RTL-SDR for Radio Astronomy – EM Interference


In the previous four posts I looked at re-purposing my receiving equipment used for GOES16 for reception of the so called hydrogen line at 1420MHz/21cm (Ref.1/4). I found that reception from my home location was not possible due to heavy interference or intermod. I did a brief study to get a handle on this. First I used a wide-band log response amplifier to get an idea of the received RF power in the 900 – 2400MHz bandwidth. I then checked the local catv/internet feed to see what it looked like, and finally I went to the park behind my apartment building to see what I received there. I found the local wide-band power was very high at -34dBm. The local catv signal did not have any components above 1.2GHz so that was ruled out. There was a very strong comb like signal picked up in the park at 1440MHz.

EM Interference Broadband Detection

Fig.1 EM Broadband Detector Block Diagram 900MHz – 2400MHz
Fig.3 Local CATV/Internet Cable Spectrum

I used a wide-band RF detector as shown in Figure 2 to measure the total received RF power in the bandwidth 900 – 2400MHz. It is based on the AD8313 log amplifier (Ref.5). The reading peaked on the 6th LED which corresponds to -34dBm which is quite high, meaning a hot EM environment. I also checked the local catv/internet feed to see if there were any potential components in the 1420MHz area. There was nothing above 1200MHz.

EM Field Interference

Fig.4 Strong Comb-Like Signal at 1440MHz Received NTPark

Figure 4 shows the strong comb-like signal received at the park just adjacent to my location. It has the same needle like structure seen on the interference signal. So this is a prime suspect!! Further investigation is needed.

Fig.5 YouTube Video RTL-SDR for Radio Astronomy – EM Interference

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#1. – “RTL-SDR for Radio Astronomy – Signal Capture1”

#2. – “Radio Astronomy LNA/BPF Testing with NanoVNA”

#3. – “RTL-SDR for Radio Astronomy – LNA/BPF Testing”

#4. – “RTL-SDR for Radio Astronomy – Planning

#5. – “AD8313 Data Sheet Analog Devices”

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.