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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!

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From the worked solutions for this question

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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!

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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!!

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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

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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!

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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!

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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?

:)

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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

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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?

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

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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.

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Interferometers insensitive to changes in gain and system temperature

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Interferometers insensitive to changes in gain and system temperature

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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

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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)?

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

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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.

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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.

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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!

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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?

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Relative Difficulty of Exam Questions vs Question Sheets

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Relative Difficulty of Exam Questions vs Question Sheets

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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?

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

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

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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 :)

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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

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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!

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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

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

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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.

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

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

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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?

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

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

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

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

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

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