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Old 26-01-2023, 04:41 PM
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Malewithatail (Dick)
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Anyone here interested in radio astronomy ?

My interest in radio astronomy dates from high school. Whilst all the other boys were making garden forks and other bits n pieces in metal work, I was making yagi aerials that operated at 220 MHz. Taking them home in pieces in my school bag. I'm sure the teacher had no idea what I was doing, and as I kept to myself, he had bigger issues to look after. I eventually made 4 off, 24 element yagis out of what was then 3/4 inch flat bar, with folded dipoles and a phasing harness. Two in series, with 2 in parallel, giving the required 300 ohm feed-line impedance as the set required. 75 ohm impedance's were not yet common place.

My receiver was a highly modified old Pye tv set, chosen from the scrap heap as it had 5 intermediate frequency amplification stages and was a super fringe set. I re-tuned the IF strip for maximum audio gain as the video output was of no concern.

I mounted the aerials of broom handles, lined up using a long piece of timber and swept the setup across the sky.

My first hearing of the suns noise hooked me for life.

I graduated to a 3 meter aluminum dish, which I transported home on the roof of my old truck, on bits of timber, yes 3 meters wide on the road !! Then came F to D ratios and other stuff.

After cascaded valve rf amplifiers came gasfets, supposed to be the cats whiskers of amps, but oh so noisy, then cmos devices, darlintons, and experiments with cryogenic cooling of cascaded j-fets using liquid nitrogen obtained from the lab at work.

Whilst still at school, I became involved with the Ilawarra Amateur Radio club and the moon-bounce project at Dapto, led by Lyle Patterson. I can still hear the echos of our own signals from the moons surface. We had a high power permit to run 1 kilowatt on the 433 MHz ham band. Now hams do Venus and Mars bounce, such is the technology available nearly off the shelf now.

Somewhere I still have some of the gear Id collected to do this, but the technology has outpaced hi powered tetrode valves, klystrons, Traveling wave tubes and the like now. All museum pieces, rather like myself !!


Looking into the infinite makes you realize just how small we actually are.



Surprising results are possible even with old Austar dishes and analogue set top boxes, slightly modified to receive ssb with an external BFO.


'nuff for now.


Dick
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Old 26-01-2023, 05:06 PM
LonelySpoon (Neville)
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Hi Dick,
I've played with RTL-SDR in the 1420MHz range, and with Radio Jove dipole observations of Jupiter/Io. Both systems are languishing since I moved house.
I have got a set-up almost ready for FM meteor 'watching', though.

I've also made a horn receiver with aluminised foam insulating panel as well, and currently there is an old Foxtel dish on the deck waiting for more spare time than I have.

I always figured that if it was too cloudy for optical, I could switch over to radio, but that would probably cause an earthquake or something to occur.

Real problem is that the electronics, for me, has to be purchased, not made, and my budget currently points elsewhere.

Neville
LSO
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Old 26-01-2023, 09:49 PM
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Stonius (Markus)
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I think it's pretty amazing the stuff you managed to assemble in your high-school days. How did you learn enough to know what you were doing without the assistance of the internet? I'd like to learn about this stuff, but wouldn't even know where to begin, so hats off to you! Thanks for the post.
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Old 01-02-2023, 06:12 PM
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Malewithatail (Dick)
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No one else I knew was doing anything like that, but the closest was the Moonbounce radio group at Dapto.


The receiver isn't too hard to design, a SDR with an high gain pre amp will do, even a decent scanner with a pre amp will give results. Especially on sun noise.


That said, a dedicated design with a proper narrow band front end and low noise cascaded, double balanced mixer, would be needed. I do have a homemade double balanced mixer receiver, and I first thought it faulty when I made it as there was absolutely no noise from it when I switched it on. After some hours checking and rechecking, I decided to connect an aerial to it and see if a signal could force its way through. When my ears recovered from the cacophony of stations, I realized that I had been tricked by the very characteristic of a double balanced mixer, lack of conversion noise as its cancelled out in the miser stage. My receiver has no RF amp stage, so is a bit 'deaf' but works well enough and uses only 3 easy to get integrated circuits, no surface mounted bits and is built on a perfboard, not even a circuit board.


I may design a cascaded RF amp stage, along with an outboard attenuator and filter, and have another go, but with the coming world problems, astronomy, and radio in general, is on the back burner.


The intermediate stage would need some more rejection as two tuned circuits aren't enough and there is some 'double spotting' on strong signals.


I seem to remember that a frequency of around 20 megahertz was optimin, and also for Jupiter around 22 megs was a good place to start. The signals sound like an electrical storm on earth, with frequent crashes and bangs. It is a rather wide band, for space exploration, signal, but much narrower than a normal broadcast station, and more difficulty is added because the signal drifts around quite a bit, so some form of adjustable oscillator, tuned by the signal strength may be needed, its possible a phase locked loop would do it, with the phase being fed back into the oscillator from the biggest noise level.


Then there is the matter of an aerial, 'cause at 20 megs, 1/2 wavelength is 10 meters, so a tuned dipole would be 20 meters long and need to be steerable, unless a fixed aerial was used and the timing of the planets rise above the horizon calculated for the location etc.


Thanks for replying, at least someone is watching !!
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Old 01-02-2023, 08:05 PM
croweater (Richard)
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I'm watching too mate but sadly most of it is way over my head. Interesting stuff though and thanks for posting.
Cheers, Richard
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Old 03-02-2023, 08:06 PM
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AussieSky (Greg)
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I've been playing around at 1420 Mhz since about 2007 and have posted a few messages here, but no-one has been interested except a few overseas colleges and Uni's, who are currently using the equipment.
http://www.gco.org.au/SRTInfo/srt.html


Greg
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Old 04-02-2023, 08:43 AM
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Still getting used to navigating the site, hello mate. Withe current technology, old Auststar dishes and a decent LNB will get one started. I have so much to do that one lifetime isn't gunna be enough !
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Old 04-02-2023, 09:02 AM
LonelySpoon (Neville)
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I've got the small Foxtel dish, but I'd really like to get a mesh 2-3m sized dish. Missus wasn't impressed with the idea of it cluttering up the place in Sydney, but now we've moved...

I was offered a 3m solid dish from an ACT radio station but it'd be too heavy to mount.

My plan is to use an old trailer axle I've got as an English Cross type mount.

Neville
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Old 04-02-2023, 10:13 AM
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Make sure the f to d ratio is suitable for the frequency you want to use, to set the LNB in the right position. A terrestrial satellite dish isn't quite right, but will work. I had a 3 m aluminum dish at the other farm, and its f to d ratio was quite shallow, it worked OK, not optimin but it did work.



Here is how to measure it for prime focus


https://www.titaniumsatellite.com/do...ll%20Guide.pdf


https://www.glossaria.net/en/satelli...atio-and-depth
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Old 04-02-2023, 06:53 PM
jamespierce (James)
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I have a couple of dishes - Main one is a 4.5m dish with quite a fine mesh which I use for 23cm amateur radio moon bounce. I always intended to do some Ha radio astronomy with it when I get bored of bouncing signals of the moon (The novelty has not worn off yet! Still remarkable every time).
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Old 05-02-2023, 08:15 AM
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I was involved with the IARS radio club and the Dapto moonbounce project at 432 megs, using a dish provided by the Wollongong university. That would have bee at least 50 years ago !
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Old 05-02-2023, 08:21 AM
jamespierce (James)
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Quote:
Originally Posted by Malewithatail View Post
I was involved with the IARS radio club and the Dapto moonbounce project at 432 megs, using a dish provided by the Wollongong university. That would have bee at least 50 years ago !
The efforts using the Arecibo dish on 70cm are legendary also - all before my time unfortunately. It's amazing to think that it was only first successfully done in 1946 by some American DARPA types...

I've made successful contacts using ~1W of power - speaks to how far our electronics and DSP software has come. I always marvelled at how we received signals from Voyager II way way below the noise floor at parks, and just integrated enough signals to pull it out - now we do the same thing at home.
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Old 05-02-2023, 04:40 PM
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Malewithatail (Dick)
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All the gear at Dapto was initially valve (Tube) based, I remember the first solid state transistor "samples" we got for the front end. Amazing in the late 60's to have a transistor that worked at 440 megs, without needing liquid nitrogen. Only we were throwing several hundred watts at the moon and getting maybe 1 watt reflected back to us.


The Wollongong Uni supported the group with the building and some equipment as well as machining services for feed horns etc.


Lyle Patterson, VK2ALU was the leader, and the call sign used was, I think, VK2AMW, Amateur Radio Wollongong. Too long ago, almost a lifetime in the past ! I have trouble remembering what happened this morning, let alone 60 years ago ! I also remember how cold it was in that building without heat etc, in the middle of winter. Tuning up on sun noise and waiting for the moon to rise. Hearing your own signals a second or so later was a kick as well, all CW, no voice, and manually tuning the receiver to cope with the moons relative motion and the Doppler effect. All so simple now with SDR's and computers. I suppose its the same with optical, all so simple with CCD cameras and computer driven mounts. The dish drive needed 3 phases, 415 volts ac, and also the main drive motor was a wound rotor type, needing resistors in the rotor to control the speed. All good stuff, and seat of the pants observing.


Its easier now, but do you learn as much ? Probably not, as its all been done and if you have the dosh, you can go and buy the gear to do it.


Never did get my 3 meter dish working properly as the F to D was all wrong for the frequency and the focal point was too far out. The dish was too shallow for 440 megs operation, the wavelength was too long. Nowadays, probably 10 gigs would work, and I seem to remember some experimentation at 10 gigs from Dapto just before it closed down. Gunn diode detectors and so on.
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Old 05-02-2023, 09:05 PM
jamespierce (James)
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"If I have seen further it is by standing upon the shoulders of giants"
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Old 06-02-2023, 07:47 AM
LonelySpoon (Neville)
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Dick, I understood all of those words but about half of what was said!

I vaguely recall reading about the moon bounce episode in Electronics Australia, if that is what it was called then. My school used to get them, and Scientific American.

Heady days for science and astronomy and far less loonies!

Looking at two weeks of rain here so might get the horn out again and play with it, and the NOAA gear.

Neville
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Old 06-02-2023, 10:00 AM
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I was posting about my radio-astronomical project 10 y ago...


https://www.iceinspace.com.au/forum/...d.php?t=113407
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Old 06-02-2023, 04:37 PM
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Malewithatail (Dick)
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My Dapto moonbounce posts were in the late 60's early 70's. My own setup was when I was in High School in the late 60's.
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Old 07-02-2023, 12:43 PM
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http://www.iars.org.au/wp-content/up...983-10-Oct.pdf
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