Introduction
In the previous three posts I looked at my receiving equipment used for GOES16, to see if I could re-purpose it for reception of the so called hydrogen line at 1420MHz/21cm. I checked the dish for VSWR (Ref.1), and tested the LNA/BPF (Ref.2/3). The final step was to orient the dish for maximal reception of the Milky Way and perform a signal capture. There are several excellent articles/videos describing the procedures involved (Ref.4). Various authors recommend the Open Source software Stellarium for location of the Milky Way (Ref.5). In particular, there is a step by step tutorial for using an RTL-SDR + Dish + LNA/BPF (Ref.6).
Since I am not an astronomer, and this being a totally new area for me, it was tough trying to identify the H line signal. I spent a whole week orienting my dish in different directions (and all hours!) trying to capture a signal generating portion of the MW. My initial fear was that a spurious product received earlier (1420.8MHz) would overwhelm my reception when I connected the dish. Fortunately this didn’t occur. What did happen was that I received a wide band comb of components which was disconcerting. This happened when I pointed the dish due south 45/90deg and east 45/90deg. When going up/down in frequency by 10MHz the components disappear. I will have to try a different location outside of my urban area to get reception.
The Milky Way in Stellarium
Stellarium is a pretty amazing program, it also comes with a user guide pdf. The first thing I did was set my default location in the location window on the left hand side menu. Following the tutorial, I disabled the day time atmosphere by pressing “a”, then set the Milky Way brightness to “6” in the sky & viewing menu. This clearly shows the current location of the milky way in the sky from your default location. Figure 1 shows the appearance of the Milky Way from my location in Toronto looking south east.
Performance of LNA/BPF + Dish
I was curious to see how well the dish was working at 1420MHz. So I did the same random noise test that I did with the LNA/BPF (Fig.2). First I measured the wide band noise performance of the LNA/BPF with an open input (Fig.3), then with the dish attached (Fig.4). You can see a noticeable gain (approx. 20dB).
Signal Capture Attempt on SDR#
During the past two weeks I experimented with various methods of signal capture. I followed the tutorial (Ref.6) and used SDR# with the IF Averaging Plug-In. Figure 6 shows reception centred at 1420.405MHz showing the comb signal. Figure 7 shows the spectrum after averaging out the background. The spurious are so strong that even after averaging the hydrogen line signal is not visible. I am going to move the equipment to a different location preferable out of the city to take another signal capture.
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References
#1. – “Radio Astronomy LNA/BPF Testing with NanoVNA”
https://jeremyclark.ca/wp/telecom/radio-astronomy-lna-bpf-testing-with-nanovna/
#2. – “RTL-SDR for Radio Astronomy – LNA/BPF Testing”
https://jeremyclark.ca/wp/telecom/rtl-sdr-for-radio-astronomy-lna-bpf-testing/
#3. – “RTL-SDR for Radio Astronomy – Planning
https://jeremyclark.ca/wp/telecom/rtl-sdr-for-radio-astronomy-planning/
#4. – “RTL-SDR Blog Articles Hydrogen Line”
https://www.rtl-sdr.com/?s=hydrogen
#5. – “Stellarium Astronomy Software”
http://stellarium.org/
#6. – “Cheap and Easy Hydrogen Line Radio Astronomy with ….”
https://www.rtl-sdr.com/cheap-and-easy-hydrogen-line-radio-astronomy-with-a-rtl-sdr-wifi-parabolic-grid-dish-lna-and-sdrsharp
