Airspy have recently released an update to their ADSBspy decoder, which is an Airspy One/R2 compatible decoder for 1090 MHZ ADS-B signals. According to 'prog', the software developer of ADSBSpy, his setup can see almost double the number of aircraft and with fewer false positives when using the updated software. Prog writes that the secret to the improvement is some reworked DSP code that aims to exploit oversampling in the Airspy to the maximum.
We compared the new (184.108.40.206/39) decoder against the old decoder (220.127.116.11) which used to get similar performance to dump1090. The test setup was two Airspy dongles connected to a dipole antenna via a splitter, with our Triple Filtered ADS-B LNA used by the antenna. One Airspy was used to power the LNA via it's bias tee, and both units received the same amplified signal. We found indeed that the new version of ADSBSpy receives a good number more aircraft in our set up, and an increased number of ADS-B messages too.
It seems that most of the additionally received aircraft must be from extremely weak signals, because when looking in Virtual Radar Server the extra aircraft usually only show their ICAO and maybe altitude and speed until they get closer.
So far this software appears to provide the best performance on ADS-B that we've seen so far, so if you are using an Airspy for ADS-B tracking we'd like to hear results from anyone who upgrades.