Crude SDR radio telescope

[Astronomist]

Way Back in February I built this Radio telescope for the school science fair. I  meant to post it here for a while, but never got around to it until now. The dish was 1.5m diameter (it split in two in order to be car portable), constructed from surplus thin Corex sheet over a frame of scrap 1/8" ply. It was then covered in extra-strong tinfoil. The feed antenna was a biquad design. I did not use a hydrogen line bandpass filter due to the low budget nature of this build, the electronics were as follows:

antenna - LNA - LNA - RTLSDR dongle - laptop running SDR sharp

The dish was not made to very tight tolerances, and thus probably close to the performance of a satellite dish of half its aperture, but it worked fine for my purposes, i did manage to detect the hydrogen line, which was cool.😀

some of you may notice I wrote this post in the past tense as after the science fair i broke it up because i couldn't store it long term. There may be a mk2 at some point, but with a bandpass filter and proper satellite dish. Heck, i might even build a mount for it!

Edited August 25, 2023 by Astronomist

[Alex_Fla]

Do you have any data you could post ?

The biquad feed with its open ends allowed the loops to receive ground temperature noise,

and the proximity of the PC may have added RFI, but overall a very good effort !!

If you want to try something again, consider this  : It works reasonably well, is no more difficult to fabricate

than your Science Project, is low cost and  quite portable...

 

Regards,

Alex

Winter Springs Fla

 

[Astronomist]

I will have a look and see if I still have some screenshots of the data, I am fairly sure it was the hydrogen line as I got a nice hump in the IF average spectrum on several occasions peaking around 1420.5 MHz (this was with the dish pointed into the milky way in the Cygnus region). The PC was not always as close as it is in the picture, I had to use a USB extension cable on the dongle as I did experience issues with noise. I also wrapped a piece of tin foil around the LNAs, not sure it made a lot of difference though.

I like the loop feed, if I do build another i will use one of those instead of a biquad. I never thought about using an umbrella as a dish, that sure would have saved me a lot of work. 

[Alex_Fla]

A Photo Umbrella's shape is a very poor 'parabola'.

What it does have is a Deep shape that blocks the 290K radiation from surrounding ground/trees/buildings and provides a bit of RFI shielding. Also, it is easy to fabricate.

Your Reflector is (was) a superior design. but perhaps a bit shallow .. If You Do plan to make another one,  work toward an f/D  ratio of 0.3 to 0.35 .

For a more detailed video of my RT development :

Regards,

Alex

 

 

Edited September 10, 2023 by Alex_Fla

[Alex_Fla]

Too bad you trashed the reflector .. With a new feed and a nooelec SAWBird H1 you might have been impressed with its Performance !

Also, Dish <> Feed spacing is quite critical . With my 1.2m system, a shift of 5mm is quite measurable  !

Alex

[Astronomist]

It took me a while to get around to it, but I have searched my hard drive and cannot find my data screenshots. I don't remember deleting them so probably they are in some obscure folder with a non-descriptive name. I hope they aren't in my 'lights' folder. I'd never find them among 16000 pictures of the moon.