ADS-B experiences

After two months of experimenting with a generic SDR dongle, a dedicated ADS-B dongle and a couple of antennas, here’s my experience so far.

 

Used equipment:

  • FlightAware Pro Stick Plus
  • NooElec NESDR SMArt
  • FlightAware antenna (66 cm)
  • Magnetic ground plane antenna
  • Telescopic FM antenna
  • Raspberry Pi 3B+ (Piaware image)
 

In order of importance, expressed in an (approximated) percentage of influence on my ADS-B reception, this is what helped to improve my FlightAware feeder statistics:

[70%] – Antenna placement. Outside is better than inside (obviously), especially for houses with energy saving windows (metal coated glass reduces signal strength ~40%). Higher is better, in general, but it pays off to experiment:

  • Raising my outside antenne by 80 cm, as well as increasing its view angle by 2 degrees, made it receive more aircraft – but at the cost of most of its >400 km reception…
  • My inside antenna turned out to perform much better after moving it from the window to a wall, where an obstacle outside did no longer block a high air traffic area.
  • Since ADS-B is basically a ‘line of sight’ transmission, it’s clear that obstacles can block signals. But they can also act as rear view mirrors! A large apartment building that blocks my long range reception in one direction compensates for this by bouncing signals from an otherwise completely blocked direction.  

[20%] – Antenna type & quality. The FlightAware antenna isn’t cheap, but its 5 dB gain will extend your reception range compared to simple 1/4 or 1/2 wavelength antennas.

[5%] – Dongle. The FlightAware Pro Stick Plus squeezed a bit more out of all tested antennas. And it didn’t get as hot as the NooElec.

[5%] – Cables & connectors. Use quality cables and keep them as short as possible. Also: periodically check your SMA and/or N-type connections (they can get loose over time).

Tip 1: The amazing Virtual Radar Server (VRS) software is extremely useful for finding the best antenna position. It can create receiver range plots over time, even for different altitude ranges. This allows for a visual comparison of different antenna positions and choosing the one that fits your needs (i.e. best coverage of a particular area, best long range reception, etc.)

Tip 2: Experiment with your receiver’s gain. This is a setting in dump1090 (the demodulator/decoder software component). Default setting in the Piaware image is ‘AGC’ (Automatic Gain Control), that is supposed to dynamically adjust gain in order to avoid ‘clipping’ of the strongest signals. However, some reliable sources claim it will set gain to ‘max’ (49.6 dB) …

If you have ssh enabled on Piaware, here’s the commands to read the current gain setting:

sudo systemctl status dump1090-fa -l

To set gain to, for instance, 40.2 dB:

sudo piaware-config rtlsdr-gain 40.2

Make sure to restart the dump1090 process for your changes to come into effect:

sudo systemctl restart dump1090-fa

Possible gain values are: 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 and 49.6

Note: supplied values will be rounded to the closest value in the list. A value of -10 will set the receiver in AGC mode.