plug in

Stellarium 0.20.2 software

Timber was securely taped to the bottom of the waveguide olive oil tin which then was attached to the base of the wheelie bin by 4 small bolts and the four sides of the horn taped together with flashing tape and taped to both the waveguide and top rim of the wheelie bin. The paper clip antenna was cut to 5.25cm (quarter wavelength) and secured via the socket attached through the wall of the waveguide. The antenna is located 6.75cm from the back wall of the waveguide. This is a quarter of the modified wavelength within the waveguide and is determined by the dimensions of the waveguide. In this case, the waveguide opening of 16.8cm x 10.4cm results in a working wavelength range of 33.66cm to 20.8cm i.e. a bandwidth of 1,114 MHz to 1,693 MHz. The free space hydrogen line wavelength of 21cm is modified to 27cm within this waveguide.

An access hatch with a hinged door was cut in the side of the wheelie bin to enable access to the electronics at its base. A 20m USB cable was run through a slot in the hatch door then under the house to a PC located indoors. I also constructed an altazimuth mount for the telescope. This was a timber construction consisting of a rectangular frame mounted on posts attached to a timber platform with castors (a moving dolly). This enabled the telescope to be rotated both vertically and horizontally.

Figure 1 - Wheelie Bin Telescope. Figure 2. Aluminium Flashing horn. Figure 3 - Oil tin waveguide, LNA and SDR inside the hatch at the base of the Wheelie Bin.

The biggest challenge was setting up the required SDR software on the PC. I tried both HDSDR and SDRSharp and found that SDRSharp was the preferred software once the IF Average plugin was downloaded and installed. This plugin enabled the signal to be averaged over 902,000 samples which successfully extracted the H1 signal from background noise. An online article in RTL-SDR.COM [5] described this software set up as well as running the star map software, Stellarium, at the same time as SDRSharp. Doing this enabled me to locate the Milky Way in relation to the antenna direction even during daylight. Using the galactic grid of Stellarium also meant that it was possible to identify the direction of the signal origin when the Milky Way was in view.

Even though I built an altazimuth mount for my wheelie bin telescope, I initially pointed the telescope straight up at the azimuth and took regular recordings as the Milky Way drifted in and out of range. On first light, I was delighted and amazed to receive strong signals each time the Milky Way drifted into view.

A sequence of fourteen captures was taken from Melbourne, Australia on 31 July 2020 and 1 August 2020 showing the rise and fall of the hydrogen line signal with the telescope pointing at the azimuth. Five of these captures are shown below to illustrate the change in signal as the Milky Way drifts across the field of view.

Figure 4 - Capture 7. Pointing -20-degrees from centre of the Galaxy. Frequency 1420.34 MHz.

Figure 5 - Captire 11. Pointing away from the Milky Way. Frequency 1420.4 MHz.

Figure 6 - Capture 12. Pointing away from the Milky Way - minimal signal.

Figure 7 - Capture 16. Pointing 110-degrees from the centre of the Galaxy. Evidence of 2 signal peaks.

Figure 8 - Capture 17. Poimting 110-degrees from the centre of the Galaxy. Frequency 1420.26 MHz.

Capture 7 is taken with the Milky Way at the azimuth and the telescope pointing just -20° from the centre of the galaxy. The signal frequency is centred on 1420.35 MHz. Captures 11 and 12 show the signal reducing as the Milky Way drifts out of view. The small observable signal is centred on 1420.4 MHz. The signal builds again over Captures 16 to 17 as the Milky Way again moves towards the azimuth; this time with the telescope pointing away from the centre of the galaxy by approximately -110°. A distinct double peak signal can be seen in Capture 16 and the signal frequencies of this double peak are centred on 1420.26 MHz and 1420.34 MHz.

Figure 9 - Map of the Milky Way showing the direction of telescope captures with 27-degree beamwidth.

Figure 9 is a map of the Milky Way showing the direction of the signal source when the Milky Way is at the Azimuth. As noted earlier, Capture 7 is pointing just -20° from the centre of the galaxy bisecting the Sagittarius, Scutum-Centaurus and Norma Arms and then along the length of the Near 3kpc Arm. Captures 16 and 17 are pointing away from the centre of the galaxy by approximately -110° along the end of the Orion Spur and towards the end of the Perseus Arm. The width of the signal source due to the telescope's 27° 3dB beamwidth is also identified on this map. When pointing away from the Milky Way e.g. Captures 11 and 12, the telescope is pointing at an angle above or below the map, i.e. away from the page. For these captures at an angle from the plane of the galaxy, the detected signal will mainly be from H1 in the local area of the Orion Spur rotating in unison with our motion around the centre of the Milky Way. The detected signal is therefore not Doppler shifted from the free space H1 frequency of 1420.4MHz.

Signals from further away will be Doppler shifted if they are originating in different parts of the Milky Way with a non-zero velocity either away from (red shift) or towards (blue shift) Earth. Captures 7, 16 and 17 all resulted in frequencies below the H1 frequency of 1420.4 MHz indicating a red shift i.e. moving away from the Earth. It is possible to speculate on the reason for these red shifts; however this is done with a lack of precision due to the wide beamwidth of the antenna. In the case of Capture 7, the bulk of detected H1 is located towards the edge of the 27° beamwidth within the central bar of the Milky Way.

Apart from near the centre, matter in spiral galaxies orbits the centre at close to a constant velocity regardless of distance from the centre. This departure from Keplerian Rotation is thought to be due to the distribution of dark matter in these galaxies [6]. In the case of the Milky Way the velocity of the Sun and all other objects in the spiral arms has been determined to be between 200 and 240 km/sec. More recent studies have estimated it to be 238 km/sec [7]. Although our galaxy rotates much like a pinwheel, with the stars in the arms of the galaxy orbiting the centre, the rotation of the inner bar is believed to be cylindrical [8]. Because the bulk of the signal in Capture 7 is due to this central bar, the signal source does not significantly contribute to a velocity towards or away from the telescope. The Doppler shift in Capture 7 is therefore almost entirely due to the Sun's velocity away from this source as it orbits the centre of the galaxy. Vector analysis shows this to be approximately 48 km/sec resulting in a red shift of 48 kHz, i.e. a signal of 1420.35 MHz compared with an observed centre frequency of 1420.35 MHz, a remarkable agreement!

The Doppler shifts in Captures 16 and 17 are also due to the relative velocities of the Earth and the signal sources, however in these cases both the velocity of the Solar System and the signal sources contribute to the Doppler shift. The velocity component of the Sun away from the signal sources is approximately 227 km/sec whilst the velocity component towards the Sun of the Orion and Perseus Arms are approximately 173 km/sec and 130 km/sec respectively. The nett velocities are therefore 54 km/sec and 97 km/sec resulting in red shifts of 54 kHz and 97 kHz i.e. signals of 1420.35 MHz and 1420.30 MHz. This compares with measured centre frequencies of 1420.34 MHz and 1420.26 MHz i.e. red shifts of 60 kHz and 140 kHz.

With little more than a wheelie bin, aluminium flashing, an olive oil tin and a paper clip (OK, also some electronics and software) it was possible to detect signals from 20 to 30,000 light years away, including from near the centre of the Milky Way. The agreement between recorded data and theoretical calculations was also remarkable. This exercise has expanded my knowledge of our Galaxy and has given me an existentially profound appreciation of our place within the Universe.
References

1. Open Source Radio Telescopes Projects http://www.opensourceradiotelescopes.org/projects/

2. Implementing a Horn Radio Telescope in HS Physics and Astronomy Digital Signal Processing in Radio Astronomy - a Research Experience for Teachers. John L. Makous, Providence Day School Charlotte, NC https://www.gnuradio.org/grcon/grcon18/presentations/Open_Source_Radio_Telescopes/2-John_Makous-OSRT.pdf

3. Radio Telescopes Horn In With GNU Radio by Al Williams; January 2019 https://hackaday.com/2019/01/20/radio-telescopes-horn-in-with-gnu-radio/

4. Track the Movement of the Milky Way With This DIY Radio Telescope by David Schneider; IEEE Spectrum, September 2019. https://spectrum.ieee.org/geek-life/hands-on/track-the-movement-of-the-milky-way-with-this-diy-radio-telescope

5. Cheap and Easy Hydrogen Line Radio Astronomy with an RTL-SDR, WIFI Parabolic Grid Dish, LNA and SDRSharp; RTL-SDR.COM, January 2020. https://www.rtl-sdr.com/cheap-and-easy-hydrogen-line-radio-astronomy-with-a-rtl-sdr-wifi-parabolic-grid-dish-lna-and-sdrsharp/

6. The Rotation Curve of the Milky Way by Dr. Christopher Palma, Senior Lecturer in the Department of Astronomy and Astrophysics, The Pennsylvania State University; Penn State College of Earth and Mineral Sciences John A. Dutton e-Education Institute: Astro 801 Planets, Stars, Galaxies, and The Universe. https://www.e-education.psu.edu/astro801/content/l8_p8.html

7. Rotation Curve of the Milky Way and the Dark Matter Density by Yoshiaki Sofue. Institute of Astronomy, Graduate School of Sciences, The University of Tokyo, Mitaka, Tokyo; Galaxies, April 2020. https://arxiv.org/abs/2004.11688

8. New Insight into the Bar in the Center of the Milky Way by National Optical Astronomy Observatory, Tucson, Arizona; Astronomy, December, 2011 https://astronomy.com/news/2011/12/new-insight-into-the-bar-in-the-center-of-the-milky-way

Date: 21 May 2020
Team: Space Cadets
Project Stage: Completed
The following post is from Geoff Van Der Wagen's blog, and has been replicated with permission, as are all images from the Geoff's blog. Geoff is part of the Space Cadets team and developed a Heliacal Antenna rather than the horn antennas most teams are building. The blog can be found here: https://thenack.com/2020/05/space-antenna/

Late in 2019 I heard of an upcoming project by SpaceAustralia to home brew your own radio-telescope, with the objective of peering at the Milky Way. Previously only the domain of scientists with very nice radio dishes, the reducing cost of entry has now put it in range of the hobbyist so it seemed like a cool thing to try.

Any given Hydrogen atom floating in space emits a little pulse of radio energy every 10 million years or so, at 1420.4MHz - Wiki. By measuring the strength of the radio wave emissions and the Doppler shift, you can get an idea of the quantity and direction of the Hydrogen.

Space Australia's recommended build was a pyramidal horn antenna, but in the interests of doing something a little different I thought about a Helical antenna. This should be a little easier to build, and the fancy antenna simulation software I have access to at work suggested it might be possible to use a Helical antenna for this task. The biggest challenge is the Hydrogen Line signal is very weak - so weak that thermal noise from the Earth is much noisier (and an antenna needs to be very directional).

The finished antenna

I ended up with a build consisting of an aluminium backplate, a length of 50mm PVC pipe, and some speaker wire wound 20 turns up the outside and hot-glued in place. On the back was a cheap plastic tool box to give some protection to the electronics.

Amplification and signal capture

Off the back of the antenna, the preamp is a NooElec SAWBird+ H1, which is 2 LNA's sandwiching a narrowband filter. This preamp also has a switchable 50 Ohm load, for taking noise calibration measurements. The output is fed to an RTL-SDR.com dongle, with streaming data from the dongle piped through the Raspberry Pi by rtl_tcp and ultimately ending up on my fileserver.

Helical antennas require some impedance matching, which the fancy measuring equipment I have access to at work confirmed was doing the right job. A triangular piece of copper tape converts the 50 ohm feedpoint into the ~120 Ohm characteristic impedance of the antenna.

Impedance matching taper

The rest of the measurements looked good too (helicals are broadband impedance-wise, but their pattern degrades quickly away from design frequency):

Reflection coefficient

Simulated results suggest a fairly clean pattern. In the below plot, the purple circle is 15dB below the main lobe. 20dB would have guaranteed that a hot Earth wouldn't degrade my measurements, this design does get there but only directly behind the antenna. I can expect to see some noise degradation with this build unless my antenna points directly upwards.

At some point, simulations churned out this interesting-looking plot:

I didn't realise finding them would be this easy

Unfortunately my current location doesn't have an unobstructed sky view, the best I could do from our balcony was pointing at 45 degrees elevation into a clear patch of sky. Trees, houses, and our own roof conspired to inject noise from the sides but as a system check it was worth trying out. With the fortune of good weather, the antenna stayed out there for 6 full days. In the end this amounted to 1.5TB of raw data.

After much fiddling with the data, there it was! A quite noticeable bump that appears when the Milky Way core (Sagittarius) passes through the antenna beam, and a smaller bump at lower frequency when the opposite direction (Orion) passes through 12 hours later:

The setup also did look quite photogenic at night:

Not entirely unobsctructed, but good enough!

X marks the spot - 2 satellites crossed paths at just the right time

Pretty cool to still be able to see detail in the core from suburban Sydney.

Date: 7 March
Team: Team Orion
Project Stage: Building Feed-Horns

Team Orion's low cost horn - cardboard, AlFoil and tape.

Today's workshop strategy was to divide and conquer. And that we did.

We went into today deciding to split the team up to build different components of the telescope, which proved to be very efficient. It's good to know that we were able to build on all the theory we did in the last session to hit the ground running.

Ginevra worked on building our low-cost waveguide. For this model, we found a cardboard box that is the appropriate size (i.e. has a broad wall of 16.5cm and a shorter wall of 8.5cm) and we are building a faraday cage to contain the signal - by coating the box with mallable copper sheets.

Cardboard box with copper wire sheets to create a wave guide for the prototype telescope

Whilst Ginevera worked on the wave guide, Naif and Rami finalised the prototype short horn, which we had partially constructed during the last lesson - and put together the big 102cm deep feed horn, made from 5mm thick cardboard, aluminium foil and reflective tape (with some gaffa tape for additional support).

To do this, we first cut out the pieces (see our team page for dimensions) and then covered them with AlFoil that was taped down (no gluing this time). Whilst a few bumps appear in the horn, we think it will be ok to guide the 21cm wave down into the antenna regardless. Best to do this part in an open space, as it requires lots of room to move and flip as you tape and adjust. Minimal three people for this part too.

Lay out all your pieces and line them up

then tape up edges and some support

be sure to use reflective tape on inside of horn

One thing we came across that will be important to future builders is how to structually support the horn (as it is big!) from being floppy. We figured we would build some bamboo shoots (light weight) as a ring around the horn that we slip on and off. We don't want to permanently fix it because it would make getting through doors challenging!

We took both horns (once assembled) outside and stood them up - which gave us a little experimental result ... how does the horn deal with the wind. In both cases, it doesn't! Due to cardboard being rather light and the large surface collecting area/faces, even a slight breeze knocked it about a little. Which told us we need to ensure our mounting in the future is sturdy (and that we should only operate on low-wind days).

When you put the feedhorn by the waveguide (our second model is using an Olive Oil can) the real scale and size of the telescope starts to take shape - and it's impressive!

Side view - note size of waveguide and overall structure

Different angles showing the feedhorn from all sides

Overall, we are really happy with the progress on the horns and are going to commence finalising the olive oil can wave guide and copper box wave guide next week - including connecting our antenna and electronics components - and hopefully acquiring a signal (though, it will not be fine tuned as yet).

Date: 21 February 2020
Team: Team Orion
Project Stage: Electronics Arrive!

Very excited to see the electronic gear arrive. As our team is testing out a couple of models, we ordered (online) the electronics from two organisations:

1. RTL-SDR.com - this whole package cost us about USD $45 and came with a couple of antennas, chords and the LNA. The receiver still has not arrived as it was stuck in China due to Coronavirus supply chain impacts.
2. Nooelec - this package cost us about USD $110 - but also included a bunch of additional items like exrtra cables and bolts.

We can't wait to plug it all in!
Date: 15 February 2020
Team: Team Orion
Project Stage: First Construction!

After purchasing our equipment almost a month back, our calendars didn't align for a quick turnaround of building - but we finally got there.

Our first construction day was both fruitful and frustrating - we thought we had it all mapped out and ready to go in, start cutting things up and then start building.

The reality was, we needed to do some extra thinking and prototyping. In particular, we had to conceptulise the angles and the height of the horns we were building, before we started cutting - so that we would not waste any materials we had purchased.

We tried to figure out the best way to cut the sheets of cardboard - so that each sheet could at least produce two faces of the horn. And to do so, we needed to consider the angles within the trapezium that the horn makes (see our team page for these methods).

In the end we only had one horn cut out and the AlFoil glued on, then we had to wait to let it dry. But it wasn't a loss for us - we needed to go through that thinking process to make sure we understood the dimensions of what we were building properly - to set us up for the next construction session ....

Date: 16 January 2020
Team: Team Orion
Project Stage: Material Shopping
Today was a big day - lots of walking, lots of interesting discussions about our telescopes and lots of new questions that arose from our trip. We set out to visit a amateur radio hobby store in Manly, but before we drove out there - we heard from them that they would not be open today. So we had a morning huddle to change our plans.

Looking at Google Maps, we thankfully were able to work out a solid list of places we wanted to visit for our materials purchases - and it all happened to be in a geographical straight line:

Reject Shop and Artshop at Broadway Shopping Centre

Bunnings in Alexandria

Ikea in Tempe

Spotlight in Rockdale

As part of our objectives, we want to be able to shocase three different telescope models to future builders - highlighting some easy places they can go and find materials and for what costs (and finally the results these produced).

So our first stop was the simple Reject Shop ($2 variety store) where we found a good sized cardboard box for $3. We trotted over to the art shop next to pick up some thin copper sheet for $12. We're going to merge the two and create the waveguide for our first telescope out of a cheap box coated with copper.

Whilst we were at the art shop, we also looked at some firmer cardboard to constuct our feed horn with for our low-cost model (combined with the copper box). The cost of some decent firm cardboard (it needs to be rigid and have a bit of weight for stability and to keep its shape) is $40 for 4 sheets ($10 each). Getting the cardboard to be a feedhorn is easy - we're going to cover it in AlFoil found in our kitchens.

Our next stop, we went to Bunnings to consider the build for our mid-range cost telescope model. It's always so much fun in there - and we spent hours! We looked for Aluminum Flashing material and found out it was called something else - "insulation slverwrap sarkin" or something like that. A 10m roll of this stuff goes for $28.50.

But the Sarkin is really thin, almost paperthin - so we need to give it a backing to build our horn. We looked a range of materials, including:

5mm thick Corflute - which would cost us about $60 for 4 sheets (1200mm x 900mm) - but we decided this was not too far of the cardboard we bought at the art store (in terms of weight, flexibility etc.) so there was no point of going for this

3.2mm Masonite - which would cost us about $60 for 4 sheets (1200mm x 900mm) - but when we picked this up, we thought it was rather heavy - and this triggered questions for us about how we would support the horn on top of the waveguide

3mm Plywood - which would cost us $56 for 4 pieces (1200mm x 810mm) - and this material seemed the best in terms of rigidness vs. weight ... it was not too heavy but strong enough to not be wobbly. Yep, this was what we were going to build our mid-range scope with

For our waveguide, we are going to use a 1ltr Olive Oil can from the supermarket, based on what some other folks have said in the Slack Channel. We are still yet to test the strength and dimensions of this.

Based on our calcs, we need the broadwall of our waveguide to be between 16cm - 17cm. We used 16.5cm broad wall length on the waveguide calculator and it worked out to give us a frequency range of 1.42GHz with exactly 290 MHz (0.29GHz) on either side. That's plenty of bandwidth to cover the central frequency peak we're looking for AND any doppler shift on either side. We're hoping the Olive Oil can can meet this requirement.

We didn't make it to Ikea or Spotlight - but we didn't need to. More shopping on Saturday .... electronics (LNA + receiver) and picking up some odd-ends from Bunnings and the art shop again ....

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Read the stories from our teams, as they progressed through each of their own projects. Each story will be listed below in chronological order of its arrival. ANNOUNCEMENT COVID-19 UPDATE: Due to the COVID-19 virus outbreak, our teams have not been able to complete their projects since June 2020, and as such - their information...

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Video How Penzias and Wilson used a horn antenna to discover cosmic microwave background radiation

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Video How Penzias and Wilson used a horn antenna to discover cosmic microwave background radiation

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How Two Astronomers Accidentally Discovered the Big Bang

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21 cm hydrogen line with a parabolic dish alternative

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21 cm hydrogen line with a parabolic dish alternative

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We've recently been testing methods to help budding amateur radio astronomers get into the hobby cheaply and easily. We have found that a low cost 2.4 GHz 100 cm x 60 cm parabolic WiFi grid antenna, combined with an RTL-SDR and LNA is sufficient to detect the hydrogen line peak and doppler shifts of the galactic plane. This means that you can create backyard hydrogen line radio telescope for less than US$200, with no complicated construction required.

If you don't know what the hydrogen line is, we'll explain it here. Hydrogen atoms randomly emit photons at a wavelength of 21cm (1420.4058 MHz). Normally a single hydrogen atom will only very rarely emit a photon, but the galaxy and even empty space is filled with many hydrogen atoms, so the average effect is an observable RF power spike at ~1420.4058 MHz. By pointing a radio telescope at the night sky and averaging the RF power over time, a power spike indicating the hydrogen line can be observed in a frequency spectrum plot. This can be used for some interesting experiments, for example you could measure the size and shape of our galaxy. Thicker areas of the galaxy will have more hydrogen and thus a larger spike, whereas the spike will be significantly smaller when pointing at empty space. You can also measure the rotational speed of our galaxy by noting the frequency doppler shift.

The 2.4 GHz parabolic WiFi grid dishes can be found for a cheap at US$49.99 on eBay and for around US$75 on Amazon. Outside of the USA they are typically carried by local wireless communications stores or the local eBay/Amazon equivalent. If you're buying one, be sure to get the 2.4 GHz version and NOT the 5 GHz version. If you can find 1.9 GHz parabolic grid dish, then this is also a good choice. Although we haven't tested it, this larger 2.4 GHz grid dish would probably also work and give slightly better results. WiFi grid antennas have been commonly used for GOES and GK-2A geosynchronous weather satellite reception at 2.4 GHz with RTL-SDRs as well and we have a tutorial on that available on our previous post.

These dishes are linearly polarized but that is okay as hydrogen line emissions are randomly polarized. Ideally we would have a dual polarization (NOT circular polarized) feed, but linear appears to be enough and is much simpler. In addition, the 2.4 GHz feed is obviously not designed for 1420 MHz, but just like with GOES at 1.7 GHz the SWR is low enough that it still works.

The Gyfcat animation below shows a hydrogen line "drift" scan performed with the 2.4 GHz WiFi dish, an RTL-SDR Blog V3 and a NooElec SAWBird H1 LNA. The scan is performed over one day, and we simply let the rotation of the earth allow the Milky Way to drift over the antenna. The Stellarium software on the left shows the movement of the Milky Way/galactic plane over the course of a day for our location. The dish antenna points straight up into the sky, and we have set Stellarium to look straight up too, so Stellarium sees exactly what our dish antenna is seeing.

You can clearly see that there is a lump in the radio spectrum at around 1420.40 MHz that grows when parts of the Milky Way pass over the antenna. This lump is the hydrogen line being detected. As our Milky Way galaxy is filled with significantly more hydrogen than empty space, we see a larger lump when the antenna points at the Milky Way, and only a very small lump when it points away.

It's important to ignore the very narrowband spikes in the spectrum. These narrowband spikes are simply radio interference from electronics from neighbors - probably TVs or monitors as we note that most of the interference occurs during the day. There is also a large constant spike which appears to be an artifact of the LNA. The LNA we used has a 1420 MHz filter built in, but LCD TVs and other electronics in today's suburban environment spew noise all across the spectrum, even at 1420 MHz.

You can also note that the hydrogen line peak is moving around in frequency as different parts of the galaxy pass overhead. This indicates the doppler shift of the part of the galaxy being observed. Because the arms of the galaxy and the hydrogen in it is rotating at significant speeds, the frequency is doppler shifted relative to us.

Using the power and doppler shift data of the hydrogen line is how astronomers first determined the properties of our galaxy like shape, size and rotational speed. If we continued to scan the sky over a few months, we could eventually build up a full map of our galaxy, like what CCERA have done as explained in this previous post.

Hardware Required

1. A 2.4 GHz WiFi parabolic grid dish. (~$50)

2. A low noise amplifier (LNA). This is required to get the noise figure of the receiving system low enough, and the gain high enough.

1. We recommend using a hydrogen line specific LNA. Good models include the NooElec SAWBird+ H1 ($44.95), or the GPIO labs Hydrogen Line pre-filtered LNA ($49.95).

Using a specially made hydrogen line LNA with filtering built in will get you better results compared to a general purpose wideband LNA. It may also be mandatory to use one of these LNAs for those living in areas with strong interfering signals from things like cellular and broadcast FM/TV etc.

2. If you're on a budget, and don't have many strong interfering signals around you, then you get away with using an unfiltered general purpose wideband LNA like an LNA4ALL or our $19 RTL-SDR Blog wideband LNA.

We can generally get away with an unfiltered LNA if we point the antenna straight up towards the sky, or at a high elevation. This avoids most terrestrial sources of noise from leaking into the antenna. However, the H-Line specific LNAs are usually very high gain, and very low noise figure, so can work better for this type of experiment.

3. An RTL-SDR Blog V3, or any other RTL-SDR with a built in bias tee (~$21.95). An Airspy is also a good choice with good supporting software, but costs a lot more.

4. A Type N Male to SMA Male adapter (~$7 on Amazon, cheaper elsewhere). Most WiFi grid antennas have an N-female connector so we need to convert to SMA to connect to the RTL-SDR.

5. A high quality USB extension cable (~$10), just long enough to get to your PC/laptop. We recommend a high quality USB3.0 spec cable, as these have much lower voltage loss over longer runs. If you're using an active cable, make sure it can handle the voltage drop.

6. Some sort of tripod ($39.99) to mount your dish, or another way to mount it. You could probably even just lay it on the ground.

7. A 50 Ohm terminator ($5.50) (optional but recommended)

8. A Windows PC or Laptop (for this tutorial). A Raspberry Pi could also work with other software or as a TCP server.

Total cost (not including the PC): US$179.40, and probably less if you already have some parts or find similar items priced cheaper elsewhere.

Hardware Setup

The recommended setup is simple. Antenna pointed straight up -> LNA -> RTL-SDR -> USB Cable -> PC.

Detailed instructions below:

1. Construct the WiFi dish. This is just a matter of putting in a few screws to join the two panels and feed. Make sure the feed is mounted with the long axis matched with the grid direction. Also ensure the reflector is installed.

2. Mount the dish outside pointing straight up into the sky. Once you are a little more advanced, you could try other elevations or even motorize it, but start with straight up for now. The rotation of the dish does not really matter as hydrogen line emissions are randomly polarized.

3. Connect the RF side of the LNA to the antenna cable via the N-SMA adapter.

4. Connect the RTL-SDR to the RF+DC side of the LNA.

5. Connect a high quality USB cable from the RTL-SDR to your PC. We don't recommend using anything more than a few meters of coax between the LNA and RTL-SDR in order to optimize the signal levels.
Do not use coax between the antenna and LNA. The LNA should be directly connected to the antenna output.

It may also be wise to waterproof your LNA and RTL-SDR if kept outdoors. This can be as simple as putting it in a plastic bag, or old coke bottle sealed with some putty.

Software Setup

In order to detect the hydrogen line we need to use software capable of integrating/averaging many FFT samples over time. Averaging the samples reduces the SDRs quantization noise, allowing the weak hydrogen line peak to be seen. Because the galaxy is moving fairly slowly in the sky, we can safely average for 5-10 minutes at a time.

For Linux, there are various programs that can be used. PICTOR, and rtl-obs are some good choices, but are a little more complicated to set up. But they have some good features like the ability to properly calibrate the results, and some interesting algorithms that could increase the SNR of the hydrogen line detection.

For this tutorial we will keep it as simple as possible, and we will use Windows, with SDR# and a SDR# plugin called "IF Average". We will also use a free astronomy program called Stellarium for tracking the Milky Way's galactic plane across the sky.

Stellarium Setup

1. Download Stellarium from https://stellarium.org, and download the Windows version using the button up the top.

2. If you opened Stellarium during the day you won't see any stars due to atmosphere simulation. Hit the 'a' key on the keyboard to disable atmosphere.

3. Hit the F4 key to go into the options menu. Here we recommend increasing the brightness of the Milky Way to 6.0, to make it really obvious.

4. We also suggest going to the markings tab, and turning ON the Azimuthal grid, which will provide a marker to Zenith (straight up in the sky).

5. Check the location shown in the bottom left. If it's not right for you, press F6 to set the correct location.

6. Use the mouse wheel or pinch controls to zoom out so that the entire sky is visible. Drag the mouse so that the camera is looking at Zenith (straight up into the sky).

7. As Stellarium will have opened by default in full screen mode, press F11 to go to Windowed mode.

By clicking on an object within the Milky Way or behind it, you can find out the Galactic coordinates of where in the Galaxy you are pointing. This could be useful for comparing with already known results like those shown here. Right click to remove the info text about that object.

SDRSharp with IF Average Plugin Setup

Install SDRSharp, Blog V3 drivers, and the IF Average Plugin

1. Download the latest version of SDR# from www.airspy.com. Set up SDR# and the RTL-SDR as described in the Quickstart Guide at www.rtl-sdr.com/QSG.

2. For easily activating the bias tee on the RTL-SDR Blog V3, download the special Blog V3 Windows drivers from https://github.com/rtlsdrblog/rtl-sdr-blog/releases.

3. Rename the original rtlsdr.dll file in the SDR# folder to rtlsdr_old.dll.

4. Copy over all the .dll files in the Release.zip file.

5. Rename librtlsdr.dll to rtlsdr.dll.

6. Download the IF average plugin. Unfortunately the author of the plugin has not maintained his website, and the page is now offline. But the plugin is still available on his Dropbox. Go to Download->Direct Download to download it to your PC. We have also decided to mirror the plugin here on the blog server just in case the Dropbox file goes offline.

7. Extract the plugin files from the zip file into the SDR# folder.

8. Open the "Magic sentance.txt" file and copy the <add key...> line.

9. Open plugins.xml with notepad, and copy and paste in the <add key...> line.

Receiving and Averaging the Hydrogen Line FFT

1. Open SDR#, select the RTL-SDR, press the start button.

2. Adjust the RF Gain slider to the maximum, and check the "Offset Tuning" checkbox to enable the bias tee via the V3 driver hack.

3. Tune to 1420 MHz and use the center tuning button to center the frequency (the button next to the frequency input in SDR#).

4. Now on the left scroll down until you find the IF Average plugin that you installed earlier. (NOTE: On newer versions of SDR# the plugin is hidden by default! To unhide it, click on the top left 'hamburger' icon (the three horizontal lines to the left of the play/stop button). Then click on the 'IF Average' entry to enable it)

5. We used the following settings which results in a 6-7 minute averaging time (but shorter averaging times would probably also work - try reducing the dynamic averaging a little):

1. FFT resolution: 1024

2. Intermediate Average: 1000

3. Gain: ~335

4. Level: 1000

5. Dynamic Averaging: 902000

6. Calibration: Connect your LNA to the 50 Ohm terminator for initial calibration. If you don't have a 50 Ohm terminator, just leave the antenna disconnected.

7. Check the "Window" checkbox, and immediately press the "Background" button in order to generate a reference background scan. This scan will be subtracted from subsequent scans thus removing the unwanted curved shape of the RTL-SDR and LNA filters. The first scan will take 6-7 minutes.

8. Once the background scan is completed, you'll see the words "Corrected background!" in yellow in the top left of the FFT average window.

9. You can now reconnect the antenna.

Tip: If the FFT Average Window keeps disappearing behind the main SDR# window, push the main SDR# window to the right and bring the IF Average Window to the left so that it does not sit on top of SDR#.

10. You may need to adjust the Gain and Level sliders a little bit in order to get the FFT graph on the screen. Try to keep the Gain large, as this increases the FFT gain allowing you to see small peaks more clearly.

At this stage you now just need to wait for the Milky Way to enter your antennas beamwidth, and watch for the H-line peak. The software will continually average the spectrum.

If you want to create a timelapse like the gif shown at the top of the post we can recommend a program called " Chronolapse", which takes a screenshot every X minutes. You can then convert those images into a movie or gif. The IF average plugin can also output data files which could be used for further analysis.

If you do not do the calibration at all, your spectrum will appear quite wavy. Be sure to not confuse those waves with the hydrogen line peak.

Example Results

Other Notes

It is possible to get slightly higher SNR by covering the grid dish with foil, or a metal mesh. However, the improvement appears to be very small, almost negligible since the WiFi feed is only linearly polarized.

Longer integration/average times will spread the peak out more. Smaller integration times may result in less SNR.

You may wish to experiment with an elevation that maximizes the time spent pointing at the Milky Way for your location. Use Stellarium and the time shift feature (F5, or CTRL+ClickDrag) to find the optimal elevation. But lower elevations are more susceptible to man made interference.

A motorized antenna mount would allow you to scan more of the Milky Way in one day. An example build from this previous post here.

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Cheap and Easy Hydrogen Line Radio Astronomy with an RTL-SDR, WiFi Parabolic Grid Dish, LNA and SDRSharp

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We've recently been testing methods to help budding amateur radio astronomers get into the hobby cheaply and easily. We have found that a low cost 2.4 GHz 100 cm x 60 cm parabolic WiFi grid antenna, combined with an RTL-SDR and LNA is sufficient to detect the hydrogen line peak and doppler shifts of the galactic plane.

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PARAMETERS Horn type: Pyramidal Conical E-plane sectoral H-plane sectoral Corrugated pyramidal Corrugated conical Diagonal Dual-mode ...

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Calculations for the waveguide and antenna length 

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Calculations for the waveguide and antenna length 

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Abstract : Van de Hulst predicted the existence of the radio emission of neutral hydrogen at 21 cm and in 1951 Ewen and Purcell succeeded in detecting this emission with the horn antenna shown above. In this post we want to describe the design and the construction of a low cost horn antenna with the aim to detect and measure this emission coming from our milky way.
Introduction

The hydrogen 21-centimeter line is the electromagnetic radiation spectral line that is created by a change in the energy state of neutral hydrogen atoms. This electromagnetic radiation is at the precise frequency of 1420.4 Hz, which is equivalent to the vacuum wavelength of 21.1 cm in free space. This wavelength falls within the microwave region of the electromagnetic spectrum, and it is observed frequently in radio astronomy, since those radio waves can penetrate the large clouds of interstellar cosmic dust that are opaque to visible light. The study of this radio emission can help us to evaluate the presence of hydrogen in interstellar clouds and to understand the structure of our milky way.

Design

Neutral hydrogen radiates at 1420.4 MHz, and studies have shown that red and blue shifts of up to 2 MHz may be observed. Therefore our goal is to design a horn antenna to receive signals in the range of 1420.4 ± 2 MHz. The antenna is just a length of copper wire cut to l =5.25 cm, about a quarter of the wavelength λ =21.1 cm corresponding to 1420.4 MHz. With these numbers in mind, we have to design a waveguide and horn to efficiently direct desired frequencies toward the antenna (the copper wire).
An open waveguide is not an effective energy radiator (and similarly an effective receiver) due to the impedance mismatch at the mouth. Things improve by widening the walls of the trumpet-shaped guide, thus coupling the impedance between the waveguide and the intrinsic one of free space.

Waveguide

The first component of the system is the waveguide. As we know waveguide is a hollow metal pipe used to carry radio waves. The electromagnetic waves in a (metal-pipe) waveguide may be imagined as travelling down the guide in a zig-zag path, being repeatedly reflected between opposite walls of the guide. For the particular case of rectangular waveguide, it is possible to base an exact analysis on this view and derive the propagation modes and cutoff frequency.
The drawings below shows a rectangular waveguide with the electrical and magnetic field of the main propagation mode (). The direction of the antenna determines the polarization direction of the wave that is picked up, the electrical field is polarized vertically, parallel to the antenna, the intensity is zero on the surface of the metal waveguide and the maximum intensity is reached inside the waveguide in a position depending on the wavelength of the radiation. The pattern of the propagation mode is also characterized by a waveguide wavelength λG .

The cutoff wavelength - the maximum wavelength that can propagate in the waveguide in the direction of the side "a" - is λ = 2a. This is equivalent to saying the waveguide acts as a high pass filter with cutoff frequency of ν = c/λ. The following drawing can help to understand this behavior of the waveguide. In order to minimize dispersion in velocity down the waveguide in the range of interest, a waveguide should be used for frequencies greater than 1.25*ν . Additionally, in order to suppress higher order modes they should be used for frequencies less than 1.9*ν.

Now we have all the data to design our waveguide. Fortunately we can use for this purpose a normal 5lt can (for example a can for oil). The measures of this rectangular container are the following : a = 146 mm, b = 117 mm. We check, referring to the following drawing, that all conditions are verified and we proceed to the calculations for positioning the antenna.

Neutral Hydrogen Emission FrequencyRadio Emission Data
f = 1420,4 MHz -
Δf = 2 MHz
f = 1420,4 ± 2 MHz
λ = 21,1 cm - Wavelength
l = λ/4 = 5,25 cm - Quarter Wave Antenna

Horn

A horn antenna or microwave horn is an antenna that consists of a flaring metal waveguide shaped like a horn to direct radio waves in a beam. Horns are widely used as antennas at UHF and microwave frequencies, above 300 MHz. An advantage of horn antennas is that since they have no resonant elements, they can operate over a wide range of frequencies, a wide bandwidth. Our antenna is a " Pyramidal horn" : a horn antenna with the horn in the shape of a four-sided pyramid, with a rectangular cross section.
By adopting the measures of similar projects, where a compromise was made between gain and size, we chose the following measures. In addition, our horn antenna will have to connect with the rectangular waveguide described above.

With an online application we have determined the antenna gain that turns out to be Gain = 18.16 dB ≈ 18 dB

The beam width can be calculated from the geometry of the antenna. We limit ourselves to reporting the values ​​we obtained from antennas built with similar geometries.

● Gain : 18 dB
● Half Power Beam Width : 20° H-plane, 24° E-plane

These data are however in accordance with the general theory that assigns an angular resolution to an antenna given by the relation:
Δθ ≅ λ/D = 21/75 = 0.28 rad = 16°
The horn antenna is a rather directive antenna, however the dimensions of our antenna are limited and this makes the angle covered rather large. The spatial resolution of our antenna will therefore be about 16° and will not allow us to resolve structures with a spacing of less than 16°. The extension of the radio sources obtained with the antenna will be the convolution of the real extension with the radiation pattern of the antenna : in practice this means an enlargement of the detected dimensions. We report below as an example the radiation pattern of a similar pyramidal horn antenna.

Building

For the construction of our antenna we used a 5lt can as a basis for the waveguide and then we had the 1.2 mm thick raw aluminum sheet cut and bent by a workshop for the construction of the horn.

Waveguide

The upper part was cut from the can, then we cut the edges to leave an integral part of the calculated length of 23 cm. We left the side flaps that will be used for fixing on the aluminum sheet. In the calculated position, a hole was made for a type N panel connector, on which a piece of a thin brass tube was welded which constitutes the actual antenna. An N-SMA adapter is connected to the panel connector, fixed with four screws. The images below show the waveguide.

Horn

The horn was assembled from sheet metal cut and folded according to the following drawing.

The waveguide was then fixed to the horn using the edges of the can itself fixed with screws and aluminum adhesive tape. The aluminum adhesive tape was also used to cover the joints between the sheets and with the can so that the inside of the horn is as flat and homogeneous as possible. To increase the rigidity of the structure it may be useful to glue aluminum profiles, for example square shaped, on the four major sides of the horn: in this way the sheets are prevented from deforming due to their own weight.

Antenna Stand

For the mechanical support of our horn antenna, we used a simple wooden bench on which we hinged a wooden base on which the waveguide and the pyramidal horn rest. The inclination is adjusted simply, by raising or lowering the antenna and inserting an adequate support under the base.

References

The Intenet contains numerous examples of antennas and receivers for the emission of neutral hydrogen at 21 cm. At the following link there is the description of an excellent similar project : A site very rich in information (I would say indispensable ..) is the following probe-the-galaxy-on-a-shoestring-with-this-diy-hydrogen-line-telescope, and this is the related documentation : Hydrogen Line Project Documentation.
DSPIRA

Next Step

This project continues with the construction of the receiver : Low-Noise SDR-Based Receiver for the 21cm Neutral-Hydrogen Line

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Donation

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Horn Antenna for the 21cm Neutral-Hydrogen Line - PhysicsOpenLab

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Abstract : Van de Hulst predicted the existence of the radio emission of neutral hydrogen at 21 cm and in 1951 Ewen and Purcell succeeded in detecting this emission with the horn antenna shown above.

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Inspiration for the horn antenna project started here

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Inspiration for the horn antenna project started here

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Video Example of data collected to see the 21 cm hydrogen line and the rotation of the Milky Way

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Video Example of data collected to see the 21 cm hydrogen line and the rotation of the Milky Way

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My first successful attempt to detect galactic hydrogen (Hydrogen line)

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Abstract : In this post we want to continue the study of the structure of our galaxy made using the emission at 21 cm of neutral hydrogen and described in the previous post : Milky Way Structure detected with the 21 cm Neutral-Hydrogen Emission. In particular, we want to exploit the Doppler effect to measure the rotation speed of neutral hydrogen clouds, as a function of the distance from the center, and derive the rotation curve of the galaxy.
Introduction

Neutral hydrogen gas in the disk of our Galaxy moves in nearly circular orbits around the Galactic center. Radial velocities measured from the Doppler shifts of encode information about the distances of Hi clouds from the galactic core. HI is transparent to microwave radiation except in a few regions near the Galactic plane, so the distribution of hydrogen maps out the large-scale structure of the whole Galaxy, most of which is hidden by dust at visible wavelengths.
The image below shows the diagram of our galaxy with the position of the sun. The sun is located in a secondary arm, called the Orion arm, between the arms of Perseus and Sagittarius. Rotation occurs clockwise.

Doppler Shift

The Doppler effect (or the Doppler shift) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. We are familiar with the changing pitch of a moving vehicle. For light, this change is given by : where c is the speed of light, v the relative velocity, λe the emitted wavelength, and λo the observed wavelength. Using the relationship λ=cf, we can write the relation in terms of frequency and calculate the relative velocity : We know the emitted frequency because it is measured in laboratory fe=1420.40575 MHz, we know the speed of light and we measure with the radio telescope the observed frequency, so we can calculate the relative speed between the observer (the radio telescope) and the hydrogen cloud.

Tangent Point Method

The value we are interested in, i.e. the tangent speed of the cloud with respect to the galactic center The measurements are made by pointing the radiotelescope towards the first quadrant of the galaxy, with increasing galactic longitude, starting from values ​​close to 0° (direction towards the galactic center) to arrive at values ​​close to 90° (direction parallel to the direction of rotation).
We refer to the diagram on the side where the position of the radio telescope (coinciding with the sun) and the direction of observation are shown, the vector of the speed of the sun is highlighted in yellow and the vector of the speed of the hydrogen cloud in blue. As can be seen from the drawing, the highest recession velocity measured in that specific direction is the one that corresponds to the clouds that orbit tangent to the direction of observation, of course there may also be other contributions from closer or more distant clouds but, with respect to the point of observation (the sun) they will have ever lower recession.
By measuring the frequency spectrum and calculating the relative speed with the Doppler effect formula, we obtain the velocity distribution of the hydrogen clouds and, among these, we must take the highest value corresponding to one of the relative maxima. This measurement procedure must be repeated, as we said above, for increasing galactic longitudes, in order to obtain a mapping of the entire first quadrant.
Vtp/gc, must however be calculated by adding the value obtained from the measurement, which is the value of the tangent speed of the cloud with respect to the sun, Vtp/s, with the value of the rotation speed of the sun along the direction of observation, Vs/gc.

With a bit of trigonometry we can write :
Vtp/gc = Vtp/s + Vs/gc = Vobs + Vsun*cos(90 - Θ) = Vobs + Vsun*sin(Θ) d = Ro*sin(Θ)
Where :
Vsun = 220 Km/s
Ro = 7.6 Kpc
Vobs = speed calculated from measurements with the radio telescope

Correction for Local Movements

Of course things are not so simple ... The speed value we obtain by applying the Doppler effect formula, must be corrected by removing the contribution of three movements that affect the movement of the observer (our radio telescope), compared to the "simple" rotation around the galactic center :
- the rotational motion of the earth
- the revolution motion of the earth around the sun
- the motion of the sun within the local group of stars

When we took into account these three movements we placed ourselves in what is called: local reference system (local standard rest). To obtain the value to remove (or add) you can refer to the following link : https://www.gb.nrao.edu/cgi-bin/radvelcalc.py

Measures

Those shown below are the graphs of the speeds we obtained with our radio telescope. The values ​​always refer to the "standard local rest". For each measurement we report galactic longitude and latitude. Latitude is always close to 0 °. The velocity distribution was approximated by four Gaussian curves, for which we report the average velocity value corresponding to the maximum of the curve. In our simplified hypothesis, the Gaussian curves should correspond to as many hydrogen clouds moving with respect to the observer.

The first curve that we report differs from the following ones because it corresponds to the observation made at a longitude of about 180 °, that is towards the outside of the galaxy in the opposite direction to that towards the center. If our rotational hypotheses are correct, the measured relative speed should be practically zero since the radial component of speed is zero. The measurement agrees excellently with the predictions since we got just a zero speed value, as can be seen in the graph below.

Subsequent measurements refer to increasing values ​​of galactic longitude, starting from an initial value of 12°. As can be seen from the graphs, the main peak, which should correspond to the local clouds present in the Orion arm, remains at speeds always close to zero, this is consistent with the fact that they are local clouds rotating at the same speed as the sun. As longitude increases, the contribution of components with greater redshift increases, until it reaches a maximum at about 45 °, and then decreases as longitude increases further. These higher redshifts should correspond to emissions from clouds in innermost locations that are away from the sun.

Galaxy Rotation Curve

With the data collected in the observations we have prepared the table below in which we insert the galactic longitude, the measured speed value, the value of the sun's speed along the measurement direction, the speed Vtp resulting from the sum of the two components and the distance corresponding to longitude, calculated with the trigonometric formula.

The data in the table are shown in the following graph which represents the trend of the rotation speed of the galaxy as a function of the distance from the center. Our measurements have a great uncertainty due above all to the imprecision of the radiotelescope pointing system and to the poor angular resolution, moreover the frequency resolution, although good, does not always allow a clear separation of the different components that make up the spectrum.
Despite these limitations, the result is appreciable because it clearly shows an initial increasing section, followed by a plateau with values ​​that average around 225 Km/s. This trend is very similar to the rotation curves found in the scientific literature, we report an example in the next graph.

The rotation models of the galaxy, based on the estimate of the mass distribution, predict that the rotation speed decreases as the distance from the center increases. The estimate is based on observations showing that most of the galaxy's mass is concentrated in the interior. In this configuration a "Keplerian" model is applied (a bit like the solar system which has its mass concentrated in the sun) which predicts that the rotation speed is proportional to The data, on the other hand, say that the speed remains more or less constant even as the distance from the center increases.This anomalous behavior, common to most galaxies, is an indication of the existence of the mysterious 1/√r, that is, it decreases as the distance increases.
dark matter, which would be distributed in a large halo around the galaxy. Dark matter would be the missing mass needed to explain the "anomalous" rotation curves of most galaxies.

Conclusions

The self-built 21cm radio telescope has allowed us to obtain important scientific evidence on the structure and rotation of the galaxy. The limited angular resolution is not a big problem because the hydrogen clouds are distributed objects, while the good frequency resolution has allowed us to study in detail the relative movements and rotation of the hydrogen clouds. All this was possible thanks to the availability of cheap LNAs and filters and the use of the SDR technique for data acquisition and post-processing. The GNURadio open software also made it possible to use and write DSP data processing programs.

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Donation

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Measurement of the Milky Way Rotation - PhysicsOpenLab

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Abstract : In this post we want to continue the study of the structure of our galaxy made using the emission at 21 cm of neutral hydrogen and described in the previous post : Milky Way Structure detected with the 21 cm Neutral-Hydrogen Emission.

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NASA.gov brings you the latest images, videos and news from America's space agency. Get the latest updates on NASA missions, watch NASA TV live, and learn about our quest to reveal the unknown and benefit all humankind.

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2 minutes | 11 Apr 2018

Remote keyless car central locking systems come as standard or as an option in 70% of cars made today. They consist of a key fob transmitter and a receiver inside the vehicle. To work, they need a frequency, which is 433.92MHz in Europe (315MHz the U.S. and Japan). To meet the demand for remote keyless entry systems, Europe has also opened up the 868MHz band.

How does a keyless entry system work?

Let's break it down, what is keyless entry, :

1. When you press a button on your key fob, you're waking up its Central Processing Unit (CPU) inside.

2. The CPU sends a data stream to the radio frequency (RF) transmitter. The keyless remote is actually a radio.

3. This data stream contains command and for security, rolling codes.

4. The remote keyless system's receiver in the car captures the RF signal, extracts it and sends the data stream to the CPU.

5. The CPU decodes it and sends commands to the command module.

Design challenge

Manufacturers have to consider how to produce a robust and reliable system with low-current consumption that can achieve a good range, at as low a cost as possible.

Battery life is key, for both the transmitter and receiver, which must always be on, ready to receive a transmission. Some systems are designed to leave the receiver on for a short amount of time. It goes into sleep mode for the rest of the time, but can 'wake up' fast when needed.

Passive keyless entry (PKE)

For the ultimate in driver comfort and convenience, you can lock and unlock your car and start the engine - without even holding your key. You simply need to have it on you, whether in your pocket or handbag. These type of systems, sometimes called Smart Keys or Passive Keyless Entry, are common in luxury cars.

When the driver approaches their car, they're identified by a paired radio transponder chip inside the car key. The doors unlock and open by when the driver pulls the handle. The engine starts with the touch of a button on the dashboard. The button is doing the job of the key by closing the circuit on the engine.

This isn't merely for convenience, though. The start/stop button is supposed to provide better protection against from car thieves. The car's computer can only recognise the code from the driver's specific key fob. Without the fob, the car can't be stolen.

Locking the car when exiting is just as simple. The driver merely pushes a button on the door handle - some systems even lock when the driver walks out of range. Some cars even have keyless boot opening systems with sensors on the back bumper. Shake your foot underneath the bumper and the boot opens, which is especially convenient if your hands are full.

Any problems with remote keyless entry systems?

As mentioned earlier, without the fob, the car can't be stolen. That's the theory, anyway. Thieves, however, are rising to the challenge, using radio transmitters to perform 'relay' car hacks to capture the signal from the car's fob. To get around this, car owners can check with their dealers to see if there are any software updates that can be performed. Another trick: if the fob can be turned off overnight, do so.

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Explaining remote keyless entry in cars | Global Manufacturer & Distributor of Component Solutions - Essentra Components

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2 minutes | 11 Apr 2018 Let's break it down, what is keyless entry, : When you press a button on your key fob, you're waking up its Central Processing Unit (CPU) inside. The CPU sends a data stream to the radio frequency (RF) transmitter. The keyless remote is actually a radio.

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Understanding the Milky Way rotation using radio telescope observations

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Understanding the Milky Way rotation using radio telescope observations

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I-LOFAR CPD resources

The I-LOFAR consortium understands the importance of giving teachers support and resources that reflect the changing expectations of STEM education, which aims to give students the knowledge and tools for success. This page contains continuous professional development (CPD) resources developed by the AstroLands team at I-LOFAR. These include resources aimed at Primary School teachers (for 5th and 6th class students, aged 10-12) and Junior Cycle science teachers (for 1st, 2nd and 3rd year students, aged 11-15) and are free to download.

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The I-LOFAR consortium understands the importance of giving teachers support and resources that reflect the changing expectations of STEM education, which aims to give students the knowledge and tools for success. This page contains continuous professional development (CPD) resources developed by the AstroLands team at I-LOFAR.

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NUCLIO - Núcleo Interativo de Astronomia e Inovação em Educação

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Fantastic courses and resources for teachers in astronomy.

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© 2021 National Schools' Observatory. All Rights Reserved.

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National Radio Astronomy Observatory - National Radio Astronomy Observatory

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Welcome to the home of the National Radio Astronomy Observatory online.

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NASA.gov brings you the latest images, videos and news from America’s space agency. Get the latest updates on NASA missions, watch NASA TV live, and learn about our quest to reveal the unknown and benefit all humankind.

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Educator Resources

We have compiled a list of radio astronomy resources for educators to use in the classroom.

Large Group Activities developed by the LoCo Lab

Radio Astronomy Crossword Puzzle
A thought-provoking crossword puzzle filled with radio astronomy words! Click here for the solution.Word Search
A word search using some radio astronomy terms. Click here for the solution.

Giant Wordsearch Puzzle
A huge worsearch puzzle that we developed for our events that is equally well suited to classroom activities. We printed the poster out at its full size of 42″ by 56″, and laminated it with 5mm thick plastic. We use Expo Vis-a-Vis Wet Erase markers to color on the poster. The ones we use can be found on Amazon. Click here to open. Here is the solution.

Giant Color-by-Numbers
A huge color-by-numbers puzzle that we developed for our events that is equally well suited to classroom activities. We printed the poster out at its full size of 42″ by 56″, and laminated it with 5mm thick plastic. We use Expo Vis-a-Vis Wet Erase markers and Sanford Wet Bright Sticks Wet-Erase Fluorescent Markers to color on the poster. The ones we use can be found on Amazon. Click here to open. The solution is attached to the activity. The image is adapted from Hubble's picture of M51 "The Whirlpool Galaxy."

Videos by the LoCo Lab

Classroom Activities

Quiet Skies
NRAO developed the Quiet Skies Project to introduce your middle/high school students to radio astronomy through an inquiry-based project to measure radio frequency interference in your community.

SALSA Telescope Data Collection and Interpretation
Use an actual telescope in Sweden to collect data! Salsa Onsala is a 2.3 m radio telescope operating at a wavelength of 21 cm. At this wavelength, one can observe the spiral arms of the Milky Way (our galaxy). The radio telescope can be operated remotely over the Internet. To detect cosmic signals while watching the telescope move in the webcam is a great thrill for both pupils and teachers. Observations can be done during day-time as well as night-time, and even in bad weather.
Hands-On Radio Astronomy Mapping the Milky Way Directions
United States Frequency Allocation Chart
The August 2011 edition of the United States Frequency Allocations: The Radio Spectrum Chart.

Lesson Plans

Radio Astronomy Teacher's Guide and Activities
Listening to Space: Radio Astronomy was originally designed as preparation for planetarium shows. It has a variety of activities for explaining radio astronomy!

Telescope Arrays

National Radio Astronomy Observatory
Information about various radio telescope arrays and the most recent news updates on their research.

Other Outreach Resources

Multiwavelength Astronomy
The University of Chicago has an impressive website for learning about different wavelengths of light.

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We have compiled a list of radio astronomy resources for educators to use in the classroom. Radio Astronomy Crossword Puzzle A thought-provoking crossword puzzle filled with radio astronomy words! Click here for the solution.Word Search A word search using some radio astronomy terms. Click here for the solution.

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Colour info for list above:

New beacon

Inactive beacon

Beacon info updated

Heard within last 5 days by me

Zusatz-Infos der Liste:

Neue Bake

Ausser Betrieb

Bake mit neuer Info

In letzten 5 Tagen von mir gehört

More beacon info/Zusätzliche Infos zu Baken

Graphics for 10 m beacon audibility in C.Europe/Grafiken zur Baken Hörbarkeit in DL:

last 3 months/letzte 3 Mon. &nbsp &nbsp current year/lfd.Jahr &nbsp &nbsp total chart/alle Jahre
last 8 years compared/letzte 8 Jahre im Vergleich 2004 to 2013 compared/2004 bis 2013 im Vergleich
2003 chart &nbsp &nbsp 2004 chart &nbsp &nbsp 2005 chart &nbsp &nbsp 2006 chart
&nbsp &nbsp 2007 chart &nbsp &nbsp 2008 chart &nbsp &nbsp 2009 chart &nbsp &nbsp 2010 chart &nbsp &nbsp 2011 chart &nbsp &nbsp 2012 chart &nbsp &nbsp 2013 chart &nbsp &nbsp 2014 chart &nbsp &nbsp 2015 chart &nbsp &nbsp 2016 chart &nbsp &nbsp 2017 chart &nbsp &nbsp 2018 chart &nbsp &nbsp 2019 chart &nbsp &nbsp 2020 chart Please note that e-mail addresses show <at> instead of @
Hinweis: Bei den E-mail Adressen muss jeweils <at> durch @ ersetzt werden

Please send info/update/comments to mail<at>dl8wx.de

Back to top/Zum Listenanfang Zurück zur deut. Startseite Back to Engl. homepage

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amateurfunkbaken bakenliste dl8wx kurzwelle beacons beaconlist shortwave

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Worldwide list of active amateur radio beacons on shortwave. Weltweite Liste zu aktuellen Amateurfunkbaken auf Kurzwelle

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Good website for RTL-SDR projects

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Over on our store we've recently released our new receive only dipole antenna kit which now replaces the older magnetic whip style antennas from the previous kit. This was done for a few reasons including 1) We believe that the dipole kit is much more versatile and will enable beginners to get better reception straight away, 2) magnets of any type are no longer welcome on most airmail parcel carriers (though they still get through for now). While the magnetic whip still works perfectly fine, the dipole kit should make it easier to get the antenna outside or in a better position away from noisy computers/electronics, and it also allows for a simple v-dipole configuration for satellite reception.

The units are currently in stock at our Chinese warehouse either bundled with an RTL-SDR or as an individual antenna set.

This post is a guide on how to use the dipole antenna set in various configurations. First we'll show and explain about what's included in the set:

1x dipole antenna base with 60cm RG174 cable and SMA Male connector. This is the dipole base where the telescopic antennas connect to. The short run of RG174 is decoupled from the base elements with a ferrite choke. This helps to prevent the feed line from interfering with the dipole radiation pattern. On the inside of the base the two dipole element sides are connected with a 100 kOhm resistor to help bleed off any static. The dipole has a 1/4 inch female screw on the bottom, which allows you to use standard camera mount products for mounting.

1x 3 meter RG174 coax cable extension. This coax cable extension allows you to mount the antennas in a place that gets better reception. E.g. outside on a window, or higher up.

2x 23cm to 1 m telescopic antennas. The telescopic dipoles are detachable from the dipole base via a M5 thread which allows for greater portability and the ability to swap them out. These long telescopic antennas cover VHF to UHF.

2x 5cm to 13cm telescopic antennas. These smaller antennas cover UHF to 1090 MHz ADS-B, and even still work decently up to L-band 1.5 GHz frequencies.

1x flexible tripod mount with 1/4" male screw. This piece allows you to mount the dipole on a variety of different locations. E.g. a pole, tree branch, desk, door, window sill. The legs of the tripod are bendy and rubberized so can wrap securely around many objects.

1x suction cup mount with 1/4" male screw. With this mount you can mount the dipole on the outside of a window, on a wall, car roof/window, or on any other smooth surface. To use first clean the surface with window cleaner or isopropyl alcohol. Then place the suction cup on the cleaned surface and close the lever to activate the suction.

Dipole Orientation

Signals are normally transmitted with either horizontal, vertical or right hand/left hand circular polarization (RHCP/LHCP). This is essentially the 'orientation' of a signal, and an antenna with the same polarization should be used too for best performance. A dipole can be used in either vertical or horizontal polarization, just by orienting it either vertically or horizontally.

If you mismatch vertical and horizontal polarization or RHCP and LHCP you'll get an instant 20dB loss. If you mismatch vertical/RHCP, vertical/LHCP, horizontal/RHCP, horizontal/LHCP you'll only get a 3dB loss.

For vertical polarization you will want to have the element connected to the center coax conductor pointing UP. You can confirm which element is connected to the center conductor by temporarily removing the black lid on the dipole base (it can be easily pried off with a nail or flat head screwdriver).

There are also ways to optimize the radiation pattern with dipoles. For example for LEO VHF satellites you can use a V-dipole configuration. You can also make a somewhat directional antenna by using a bent dipole configuration. Some more examples of dipole configurations can be found on KK4OBI's page on bent dipoles.

Terrestrial Signal Reception

Most signals broadcast terrestrially (on Earth) are vertically polarized.

To use the dipole for vertically polarized signals, all that you need to do is orient the elements vertically (up and down).

When used in the vertical orientation, the element connected to the center conductor should be pointing UP. You can check which element is connected to the center conductor by removing the top cap on the dipole base. This will let you look inside at the connections.

Satellite Reception

The dipole can be used in a V-Dipole configuration for polar orbiting satellite reception. See Adam 9A4QV's post where he wrote about how he discovered that it was possible to use dipoles in this configuration for excellent satellite reception. The idea is to use the dipole in horizontal polarization. This gives 3dB loss on the RHCP satellite signals, but also nicely gives 20dB loss on terrestrial signals which could be overloading your RTL-SDR.

For 137 MHz satellites like NOAA and Meteor M2 extend the larger antenna elements out to about 53.4 cm each (about 2.5 sections). Angle the dipole so it is horizontal and in a 'Vee' shape, at about 120 degrees. Place the dipole in the North-Source direction.

With an appropriate L-band LNA like the Outernet LNA the dipole can also somewhat work to receive L-band satellites. Using the smallest antenna collapsed, use a V-dipole configuration and point it towards the L-band satellite. Ideally use a reflector too. In the image below we used a simple cookie tin as a reflector. A hole was drilled into the center and the mount used to clamp in the antenna. This together with the Outernet LNA was enough to receive AERO and STD-C.

Choosing the Antenna Element Length

Like with the whip you can use an online calculator to calculate the optimal length for your frequency of interest. We recommend this dipole calculator. The exact length does not matter too much, but try to get the lengths as close to what the calculator says as you can. With the dipole you want both elements to be the same length.

In reality extending the antenna to almost any random length will work just fine for most strong signals. But if you're really trying to optimize those weak signals you'll want to fine tune the lengths.

Basically the longer the antenna, the lower it's resonant frequency. The shorter the antenna, the higher the resonant frequency. You want to be close to the resonant frequency. Remember that there is about 2cm of metal inside the antenna itself which needs to be added on. Below is a cheat sheet for various lengths and frequencies. Note that the length refers to the length of one side of the dipole only (e.g. the length that you need to extend each element out to).

Large Antenna, 5 Sections, 100cm + 2cm is resonant @ ~70 MHz

Large Antenna, 4 Sections, 80cm + 2cm is resonant @ ~87MHz

Large Antenna, 3 Sections, 60cm + 2cm is resonant @ ~115 MHz

Large Antenna, 2 Sections, 42cm + 2cm is resonant @ ~162 MHz

Large Antenna, 1 Section, 23cm + 2cm is resonant @ ~ 285 MHz

Small Antenna, 4 Sections, 14cm + 2cm is resonant @ ~445 MHz

Small Antenna, 3 Sections, 11cm + 2cm is resonant @ ~550 MHz

Small Antenna, 2 Sections, 8cm + 2cm is resonant @ ~720MHz

Small Antenna, 1 Section, 5cm + 2cm is resonant @ ~1030 MHz.

See the SWR plots at the end for a more accurate reading of the resonance points. But in most cases no matter what you extend the length to the SWR should be below 5 at most frequencies which results in 2.5 dB loss or less. More accurate info on VSWR loss graphs can be found in this document from the ARRL "Understanding SWR by Example" (pdf).

Using the Mounts

The suction cup mount allows you to easily place the antenna on a window, or any smooth surface. To use it first clean the surface thoroughly with isopropyl alcohol or glass cleaner. Then apply the suction cup and close the lever to lock it in place. The lever requires some force to push down, and this ensures a strong grip. You can then angle the antenna in the orientation that you need using the ball socket. Once in place close the ring to lock the ball socket in place.

The flexible tripod mount is useful to mounting the dipole to almost everything else. Including tables, doors, poles, trees etc. The legs of the tripod have a flexible metal wire inside and rubber sheath so they can be bent into a position to grip almost anything.

Note that the mounts and RG174 extension allow you to more easily use the dipole antennas outside or in a better indoors position (e.g. on a Window). But please note that like our older magnetic whip we do not recommend permanently mounting this antenna outdoors. This antenna is designed to be a portable antenna that you put up and take down at the end of the day - not for permanent outdoor mounting. It is not protected against water, not grounded so cannot handle a lightning strike and could be damaged with dirt and grime build up. For permanent outdoor mounting you could conceivably fill the inside and hinges of the dipole with silicon putty or maybe even hot glue and ground the antenna yourself, but we have not tested this. The stainless steel antennas won't rust, but dirt and grime could gum up the collapsing mechanism.

Tightening the hinge

Once you've got the orientation of the dipoles the way you want, you might want to tighten the hinge so the elements don't move so easily anymore. To do this simply take a small screwdriver and tighten the screw on the hinge.

Sample VSWR Plots

Other Notes

Note that this is NOT an antenna designed for TXing. It is an RX antenna only. So please do not TX with it unless you really know what you are doing as you could damage your TX radio. You'll probably need to remove the 100kOhm static bleed resistor to TX anyway.

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Over on our store we've recently released our new receive only dipole antenna kit which now replaces the older magnetic whip style antennas from the previous kit.

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Further activity on measurement of velocity and distance of different galaxies

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Further activity on measurement of velocity and distance of different galaxies

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This website provides students with data on different galaxies such as NGC 1357 and allows them to calculate the Doppler shift, velocity of the galaxy, distance to the galaxy and the age of the universe.

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THE HUBBLE LAW

Measurements of Velocities and Distances

Step 3: Finding the velocity of each galaxy
The velocity is relatively easy for us to measure using the Doppler effect. An object in motion (in this case, being carried along by the expansion of space itself) will have its radiation (light) shifted in wavelength. For velocities much smaller than the speed of light, we can use the regular Doppler formula:

The quantity on the left side of this equation is usually called the redshift, and is denoted by the letter z.

The formula for redshift should remind you of the process where you calculated your percentage error: [(your value) - (true value)] / (true value). Thus, we can view the redshift (at least for those galaxies with a recessional velocity much less than the speed of light) as a "percentage" wavelength shift. It is a measure of the ratio between the velocity of the galaxy and the speed of light.

For this lab, all wavelengths will be measured in Ångstroms (Å), and we will approximate the speed of light at 300,000 km/sec. Thus, we can determine the velocity of a galaxy from its spectrum: we simply measure the (shifted) wavelength of a known absorption line and solve the equation v = z * c.
For Example: A certain absorption line that is found at 5000Å in the lab (rest wavelength) is found at 5050Å when analyzing the spectrum of a particular galaxy. We first calculatez:

redshift = [(measured wavelength) - (rest wavelength)] / (rest wavelength)

We find thatz = 50/5000 = 0.001 and conclude that this galaxy is moving with a velocity v = 0.001 * c = 3000 km/sec away from us.

Measuring the Spectral Lines

The velocity of the galaxy is determined by measuring the redshift of spectral lines in thespectrum of the galaxy. The full optical (visual wavelengths) spectrum of the galaxy is shown at the top of the web page containing the spectrum of the galaxy being measured (see link below). Below it are enlarged portions of the same spectrum, in the vicinity of some common galaxy spectral features: the hydrogen transitions hydrogen-alpha (656.28 nm, 6562.8 Å), hydrogen-beta (486.13 nm, 4861.3 Å), hydrogen-delta (410.17 nm, 4101.7 Å) as well as the "K and H" lines of ionized calcium (393.37 and 396.85 nm, 3933.7 and 3968.5 Å). The enlarged portions of the same spectrum are"clickable" and will return a wavelength value corresponding to where you "clicked." Take a brief look at the spectrum for NGC1357 and the analysis of the spectrum. You should try to use similar logic when measuring the rest of your selected galaxies.

You are now ready to do your measurements.

1. Make sure you have a copy of the Data Table from the set of student answer sheets. (PDF)

2. Note that for each galaxy there are two lines of data under each "spectral lines" column. The first line contains the measured wavelength. The second line contains the calculated redshift.

3. Start with NGC 1357 to see if you can duplicate or come close to the values discussed under the analysis. Note how the data table has been filled in for NGC 1357, and make sure you understand what data goes where and what calculations are being done.

4. Move on to the next galaxy, NGC 1832. Note that this galaxy, too, has been measured for you. Again, see if your measurements mimic these data.

5. Use the velocities of these two galaxies as part of the 15 velocities needed to calculate the Hubble constant (leaving you only 13 to do!).

6. Now move on to the next galaxy that you have selected. Starting with the calcium lines, measure the wavelength of the same but shifted line by clicking at the middle of the spectral line (i.e. at the "greatest depth" of absorption or "peak" of emission)in the spectrum of the galaxy. Write this wavelength in the box below the appropriate line designation in your data table. (Note: It is due to the peculiarities of each galaxy that some spectral lines are absent, or show up inemission instead of absorption.)

7. Do this for the rest of your selected galaxies, trying to measure the shifts of at least 3 lines in the spectrum. For each of your galaxies, you will measure, calculate redshifts, average redshifts, derive a velocity (remember: v = z * c). These are the"y" values for your graph. Then you will be ready to find the"x" values -- the corresponding distances.

8. For the galaxies not used simply cross out the row next to the galaxy number.

Step 4: Finding the distance to each galaxy
A trickier task is to determine the distances to galaxies. For nearby galaxies, we can use standard candles such as Cepheid variables or Type I supernovae. But, for very distant galaxies, we must rely on more indirect methods. The key assumption for this lab is that galaxies of similar Hubble type are, in fact, of similar actual size, no matter how far away they are. This is known as "the standard ruler" assumption. We must first calibrate the actual size by using a galaxy to which we know the true distance. We are looking for galaxies in the sample that are Sb galaxies, as we would use the nearby Sb galaxy, M31 the Andromeda galaxy, to calibrate the distances. Weknow the distance to the Andromeda galaxy through observations of the Cepheid variables in it. Then, to determine the distance to more distant, similar galaxies, one would only need to measure theirapparent (angular) sizes, and use the following approximation for small angles:

a = s / d
or:
d = s / a

wherea is the measured angular size (in radians),s is the galaxy's true size (diameter), andd is the distance to the galaxy.
Measuring the Galaxies

It is up to you to decide the criteria you will use in measuring these galaxies. It is suggested that you try to measure as far out as you can see any fuzzy disk.

The angular size of the galaxy is measured by using itsimage. Note that the images used in this lab arenegatives, so that bright objects -- such as stars and galaxies -- appear dark. Note also that there may be more than one galaxy in the image; the galaxy of interest is always the one closest to the center.

To measure the size, simply move the mouse and click on opposite ends of the galaxy, along its longest part. (You will need to make a total of two clicks.)
Take a look at this schematic of a galaxy viewed from three different angles. Thought question: We assume that the spirals are all round, and that their different shapes are simply because we are viewing them from different angles. When measuring the angular sizes of the galaxies, why should you measure along the longest axis only?
The angular size of the galaxy (in milliradians; 1 mrad = 0.057 degrees = 206 arcseconds) will be displayed; write this number down on your data table given in the student answer sheets, under "Galaxy Size."

If, at any point, you make an error while you're measuring (e.g. a mis-click), simply click on the "back" button of your web browser and take the measurement again.

Checking Your Data
It would be a good idea to have your instructor look at your data now, before you do a ton of calculations. You wouldn't want to spend hours of your time only to discover that you made mistakes in steps 3 and 4.

Initial Calculations
If you feel confident of your data, then you are ready for the preliminary calculations:

Velocity Determination
Foreach measured line calculate the (redshift z), and enter this value in the box under the measured wavelength. Then take the average redshift of the measured lines for each galaxy, and enter it on the appropriate column. Finally, use this average redshift to calculate the velocity of the galaxy using the modified Doppler-shift formula:

v = c * z

Distance Determination
Determine the distance (in Mpc) to each galaxy using the following, revised version of the small angle formula. Recall, we have had to make an important assumption: all of these galaxies are about the same actual size. Once you have the angular diameter inmrad (and with some adjusting of units), just take theactual size of each galaxy -- 22 kpc -- and divide it by the measured angular diameter. For example, if one of the galaxies had a measured angular diameter of 0.50mrad, 22 / 0.50 = 44 Mpc.

Details for the manipulation of the units to come out with the correct distances

From calibrations, we know that galaxies of the type used in this lab are about 22 kpc (1 kiloparsec = 1000 pc) across. We may then find the distance to the galaxies:

distance (kpc) = size (kpc) / a (rad)

or equivalently, upon multiplying the left side by 1000 and dividing the right side by 0.001 (which is exactly the same thing):

distance (Mpc) = size (kpc) / a (mrad)

Note that we now have the equation in a form where we can simply substitute the size in kpc (22) and divide it by the angle returned by our measurements (already in mrad).

Last updated on:

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The Hubble Law: Measurements of Velocities and Distances

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THE HUBBLE LAW Measurements of Velocities and Distances The velocity is relatively easy for us to measure using the Doppler effect. An object in motion (in this case, being carried along by the expansion of space itself) will have its radiation (light) shifted in wavelength.

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In radio systems, many different antenna types are used with specialized properties for particular applications. Antennas can be classified in various ways. The list below groups together antennas under common operating principles, following the way antennas are classified in many engineering textbooks.

The dipole, monopole, array and large loop antenna types below typically function as resonant antennas; waves of current and voltage bounce back and forth between the ends, creating standing waves along the elements. Aperture antennas can be resonant or not. Traveling wave antennas are nonresonant types, the current and voltage waves travel in one direction along the antenna elements.

An isotropic antenna ( isotropic radiator) is a hypothetical antenna that radiates equal signal power in all directions. It is a mathematical model that is used as the base of comparison to calculate the directionality or gain of real antennas. No real antenna can produce a truly isotropic radiation pattern, but the isotropic radiation pattern serves as a "worst case" reference for comparing the degree to which other antennas, regardless of type, can project radiation in one direction.

Nearly isotropic antennas can be constructed using multiple small elements, and regardless of type, any antenna very much smaller than a wavelength (say, ≲ wave) will be approximately isotropic. The smaller the antenna, the more nearly isotropic it will be. Nearly isotropic antennas are used as reference antennas for testing other antennas and for field strength measurements, and for backup antennas on satellites which work without the satellite being oriented towards a communication station.

An "isotropic antenna" should not be confused with an " omnidirectional antenna"; an isotropic antenna radiates equal power in all three dimensions, while an omnidirectional antenna radiates equal power in all horizontal directions, with the power radiated varying with elevation angle, but decreasing to zero along the antenna's vertical axis.

The dipole is the prototypical antenna on which a large class of antennas are based. A basic dipole antenna consists of two conductors (usually metal rods or wires) arranged symmetrically, with one side of the balanced feedline from the transmitter or receiver attached to each. The most common type, the half-wave dipole, consists of two resonant elements just under a quarter wavelength long. This antenna radiates maximally in directions perpendicular to the antenna's axis, giving it a small directive gain of 2.15 dBi. Although half-wave dipoles are used alone as omnidirectional antennas, they are also a building block of many other more complicated directional antennas.

- Two dipole antennas mounted at right angles, fed with a phase difference of 90°. This antenna is unusual in that it radiates in all directions (no nulls in the radiation pattern), with horizontal polarization in directions coplanar with the elements, circular polarization normal to that plane, and elliptical polarization in other directions. Used for receiving signals from satellites, as circular polarization is transmitted by many satellites.

Corner reflector - A directive antenna with moderate gain of about 8 dBi often used at UHF frequencies. Consists of a dipole mounted in front of two reflective metal screens joined at an angle, usually 90°. Used as a rooftop UHF television antenna and for point-to-point data links.

A monopole antenna consists of a single conductor such as a metal rod, usually mounted over the ground or an artificial conducting surface (a so-called ground plane). One side of the feedline from the receiver or transmitter is connected to the conductor, and the other side to ground or the artificial ground plane. The radio waves reflected from the ground plane seem to come from an image antenna below the ground, with the monopole and its image forming a dipole, so the monopole antenna has a radiation pattern identical to the top half of the pattern of a similar dipole antenna. Since all of the equivalent dipole's radiation is concentrated in a half-space, the antenna has twice (3 dB increase of) the gain of a similar dipole, not considering losses in the ground plane.

The most common form is the quarter-wave monopole which is one-quarter of a wavelength long and has a gain of 5.12 dBi when mounted over a ground plane. Monopoles have an omnidirectional radiation pattern, so they are used for broad coverage of an area, and have vertical polarization. The ground waves used for broadcasting at low frequencies must be vertically polarized, so large vertical monopole antennas are used for broadcasting in the MF, LF, and VLF bands. Small monopoles are used as nondirectional antennas on portable radios in the HF, VHF, and UHF bands.

- Type of antenna used on mobile and portable radios in the VHF and UHF bands such as boom boxes, consists of a flexible rod, often made of telescoping segments.

Rubber ducky - Most common antenna used on portable two-way radios and cordless phones due to its compactness, consists of an electrically short wire helix. The helix adds inductance to cancel the capacitive reactance of the short radiator, making it resonant. Very low gain.

Inverted F - Combines the advantages of the compactness of inverted-L antenna, and the good matching of the unipole antenna. The antenna is grounded at the base and fed at some intermediate point. The position of the feed point determines the antenna impedance. Thus, matching can be achieved without the need for a separate matching network.

- Very large wire transmitting antenna with extremely narrow bandwidth, used on VLF bands; relative to the even larger wavelengths it is used for, it is paradoxically an ultra-short antenna. Consists of a central radiating tower with multiple wires attached at the top, extending out radially from the mast and insulated at the ends, resembling a metal umbrella frame. Like other ultra-short antennas it has an extremely high capacitive reactance and minimal radiation resistance, which require a large loading coil and low-resistance counterpoise system. Used for long range military submarine communications.

Array antennas consist of multiple simple antennas working together as a single compound antenna. Broadside arrays consist of multiple identical driven elements, usually dipoles, fed in phase, radiating a beam perpendicular to the antenna plane. Endfire arrays are fed out-of-phase, with the phase difference corresponding to the distance between them; they radiate within the antenna plane. Parasitic arrays consist of multiple antennas, usually dipoles, with one driven element and the rest parasitic elements, which radiate a beam along the line of the antennas.

- One of the most common directional antennas at HF, VHF, and UHF frequencies. Consists of multiple half-wave dipole elements in a line, with a single driven element and multiple parasitic elements which serve to create a uni-directional or beam antenna. These typically have gains between 10-20 dBi depending on the number of elements used, and are very narrow band (with a usable bandwidth of only a few percent) though there are derivative designs which relax this limitation. Used for rooftop television antennas, point-to-point communication links, and long distance shortwave communication using skywave ("skip") reflection from the ionosphere.

Log-periodic dipole array - Often confused with the Yagi-Uda, this consists of many dipole elements along a boom with gradually increasing lengths, all connected to the transmission line with alternating polarity. It is a directional antenna with a wide bandwidth. This makes it ideal for use as a rooftop television antenna, although its gain is much less than a Yagi of comparable size.

Reflective array - Multiple dipoles in a two-dimensional array mounted in front of a flat reflecting screen. Used for radar and UHF television transmitting and receiving antennas.

Curtain array - Large directional wire transmitting antenna used at HF by shortwave broadcasting stations. It consists of a vertical rectangular array of wire dipoles suspended in front of a flat reflector screen consisting of a vertical "curtain" of parallel wires, all supported between two metal towers. It radiates a horizontal beam of radio waves into the sky above the horizon, which is reflected by the ionosphere to Earth beyond the horizon.

Half-square antenna - A pair of ground-isolated, quarter-wave vertical monopoles, whose tops are connected by a line one half-wavelength long. The verticals are the radiators and function as a two-element array, similar to the bobtail curtain. The structure is shaped like the Greek letter Π (not to be confused with the Half-Loop antenna described below). The top-to-top connecting wire serves as a phased feedline, or an auxiliary feed, which puts the point of maximum current at the top of each monopole. Neither monopole element has a wire connection to the ground beneath it. Top-fed monopoles produce a strong signal low to the horizon, as opposed to an ordinary bottom-fed monopoles. The feedpoint for the combined system may be placed at any of several locations.

or superturnstile - A specialized antenna used in television broadcasting consisting of perpendicular pairs of dipoles with radiators resembling bat wings. Multiple batwing antennas are stacked vertically on a mast to make VHF television broadcast antennas. Omnidirectional radiation pattern with high gain in horizontal directions. The batwing shape gives them wide bandwidth.

Loop antennas consist of a loop (or coil) of wire. Loop antennas interact directly with the magnetic field of the radio wave, rather than its electric field, making them relatively insensitive to electrical noise within about wavelength of the antenna. There are essentially two broad categories of loop antennas: large loops (or full-wave loops) and small loops. Only one design, a "halo" antenna, that is usually called a loop does not fit into either the large or small loop categories.

Large loops

Full-wave loops have the highest radiation resistance, and hence the highest efficiency of all antennas: Their radiation resistances are several hundreds of Ohms, whereas dipoles and monopoles are tens of Ohms, and small loops are a few ohms, or even fractions of an Ohm.

Large loops - are loop antennas with perimeter of a full wavelength, two wavelengths, or any whole-number multiple of a wavelength. They are naturally resonant and act somewhat similarly to the full-wave or multi-wave dipole. When it is necessary to distinguish them from small loops, they are called "full-wave" loops.

- Although "quad" can refer to a single quadrilateral-shaped loop, the term usually refers to two or more loops stacked side by side; at first glance, quads resemble a box kite frame. Only one of the loops in the quad is connected to the feedline, and that loop functions as the driver for the antenna and is the main signal radiator. The other loops are parasitic elements that act as reflectors or directors, focusing the radiated waves in a narrower, single direction and thereby increasing the gain. Quad antennas are the loop analog of antennas, and are similarly used as a directional antennas on the HF bands for shortwave communication. They are sometimes preferred for longer wavelengths because (if square) they are half as wide as a Yagi built from dipoles.

Half-loop - is the upper half of a vertical full-wavelength loop antenna mounted on the ground. The full loop is cut at two opposite points along its perimeter, and the lower half is omitted; the upper half mounted on the ground at the cut points, sticking up from the ground like a satchel handle. It is shaped like the Greek letter Π or an upside-down capital letter U, and is the loop antenna analog of a ground-mounted monopole antenna. Like a vertical monopole, the missing lower half of the antenna is replaced by its ground-plane image. If shaped like a half of a square, a half-loop can operate either as a loop antenna or, on its first harmonic, as a dipole antenna whose ends have been bent over and grounded, depending on the form and location of the feed-point.

Halo antennas - Loops that are exactly one half-wavelength in perimeter - with a small gap cut in the loop - are called "halo antennas" and are intermediate in form and function between small and large loops. They are often described as a half-wavelength dipole that has been folded into a circle, rather than being a "true loop" antenna.

Small loops

The great disadvantage of any small antenna, including small loops, is a very small radiation resistance - typically much smaller than the loss resistance, making small loops very inefficient for transmitting. However, small loops are very effective receiving antennas, especially at low frequencies, where all feasible antennas are "small" compared to a wavelength.

Small loops - If the loop perimeter is smaller than a half-wavelength, the loop must be modified in some way to make it resonant, if resonance is necessary. Small loops are called "magnetic loops", and if modified for resonance they are also called "tuned loops". Their directionality and radiation efficiency is drastically different from full-wave loops. Small loops are widely used as compact direction finding antennas.

Ferrite (loopstick) - Loopstick antennas are omnidirectional around their axes, and are premier examples of small loop antennas. They are the magnetic analogue of the short dipole antenna. These are used as the receiving antenna in most desktop consumer AM radios operating in the medium wave broadcast band (and lower frequencies). Wire is coiled around a ferrite core which greatly increases the coil's inductance and its effective signal-capturing area. The radiation pattern is maximum at directions perpendicular to the ferrite rod.

The null directions of small loop and ferrite core antennas are bi-directional, and are much sharper than the maximal directionality. This makes the direction of the null more useful than the direction of the strongest signal for accurately locating a signal source. The null direction of small loops can also be exploited to reject unwanted signals from an interfering station or noise source.

biconical antenna is a dipole-like antenna made of two cones, aligned along the same axis and oriented tip-to-tip.

discone antenna is half of a biconical with a flat disc mounted above the cone

Aperture antennas are the radio analogue of an optical telescope. They are in fact used for radio telescopes, and for general use are the main type of directional antennas used at microwave frequencies and above.

An aperture antenna consists of a small dipole or loop feed antenna embedded inside a larger, three-dimensional surrounding structure that guides the radio waves in a particular direction. The guiding structure is often dish-shaped or funnel-shaped, and quite large compared to a wavelength, with an opening, or aperture, to emit the radio waves in only one direction. Since the outer antenna structure is itself not resonant, it can be used for a wide range of frequencies, by replacing or retuning the inner feed antenna, which normally is resonant.

Unlike the above antennas, traveling-wave antennas are not resonant so they have inherently broad bandwidth. They are typically wire antennas that are multiple wavelengths long, through which the voltage and current waves travel in one direction, instead of bouncing back and forth to form standing waves as in resonant antennas. They have linear polarization (except for the helical antenna). Unidirectional traveling-wave antennas are terminated by a resistor at one end equal to the antenna's characteristic resistance, to absorb the waves from one direction. This makes them inefficient as transmitting antennas, but removes half of the incident radio noise when used for receiving.

Leaky wave - Microwave antennas consisting of a waveguide or coaxial cable with a slot or apertures cut in it so it radiates continuously along its length.

Random wire antenna - This describes the typical antenna used to receive shortwave radio, consisting of a random length of wire either strung outdoors between supports or indoors, running in an erratic zigzag pattern along walls or between supports, connected to the receiver at one end. The shape is determined by available space and supports. A random wire antenna typically will have complex radiation patterns with several lobes at angles to the wire, in different directions for each fold in the antenna. Random wire antennas typically are categorized as folded monopole antennas if their lengths are a quarter-wave or less, and end-fed dipoles if a half-wave or more, up to one or two wavelengths or less. When they are laid out with at least one fold oriented in a straight line, one to several wavelengths long, they operate similarly to traveling-wave antennas.

1. ^ Bevelaqua, Peter J. "Types of Antennas". Antenna-Theory.com. Archived from the original on 30 June 2015. Peter Bevelaqua's private website.

2. ^ Aksoy, Serkan (2008). "Lecture Notes - v.1.3.4" (PDF). Electrical Engineering. Antennas. Gebze, Turkey: Gebze Technical University. Archived from the original (PDF) on 22 February 2016.

3. ^ Balanis, Constantine A. (2005). Antenna Theory: Analysis and Design. Vol. 1 (3rd ed.). John Wiley and Sons. ISBN 047166782X.

4. ^ Severns, Rudy (N6LF) (1996). "Using the half-square antenna for low-band DXing". In Straw, R. Dean (N6BV); Roznoy, Rich (KA1OF) (eds.). ARRL Antenna Compendium. Vol. 5. Newington, CT: American Radio Relay League. pp. 35-44. ISBN 0-87259-562-5.

5. ^ Silver, H. Ward, ed. (2011). ARRL Antenna Book for Radio Communications (22nd ed.). Newington, CT: American Radio Relay League. Chapter 5, Section 9.6, Section 11.6, Section 16.5, Section 20.6, Chapter 22. ISBN 978-0-87259-680-1.

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In radio systems, many different antenna types are used with specialized properties for particular applications. Antennas can be classified in various ways. The list below groups together antennas under common operating principles, following the way antennas are classified in many engineering textbooks.

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Abstract : in this post we present a system for monitoring sudden ionospheric disturbances (SID) events. As is well known, SID events are caused by the impact with the ionosphere of solar radiation emitted during solar flares. Monitoring SID events is therefore an indirect way to monitor solar activity. SID events heavily modify the ionosphere and therefore can be detected by measuring, over time, the intensity of radio propagation in the VLF band. In our system we used the VLF receiver proposed by the UKRAA (UK Radio Astronomy Association).
Scientific Background

When a solar flare occurs on Sun a blast of intense ultraviolet and x-ray radiation hits the day-side of the Earth after a propagation time of about 8 minutes. This high energy radiation is absorbed by atmospheric particles, raising them to excited states and knocking electrons free in the process of photo-ionization. The low altitude ionospheric layers ( D and E region) immediately increase in density over the entire day-side. The ionospheric disturbance enhances VLF radio propagation. Scientists on the ground can use this enhancement to detect solar flares; by monitoring the signal strength of a distant VLF transmitter, sudden ionospheric disturbances ( SID) are recorded and indicate when solar x-ray flares have taken place.

To understand the SID effect it is essential to remember how Earths' ionosphere is created and structured. One may see the the ionosphere as a shell of electrons and electrically charged ions (atoms and molecules) that surrounds the Earth, stretching from a height of about 60 km to more than 1000 km. The main constituents of the ionosphere are neutral atoms and molecules. However, the charged nature of the ionosphere is due to production of plasma (electrons, ions) primarily by solar ultraviolet radiation. This again means that the ionosphere is 'produced' during the day and is 'reduced' during the night due to recombination processes of electrons and ions. Ionization depends primarily on the Sun and its activity. The amount of ionization in the ionosphere varies greatly with the amount of radiation received from the Sun.
The structure of the ionosphere (layers or regions) is related to the neutral gas species populating those regions and the energy of the radiation penetrating into Earths' upper atmosphere. The higher energized the radiation is the lower it may penetrate and produce electrons and ions. The electron density profile (image above) shows the different ionospheric regions during day (production of electrons) and night (recombination of electrons). The image below shows the layers of the ionosphere during night and during day.

Propagation

Effects related to terrestrial radio communication ( ionospheric or sky-waves) are due to the existence of the D and E region - also called Kennelly-Heaviside layer.

The radio signal from the VLF transmitter reaches the receiver by two paths. One of these runs along ground and is called the " ground-wave", the other is via "reflection" from the ionosphere, called the Ionospheric-wave, often known as the " Sky-wave". These two paths are of different lengths, and lead to the formation of an interference pattern. The different path lengths for the two signals means that the phases of these signals will differ at the receiver. The phase difference depends on the distance between transmitter and receiver and could lead to a cancellation or to a reinforcement.
In daytime the Sky-wave is attenuated by the absorbing part of the D-layer, while the ground-wave component of the signal progressively weakens as the receiver becomes further from the transmitter.
After dark the D-layer, which is mainly ionised by Solar Ultra Violet rays, quickly disappears and with it all the absorbing ionization. "Reflection" now occurs from the lower part of the E-layer at around 90 km to 100 km altitude. The result of this is that once the mid point of the path is in shadow at 100 km altitude, the signal strength will usually increase significantly, while the ground wave signal stays exactly the same strength. Thus night-time reception is marked by large and rapid swings in signal strength as the two, now more nearly equal strength, signals swing in and out of phase.

When Sun is active, strong solar flares can occur that will hit the sunlit side of Earth with hard X-rays. The X-rays will penetrate to the D-region, releasing electrons that will rapidly increase absorption, causing a High Frequency (3 - 30 MHz) radio blackout. During this time Very Low Frequency (3 - 30 kHz) signals will be reflected by the D layer instead of the E layer, where the increased atmospheric density will usually increase the absorption of the wave and thus dampen it, thus the Sky-wave is more powerful and lead to a rapid increase of the signal strength at the receiver. As soon as the X-rays end, the sudden ionospheric disturbance (SID) or radio black-out ends as the electrons in the D-region recombine rapidly and signal strengths return to normal.

(from http://www.inflamo.org/ and https://www.ukraa.com/)

VLF Receiver

We adopted the VLF receiver from UKRAA, which we acquired as a Kit. The assembling of the kit is simple and very well documented. We put the board, together with the antenna tuning unit, inside a metal box, as shown in the images below.

The receiver basically is a tunable audio frequency amplifier with an envelope detector. It consists of a number of functional blocks, of which the main ones are the radio frequency (RF) amplifier, the band-pass filter, the second RF amplifier, the detector and associated low-pass filter, and output buffers.
The power supply is 15 - 18 Vdc, 35mA and it has two analog output voltages with different ranges : 0-5 Vdc and 0-2.5 Vdc; we used the range 0-2.5.
The receiver has a number of other features, for details, consult the UKRAA documentation.

We describe in some details the two main block of the receiver : the RF amplifier and the band-pass filter.

The RF amplifier, scheme in the image aside, consists of an untuned cascode amplifier (tuning is done with the antenna tuning unit) with a junction field effect transistor (JFET) at the antenna input interface and a bipolar junction transistor (BJT) at the output. The cascode amplifier in this application has low gain but gain is not its only purpose. This configuration prevents antenna loading by the bandpass filter and reduces capacitance multiplication effects (Miller Effect) that would detune the antenna. The input impedance is determined by a 1 MΩ biasing resistor on the JFET gate.

After the RF amplifier there is the main block of the receiver : the band-pass filter with the main adjustments of the receiver.
The filter is a 4-amplifier biquadratic design that has the advantage of almost independent gain, frequency and Q controls. Below there is the scheme.

We will not go into details relating to this circuit configuration; it is a very selective band-pass filter whose frequency can be accurately configured using the two trimmers VR3 and VR4. With VR1 the gain of the stage is regulated, while the selectivity of the filter is regulated through its Q factor, acting on the VR2 trimmer. If Q is very high, the filter can go into auto-oscillation. The best performances are obtained by increasing Q up to obtain the auto-oscillation condition and then reducing it, by means of the trimmer, by a fraction of a turn : in this way the maximum gain can be achieved.

SID Monitoring Apparatus

The apparatus consists of a magnetic loop antenna described in detail in the post Loop Antenna for Very Low Frequency, it is a "classic" antenna that must be oriented in the direction of the VLF station. The image below shows our antenna fixed on a wooden support and positioned on a "flowered" terrace.

The antenna is connected with RG58 or RG174 50Ω coaxial cable to the VLF receiver on SMA connector. The analog output of the receiver, proportional to the signal intensity, is sent to the ESP32 module which acquires the signal, converts it to digital and sends it, via WiFi network, to the Raspberry PI which performs the storage, processing and display of data on graphic as shown in the post DataLogging with ESP32 Module. The image below shows the receiver and the ESP32 module.

VLF Stations

With an SDR (software defined radio) receiver and an up-converter we verified the VLF signals present in our area. We have considered the frequency band up to about 40 KHz; the spectrum is that represented in the image below, obtained with the SDR # application.

Among the various emissions, we have identified three VLF transmitters that can do for us : this is the All these broadcasters are mainly used for radio communications with submarines, since VLF waves can penetrate many meters below the surface of the sea. 26.7 KHz signal emitted by the antennas of the
The 26.7 KHz emission, located at 1500 km, is the best candidate, albeit more distant and therefore weaker, to display more clearly the propagation of the radio signal in correspondence with solar flares.
The following maps show the location of the three selected VLF transmitters. Bafa transmitter in Turkey located about 1500 km; at a shorter distance, about 800 km, there is the 21.75 KHz transmitter of the HWU system located in Rosnay in France; at an even shorter distance, 560 km, we find the 20.76 KHz frequency of the Tavolara transmitter in Sardinia.

Quiet Sun

The chart below has been recorded at 26.7 kHz, from the Bafa transmitter in Turkey. This graph shows signal strength against time over a 24 hour period. It shows random variation in signal strength at night, followed by a change (decrease) as the rising sun recreates the D-layer. During the day, signal strength varies with the altitude of the Sun. At sunset, the D-layer recombines and is lost, producing another change (increase) in signal strength.
This trend is quite typical for a "quiet sun" situation.

Unfortunately our environment and our homes are saturated with electromagnetic disturbances and we have to live with. often in our graphics we will discover interferences such as the one shown below : we must get used to them and not confuse them with real solar flares !

Solar Flares

The first M class flare of the "new" solar cycle n.25 was detected by our system on 05/29/2020 ! The sun is currently going through a period of minimum activity, but there are the first "signs" of the new solar cycle. On 29/05/2020 an active sunspot zone gave rise to a series of class C and class M flares, detected by our VLF receiver. The image below shows the graph of our receiver and the graph produced by the GOES X-ray satellite. The main four flares can be identified.

References

UKRAA site : https://www.ukraa.com/
Application of the UKRAA Very Low Frequency Receiver System - Reeve

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VLF Receiver for SID Monitoring - PhysicsOpenLab

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Abstract : in this post we present a system for monitoring sudden ionospheric disturbances (SID) events. As is well known, SID events are caused by the impact with the ionosphere of solar radiation emitted during solar flares. Monitoring SID events is therefore an indirect way to monitor solar activity.

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Solar flares and their effects on the Earth's ionosphere

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Solar flares and their effects on the Earth's ionosphere

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DIAS (Dublin Institute of Advanced Studies)Astrophysics & Astronomy Seminar presented by Laura A Hayes and hosted by Dr. Peter Gallagher (DIAS & I-LOFAR).

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Dublin Institute for Advanced Studies DIAS

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Solar Flares and their effects on the Earth's ionosphere

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Sample data collected using Pictor and Stellarium

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Data collected by students over a 10 month period.

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Sample data collected from Pictor telescope

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This activity sheet allows students to calculate the measurements needed to build the horn antenna including the antenna length, waveguide dimensions and dimensions of the pyramidal flared horn. It includes instructions on the construction.