RTL-SDR for Radio Astronomy-Planning


Recently I designed a semi-permanent balcony mount for my GOES16 satellite dish. Last year, I was able to receive images over a ten minute period just balancing the dish, but this time I was able to download for hours on end. Receiving those images from 42000Km in space was truly amazing. It brought we back to a time when I was a teenager following all the Apollo missions. While I was receiving the images, it suddenly occurred to me that perhaps my dish could receive other signals from space, such as pulsars or planetary emissions. There are many excellent YouTube videos on Radio Astronomy using simple equipment (Ref.1).


Fig.1 GOES16 SAWBIRD LNA/BPF Frequency Response
Fig.2 GOES16 Satellite Dish with NanoVNA SWR Sweep
Fig.3 GOES16 Satellite Dish NanoVNA SWR Sweep Response

I decided my first project would be to receive the so called “Hydrogen Line” at 21cm or 1420.405MHz (Ref.2). This is caused by a spin flip transition between the hydrogen electron from one state parallel to the proton and one state anti-parallel to the proton. These waves are very useful as they penetrate the massive amounts of interstellar dust that block ordinary light.

My hope was that I could use my GOES16 satellite dish and LNA/BPF for reception at 1420MHz since this is relatively close to 1694MHz. In order to test the SAWBIRD LNA/BPF, I connected it directly to my SignalHound Spectrum analyzer with a whip antenna. The wideband receive white noise acts as a sweeping signal and the response is shown in Fig.1. The bandwidth is approx 85MHz, but only starts at 1640MHz. So this will not work in this application. I noticed that there was a particular SAWBIRD designed for the hydrogen line, so I ordered one. The next test was to sweep the dish with the NanoVNA to see what the VSWR looks like. My version of the NanoVNA only goes up to 1.5GHz, so I swept from 1000 to 1500MHz. There is a nice dip in VSWR (4.2) at 1420MHz, so I think the dish may work.

Software Windows10

Fig.4 Equipment/Software Block Diagram Win/RPi
Fig.5 SDRangel Setup/Device=RTL-SDR/RxPlugin=Radio Astronomy

Figure 4 shows the proposed equipment/software configuration. Signals will be received on the satellite dish and directly feed a 1420MHz SAWBIRD LNA/BPF. This will then feed an RTL-SDR with biased T to power the LNA. Signals will be decoded by SDRangel using the Radio Astronomy Rx Plugin as shown in Figure 5.

Fig.6 YouTube Video RTL-SDR for Radio Astronomy – Planning
YouTube Channel
YouTube Channel


#1. – “Scanning the Galactic Plane”, Kevin A. Wilson

#2. – “Hydrogen Line”, Wikipedia

#3. – “SDRangel”,

By Jeremy Clark

Jeremy Clark is a Senior Telecommunications Engineer and Advanced Amateur Radio Operator VE3PKC. He is the author of E-Books on Telecommunications, Navigation & Electronics.