[HN Gopher] Designing a Home Radio Telescope for 21 Cm Emission
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Designing a Home Radio Telescope for 21 Cm Emission
Author : antognini
Score : 47 points
Date : 2024-11-04 18:21 UTC (4 hours ago)
(HTM) web link (arxiv.org)
(TXT) w3m dump (arxiv.org)
| emptybits wrote:
| Page three of the paper shows an enviable rooftop antenna farm.
| Drool.
|
| I have an ignorant question ... can home/amateur radio astronomy
| ever produce layperson-appreciated "imagery"? Something easily
| understood like optical astronomy can produce? e.g. stitching
| together a sky scan for a particular emission or something?
| radioguy22 wrote:
| Yes. But nowing a bit of signal theory, hf electronics and
| embedded is super helpful.
|
| With 2 antennas you can start playing around with beam forming.
| This will enable you to scan the sky from one position without
| moving the antenna. Then you can map the signal strength to a
| sky projection.
|
| Have a look at the low-frequency antennas from LOFAR. They look
| like tents for chickens. A lot of them.
|
| It sounds complex and yes.. it's also a bit complex. But still
| in the range of a project for the home lab.
| RedOrGreen wrote:
| Yes, in a way.
|
| Think of a single dish radio telescope as a one-pixel camera,
| where measuring the emission intensity at each point in the sky
| lets you build up a map. Typically, this is done with high
| resolution on the frequency axis, which is used to map Doppler
| shifts for spectral lines of Hydrogen, for example [1].
|
| With a rooftop antenna, it's not likely to be a very sensitive
| map, though. You'll see the Sun, and its easy to see the Milky
| Way transit overhead, but other than that ...
|
| [1] https://sites.google.com/site/galfahi/
| wbl wrote:
| Thanks to the rotation of the earth and antenna fixed in one
| direction sees a bunch of the sky over an evening.
| spacedcowboy wrote:
| Yep "drift scanning" :)
|
| A single dish/node can't really produce photograph-like
| imagery akin to an optical telescope, more often[1] you get
| something like in the setileague website hits [2].
|
| [1] Where by "more often" I mean "once in a blue moon".
|
| [2] http://www.setileague.org/photos/hits.htm
| spacedcowboy wrote:
| I had a dish set up in London, 20 years ago (before I came out to
| the USA). Looked like #1. The dish splits into segments, and I
| recall driving down the M1 from Birmingham in my battered old
| Ford Escort, with the (razor-sharp) mesh segments squeezed in and
| wobbling right next to my jugular... Those dishes were getting
| vanishingly hard to find in the UK, so it was worth the trip, and
| I kept my neck intact with only minimal damage...
|
| I had it all packed up when moving out to the US (because my
| imagination told me that houses in the US were far larger than in
| the UK). The house I ended up buying (despite having a much
| larger back garden) didn't have the space to set it up again and
| remain married, so two decades later, it's still in that wooden
| case... I do, however, have an optical telescope set up (#2)
|
| Back then, we didn't have easy access to SDR's, so there's a feed
| horn, a down-converter, and I had an external (standalone)
| WinRadio receiver to actually listen to the feed. That went into
| an audio card on a linux box, and the waterfall display was
| beautiful :)
|
| #1: https://imgur.com/a/CDrEeII
|
| #2: https://imgur.com/a/askar-130phq-scope-sb-myt-mount-26mp-
| cam...
| radioguy22 wrote:
| The RTLSDR is a great tool. But signals really be bandpassed
| (what the guy in the paper did) because its dynamic range is
| limit to only 8 Bit.
| mhh__ wrote:
| The german Wurzberg radar system
| (https://en.wikipedia.org/wiki/W%C3%BCrzburg_radar) was used
| after the war to help discover the hydrogen line.
| bloopernova wrote:
| I've just started learning about radio comms. I'm using the ARRL
| Handbook for Radio Communications 101, which is great so far.
|
| My main goal is to detect the hydrogen line, or maybe some
| distant/noisy object (can amateurs pick up pulsars?). I also want
| to understand antennae much better, and maybe make a wire fractal
| antenna. I have a crazy idea about making a 3D fractal antenna-
| making bot from Lego or something! :D
|
| (I'm not under any illusions about whether a fractal antenna is
| "better" but I just like the idea of them)
| radioguy22 wrote:
| Start detecting signal reflections from airplanes.
|
| With multiple synchronized receivers you can build a passive
| radar.
|
| Single reflections can easily be spotted by just staring at the
| spectrum (Doppler).
| Enginerrrd wrote:
| I'm super into this idea as a project, can you point me to
| any design or signal processing info?
| kortilla wrote:
| A lot of passive radar stuff is ends up export controlled
| so open source is sparse here
| hatsunearu wrote:
| Of note is that this is a high school paper.
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(page generated 2024-11-04 23:00 UTC)