Recent Talks from the Society of Amateur Radio Astronomers 2023 Conference

Over on their YouTube channel there have been numerous talks uploaded over the past few months from the 2023 Society of Amateur Radio Astronomers (SARA) conference. Some of these talks are quite useful for beginner radio astronomers who are getting started with small dishes and software defined radios like the RTL-SDR.

One talk by Alex Pettit describes how to build a radio telescope from a an umbrella and some "Faraday fabric" which is copper cloth. The results show more than adequate performance for the cost, making this an affordable and easy entry to radio astronomy.

Alex Pettit - Umbrella Antennas

Another video presented by Dr. Wolfgang describes building small to medium sized radio telescopes. He explains how small radio telescopes less than 3 meters in size can work well for receiving the 21cm Hydrogen line, and how SDRs are the best choice of receiver for them. Many examples of small dish installations are shown.

Dr. Wolfgang Herrmann: Building Small/Medium Size Radio Telescopes

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Also a diy fabric antenna for QO100 using beachball:


Alex Petit saying he invented it but there’s that Brit guy selling them on ebay for a few years now.


Please provide a link to the Ebay site. Thanks !


I doubt you will find this 21cm umbrella antenna system elsewhere described ..It is the result of several years of research, testing, and optimization of ~1 meter sized hydrogen line radio telescope antennas. It incorporates a tuned 1.42GHz loop feed and closely coupled LNA.


Typical Performance


ebay link is here 👍


Listing was first posted in 2020

Screenshot 2023-09-15 at 20.31.33.png

nanovna swr & logmag looks favorable

Screenshot 2023-09-15 at 20.32.51.png

The reflector is very shallow The helix feed is thus exposed to picking up ground noise. That will greatly reduce the S/N of the system . The plus for the photo umbrella is the deep dish shields the feed. The 1.7GHz antenna might work, but I recommend building the system designed for 21cm.

If you have the 1.7GHz antenna, Try it and compare. I’d be interested in seeing the results.


The dish shields the feed …


The importance of reducing antenna “Spillover” ( in this case ground noise reception ) can not be overemphasized. Especially for small systems which can not use large choke-ring beam shaped feeds, minimization of having the feed not ‘see’ the ground/buildings/trees etc is important. Attached graph : On my 1.2 m system, Cold Sky power level is 7.2 dB lower than the Ambient Temperature Ground and surrounding objects. Restated : the RF Noise Power from Ambient Temp objects is 5X higher than Cold Sky.


Thanks for the link.. That will not work well for the low level signals of hydrogen line emissions. 1) the ‘parabola’ is way too shallow thus exposing the feed to ground noise 2) the feed is a helix which also is not optimal for H1…


Hi Alex, didn’t this guy here try using a standard umbrella lined with rf fabric just last year. In his article he is saying the umbrella is too deep and inefective. Read here




The Link did not work… Yes, a photo reflector is a poor excuse for a Parabola. But perhaps 1/2+ of its diameter is okay. Their value is that its deep and minimizes ground noise. The only properly shaped fold-able Parabolic Antenna for 21cm of which I am aware is from Paul @ Sub Lunar Systems.. but they are in the $1K+ range.


This is data from a 1m Faraday fabric lined photo reflector .. With a properly tuned feed it Does work ..


Those “Brit guys” get all over the place!


Coming to Hollywood i heard too.


Thanks for the information, I never knew about their YT channel.
Many hours of interesting content.
Excellent reporting work RTL-SDR blog.