AirSpy vs FA SDR with Parallel RF Path
I set up parallel systems to compare the performance of a 12 bit AirSpy mini and an 8 bit RTL-SDR.
A normal FA omni antenna feeds a cavity bandpass filter and then an LNA. From there the RF signal is split in a microwave power divider with > 25 dB isolation between the 2 output ports. One port drives the AirSpy, the other the RTL-SDR.
The two SDR dongles each are connected to two Raspberry Pi 3B+, each running 3.7.1. Each of the two Pi is connected via Ethernet for FA access.
The gain settings for each SDR were adjusted over time to maximize the received signal count.
The Airspy averaged about 1400 messages / second in busy times, while the RTL-SDR tended to run about 1100 at the same times.
I plotted the total aircraft count for the two systems for several months. The Airspy side consistently performs better in both total message count and total AC seen.
Here’s a 30 day snapshot of aircraft counts:
The AirSpy channel has about 6% more aircraft on average.
I’ve since shut down the parallel path and the AirSpy channel performance has improved some more. Power supply noise reduction at the LNA seems also to have helped by about 1%.