adsbox adsb receiver antenna rtlsdr gain

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As adsbox did take too much CPU from my main server I moved adsbox to a banana pi zero w. Running Raspbian adsbox used about 200% of the 4 cores and 10% of the 512 MB headless system. That was OK for me and I wanted to extend the range of my rtlsdr antenne. I moved the antenna out side and was impressed about the exended range but nearby aircrafts did not show any more 🙁

As I want to see the nearby aircrafts, we are near düsseldorf in the landing lines and wanted the data of the aircrafts crossing the small home village 30km away from the DUS airport.

adsbox missed too much data or the rtlsdr dongle received too much signals. First I changed the adsbox call to use 4 threads for adsb decoding. That did not help.

Then I looked for the gain values to lower the reception signal strength. My rtlsdr RTL8232u supports gain values (found with rtl_test):

#Supported gain values (29): 0.0 0.9 1.4 2.7 3.7 7.7 8.7 12.5 14.4 15.7 16.6 19.7 20.7 22.9 25.4 28.0 29.7 32.8 33.8 36.4 37.2 38.6 40.2 42.1 43.4 43.9 44.5 48.0 49.6

I first started with 0.0 and got better nearby results but only a range of about 5km. Using 25.8 gives a range of 120km but too much airplanes (~39) and nearby losts. With the max gain I had more than 59 airplanes at a time. Finally I used 16.6, which still gives a range of 80km and ~5-10 airplanes.

Using the highest gain would give a very large range of ~250km but nearby signals get lost. And we ant to see mainly the nearby airplanes and now use a gain of 16.6.

The cpu usage is now down to 100% (quad core, so that is 25%) and the adsbox decocde threads are down to 15-25%.

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