RTL-SDR vs. AIRSPY on ADS-B Reception: Round 2
A few days ago we posted about Anthony Stirk’s comparison between the RTL-SDR and the Airspy on receiving ADS-B signals. In his first test Anthony used an E4000 dongle, which is known to have inferior performance at the ADS-B frequency of 1090 MHz.
Now Anthony has done his test again, but this time with an R820T2 RTL-SDR. His results show that the R820T2 RTL-SDR is better than the E4000 RTL-SDR, but that the Airspy is still better than the R820T2 RTL-SDR. The R820T2 received at maximum distances more comparable to the Airspy, though still fell short of the Airspy by some 50 kms in some directions. Anthony’s writes that his distance seems to be mainly limited by geography so it is possible that in some other location the Airspy could out perform the RTL-SDR by a more significant distance.
The most interesting part of his last experiment was that over a 28 hour period the E4000 RTL-SDR received only a total of 2.9 million messages whilst the Airspy received a total of 10.3 million messages. In the new experiment the R820T2 received a total of 22.3 million messages whilst the Airspy received a total of 31 million messages, which is a little closer. However, with the R820T2 RTL-SDR, 3 million messages were unusable, versus only 31 unusable messages with the Airspy.
From these results it’s clear that the better design and more ADC bits in the Airspy can significantly improve ADS-B reception. However, there is a cost difference at $199 for the Airspy vs <$20 for the RTL-SDR. The Airspy cost may be soon less of a problem we are aware that an Airspy Lite version is in the works and that will probably cost around $99 USD.
In the future Anthony will do another test with no error correction enabled because the current version of the Airspy ADS-B decoder has no error correction whereas the RTL-SDR ADS-B decoder does. Those results may show that the Airspy is even better that shown here.
Update: Anthony ran the test again with a modified version of ADSB# with not error correction and obtained the following results which show that the Airspy receives about double the messages compared to the RTL-SDR:
Total Messages Received:
What is the street address of Airspy?
Out of interest, has a control experiment been run with coax splitter outputs and feeders reversed to rule out any power mismatch feeding the different units under test – it’s unlikely to be exactly 3dB split. If not, it may be worth a look and averaging the results?
Could be also interesting to see AirSpy vs HackRF. If I need to spend 199$ for a 24 – 1800 MHz only RX I prefer add 100$ and I have a 10 – 6000 MHz RX and TX.
HackRF isn’t a very good receiver, it’s probably only about as good as the RTL-SDR, or maybe even a little worse. You buy the HackRF for the TX capabilities and think of the RX as a bonus. If you want good RX performance then i’d say go for the Airspy or SDRPlay.
I’ve added the results of a further test done with the RTL. Youssef Touil kindly supplied a version of ADSB# with duplicates suppressed, with the equivalent of dump1090’s –no-fix and with no phase “enhancement” that produce CRC valid noise. This provided a direct comparison with the Airspy.
tl;dr Airspy does twice the messages of the RTL in a like for like situation.