Arrays of dishes or other 1420MHz antenna - are they worth it?

[andrew....@googlemail.com]

Hi All,

Is it possible to create an array of dishes? I don’t mean an interferometer but combining 2 or more dishes to create an effectively bigger telescope?

If so, is this a difficult thing to do and is it worth doing?

Andy

[Marcus D. Leech]

Things like YAGI arrays are done all the time.  Often in a N x N arrangement, with appropriate combiner hardware
  to produce a good "aggregate" pattern.

I think the problem with combining dishes is that the ideal "stacking" distance for multiple antennas is typically
 less than 2 lambda between each antenna.   At 21cm, you can see that would be hard to achieve with dishes...

Once you move to a spacing of more than two or three wavelengths, you're basically building an adding interferometer,
  with the attendant grating lobes.

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[Nathaniel Butts]

In one of our on-line meets (don't remember which, atm), we were discussing Ted's plans for a patch yagi array using disk shaped reflectors.  There was a question an interferometer would allow for better resolution in the H1 band and I believe the consensus was interferometers would only allow better resolution of point sources, not for continuum sources like the H1.  You won't necessarily create a bigger telescope, but you would, by adding the signals together in an adding interferometer, increase the received power from H1.

So I guess (and correct me cause I'm likely wrong) it is a simulating a larger antenna because it is more sensitive due to the collection power, but also not a larger antenna because it does not decrease your beamwidth?

When I get my current scope performing like I want, I'll be building a similar patch yagi, cause it seems really neat.

Thanks,

Nathan Butts

Wannabe Astronomer

Bowling Green, KY

[Andrew Thornett]

It sounds like there is far more to be gained by adding antennae together to make array than an interferometer, as this will give better resolution and sensitivity similar to bigger antenna - or have I got that wrong?

What I have difficulty working out is how, in an array as opposed to interferometer,  the coaxs from individual aerials are connected to each other. Do you just solder coaxs together from each aerial?

Andy

Sent from Outlook for Android

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From: sara...@googlegroups.com <sara...@googlegroups.com> on behalf of Nathaniel Butts <nathani...@gmail.com>
Sent: Tuesday, November 28, 2023 5:43:07 PM
To: Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Subject: Re: [SARA] Arrays of dishes or other 1420MHz antenna - are they worth it?

 

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[bsn...@gmail.com]

You might want to read Wolfgang Herman's essay on antennas: "Part 4: Observation Results with Different Antennas" in the May-June 2019 issue of SARA.

In fact, all four parts are worth reading if you haven't already done so.

....bill....

[tedcl...@gmail.com]

Yeah, good stuff from Wolfgang and the Astropeiler "Hydrogen Team".
I think that is the #4 of the 4.

See
      https://groups.google.com/g/sara-list/c/W_vF2twRsCA/m/N4YVOwkWAQAJ

      (speaks of "2008", but meant "2018" ?)

which links to
      https://www.astropeiler.de/en/beobachtungen-der-21-cm-linie-mit-einfachen-mitteln/

---
Ted Cline   N0RQV

[fasleitung3]

Am Dienstag, den 28.11.2023, 17:39 -0800 schrieb tedcl...@gmail.com:
>
>
> https://groups.google.com/g/sara-list/c/W_vF2twRsCA/m/N4YVOwkWAQAJ
> (speaks of "2008", but meant "2018" ?)
>

Yes indeed, it meant 2018. In 2008 I did not do radio astronomy
yet.....
Wolfgang

[bsn...@gmail.com]

Part 1: Nov-Dec, 2018, Introduction & overview

Part 2: Jan.-Feb., 2019: Low Noise Amplifiers and Filters

Part3: March-April, 2019:Receivers and Software (Backends)

[Paul Maxan (microp11)]

I found this link and the exercise very interesting:

https://public.nrao.edu/interferometry-explained/

[Randall Wayth]

Hi Andy,

Yes, it is possible to combine signals from dishes in the analogue domain, but there are many caveats of course. To your second question "is it worth doing?". The answer depends on what you're trying to achieve and what sources you want to observe. To your subsequent question about just soldering the coaxes together, the answer is absolutely no. At the very least you need a power combiner, but really it comes back to what your goal is. 

In order for an analogue-combined array to work you will need to compensate for the delays between dishes. If your array is only ever pointing in one direction, this can be done in principle with approapriate lengths of coax before a power combiner as well as ensuring the gains of all the analogue paths are the same.

It would be much easier thesedays to do this digitally, and in fact building an array with digital backend gives you the same (and more) information than what you would get with an analogue combined back-end. The HERA radio telescope is an example of an array with fixed (zenith-pointing) dishes, but like all modern radio telescopes, it has a digital back-end.

Cheers,

Randall.

[Andrew Thornett]

Thanks Randall - that is a brilliant explanation, really helpful. Thanks for taking the time to write it so clearly.

Andy

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Sent: Thursday, November 30, 2023 2:12:19 AM

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Subject: [SARA] Re: Arrays of dishes or other 1420MHz antenna - are they worth it?

 

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