IOR1: Radio telescopes by Graham Woan

Small Angle Formulae

2024-09-23 12:01:44 UTC

Why are the small angle formulas used even when the angles are not small, surely that makes it less accurate?

Hello Professor, where can we find the recordings of the lectures?

2024-09-25 17:23:39 UTC

Can something be a blackbody and not have a Planck Spectrum? if so what are some examples?

2024-09-30 12:49:38 UTC

Directional antenna

2024-09-30 17:40:57 UTC

What does it mean for an antenna to be more directive? And is this always a positive?

Brightness Temperature

2024-10-02 12:07:05 UTC

Is the brightness temperature the same as the effective temperature that we've seen in SSE last year. As in the temperature of a black body which produces the same luminosity as the source being observed?

Q10 Question Sheet 1

2024-10-09 11:45:41 UTC

Where does this relationship between temperature and solid angle come from?

Solid angle

2024-10-14 18:22:21 UTC

I’m not 100% certain how the expression for solid angle is obtained, though I may be overlooking something obvious !

Question sheet 1, question2

2024-10-29 14:52:47 UTC

Im just wondering for q2, if you could explain how we obtain the units for the flux density of the sun? I've tried to work it out just from their SI units but cant quite get it to be Wm^(-2)Hz.

Question Sheet 1 8b

2024-11-02 12:43:51 UTC

To determine the beam solid angle from the gaussian power pattern, how do we integrate the gaussian and what are the limits of integration?

Question Sheet 2 Question 2

2024-11-03 08:59:34 UTC

Hi, I'm just wondering if this is a type of question that would come up in an exam or if it's more to aid understanding? I can slightly understand (visually) the relationship between different antenna patterns and power patterns, and can follow the logic to the solution, but really struggle to come up with the functions themselves and couldn't have worked out this result mathematically. Is there somewhere I could look for more examples like this where the functions themselves have to be calculated? Thank you for your help

Phase-switched interferometer

2024-11-09 15:56:19 UTC

Hi there, just wondering if this is something still covered by the course? I came across it in the exam questions but I can't find it in the lecture slides. Thanks!

Exam questions Q6

2024-11-21 19:48:32 UTC

Hi there, please could you explain how you go from the right hand side of the top line to the right hand side of the lower line? Thank you very much in advance

Derivations

2024-11-22 12:50:08 UTC

Would it be possible to be provided with a list of which derivations we are expected to know, and where possible could we have a copy of these as handwritten notes. However, i understand that this might be too much to ask for.

Such as for sheet 1, question 6 & 7, within the video solutions are brilliant, because they show clearly what level of detail and explanations we would be expected to show :)

How does this allow is to define a normalised power pattern?

2653059c — 2024-12-10 11:18:44 UTC

Relative Difficulty of Exam Questions vs Question Sheets

2024-12-10 19:12:44 UTC

Hello! I have noticed that the question sheets seem to be more difficult in comparison to past exam papers, is this due to the fact that we can use our notes for question sheets?

Question 8b QS1

2024-12-17 12:14:36 UTC

Hi, could you go over this step in a bit more detail? Specifically where the term in front of the exponential goes from steps 2 to 3?

Simple 2-Element Interferometer

2025-01-20 16:50:34 UTC

Hello :)

On slides 70-71, there is a derivation step I don't understand.

How do we get from the iky and ika phases in the diffracted (complex) wave line to those in the intensity line?

I have tried many trigonometric identities and am sure I am making a silly mistake somewhere, so would appreciate some guidance :) thanks!

Question Sheet 2 Q8

2025-02-05 16:57:16 UTC

The Fourier transform of the first function is not immediately clear to me. I first separated the function B(theta) into a term dependent on alpha and beta which required me to multiply out the brackets of B(theta). this led to the required fourier transform for the theta dependent term however for the beta term I obtained a factor of (beta^2)/2 in the exponential instead of beta/2.

Correlating Interferometer

2025-02-07 15:40:37 UTC

Hello prof. Woan, I was wondering why the mixer comes before the filter in a correlating interferometer, while the filter comes before the mixer in a total power telescope.

Sheet 2 question 6

2025-03-19 13:44:27 UTC

The solution refers us to handout 2. Does this mean that the content in these handouts is examinable in addition to the lecture slides?

Sheet 2 Q7

2025-03-19 21:48:19 UTC

The solution states that the baseline vector for the north-south orientation is (0,D,0) but the slides indicate that the a direction is north so wouldn’t this be (0,0,D)?

How do you convert from rads^-1 to Hz?

2025-04-01 10:30:31 UTC

Interferometers insensitive to changes in gain and system temperature

2025-04-14 11:46:40 UTC

I'm slightly confused about how the noise voltages averaging to zero means that the interferometers are insensitive to changes in gain and system temperature? Could you maybe expand on this relationship. Thanks

Equation Sheets

2025-04-18 09:34:14 UTC

In the A345HM general information page there is an equation sheet provided for each astro course. The sheet provided on this moodle is vastly different to that provided by yourself on the IOR moodle page. I also assume the standard integrals you included on your sheet would be given in an exam if relevant anyway. Can you please clear up which will accompany our exams.

2019 paper

2025-04-21 09:37:36 UTC

Would the comments in brackets be required for all 3 marks?

question sheet 1

2025-04-24 10:30:13 UTC

For question 9 when computing the antenna temperatures, there is an equation in the slides which gives Ta = AeΩaTb/ƛ^2 (part 2. slide 31), why does this equation give a different answer for antenna temperature compared to that in the solutions video?

question sheet 1 qu 3

2025-04-24 14:13:12 UTC

within this question, would the units on B not be W/m^2/Hz/sr as we converted converted S to W/m^2/Hz from Jy before popping it into the calculation for B

problem sheet 1 qu 9

2025-04-24 16:05:13 UTC

when finding the power, can we just use power=kT(bandwidth), which does give the same numerical answer

can we make that assumption of T_A being true temp with source as a blackbody, fills beam etc?

2019 3(c)

2025-05-02 14:29:37 UTC

Hi there, please could you explain how the final factor of w appears in the denominator of the final line? Is it just by matching the square of V(s) to the question by assuming there is some normalisation factor? Thank you very much in advance for your help!

Paper 2023 Q3)d)ii)

2025-05-07 09:23:14 UTC

Hello, I was just wondering if it would also be correct to write N=7 for the seven antennas and work out 21 baselines, explaining that the 'blob' is from the short baselines, or if it makes more sense/would have to be N=5 for the sites. Thank you in advance!

Temperatures

2025-05-07 15:25:05 UTC

Hi there, I have became confused about the difference between brightness temperature and antenna temperature can you please explain how these are different and the different circumstances that you would use them

Question Sheet 2 Q11

2025-05-08 15:53:42 UTC

Hi I'm slightly confused about the method used in part (c) of question 11. My main issues are:

1) I get an extra factor of 2 when rearranging for the perigee speed (I'm sure I'm being really silly but I just can't tell where the halves go in the energy equation)

2) I'm slightly confused on why we are just the bandwidth frequency to get the wavelength (which gives a wavelength of 18.75m) but then we use the wavelength for the 22GHz? I'm guessing the 22GHz is the correct frequency to use in this case but I just want to double check

3) Could you maybe explain why using the Doppler shift gives the fringe rate? (I know the maths is gone over in Q10 but I'm slightly confused about the concept)

Thank you so much!!

Question Sheet 2 Q12 (a)

2025-05-09 09:45:36 UTC

Hi I'm not quite sure what's going on in this final normalisation step. Could you maybe explain how the P(0,0) condition leads to this normalisation coefficient? I can't seem to get P to be 1 at theta = 0 under any circumstances, I just get that P is zero. Thanks!

2019 Q3)c)

2025-05-11 09:54:50 UTC

Hello, I was just a bit confused as to why the exponent here is positive? As, in the exam equation sheet, the Fourier transform formula is a negative exponent? I was just wondering how exactly the form of the FT given in the exam equation sheet is converted to this one? Is it because of converting from path difference to phase difference? Thank you so much in advance!