ADS-B decoding allows you to receive GPS and other information from aircraft in your vicinity. We also have a tutorial about ADS-B decoding available here.
The BeagleBone Black is a small embedded Linux computer, similar to the Raspberry Pi. It has enough computational power to run the RTL-SDR and ADS-B decoder.
Over on YouTube user Adam Alicajic has uploaded a video showing how coax cable loss affects the frame rate when receiving ADS-B. To do this test Adam uses a precision attenuator in between his ADS-B antenna and RTL-SDR dongle to simulate attenuation from coax cable loss. His results show that for every 1 dB of attenuation the frame rate drops by about 10%.
Coax cable loss for common type of cable can be estimated with calculators available at http://www.net-comber.com/cable-loss.html and http://www.arrg.us/pages/Loss-Calc.htm. RG-6 cable has a low loss at 1090 MHz of about 0.23 – 0.32 dB per meter, whereas RG58 has a loss of about 0.5 – 0.6 dB per meter and RG174 (stock antenna cable on most RTL-SDR units) has a greater loss of about 1.2 dB per meter.
Coax length loss contribution to the bad ADS-B reception
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: Airspy 65,150,313 RTL 32,973,049
Airborne Position: Airspy 4,615,972 RTL 2,270,810
Unusable: Airspy 533 RTL 635,549
Airspy vs R820T2 RTL-SDR on Maximum ADS-B Distance.
With the recent release of ADSBSpy, an ADS-B decoder for the Airspy software defined radio, many people have been wondering how much better the Airspy is compared to the low cost RTL-SDR dongle at ADS-B reception. Over on his blog, Anthony Stirk has performed a test comparing an E4000 RTL-SDR with the Airspy.
In his test Anthony uses an A3 ADS-B antenna from Jetvision.de, and a HABAMP which is an LNA plus 1090 MHZ SAW filter. To create a fair test he used an antenna splitter and measured the reception of both dongles at the same time. He ran one instance of ADSB# for the E4000 RTL-SDR, and one instance of ADSBSpy for the Airspy over 24 hours and recorded the results.
Airspy vs E4000 RTL-SDR
The results showed that the Airspy had approximately 50 km more range compared to the E4000 in some areas. More interestingly the stats showed that the Airspy received approximately 7 million more ADS-B messages compared to the RTL-SDR.
While there is no doubt the Airspy will perform better, one thing to note about this test is that it used an E4000 RTL-SDR which is widely considered to have inferior performance at the 1090 MHz ADS-B frequency when compared to the R820T/2 dongles.
The author’s tutorial goes over setting up ModeSDeco2 to broadcast data over the network, setting up ModeSMixer2 to receive data, and also setting up the basestation.sqb file to add airline logos and silhouettes to the web based GUI of ModeSMixer2.
Previously we posted about Android programmer Tosis Nikolaos’s last app which was called “Track your flight Europe”. The app allows you to view aircraft tracked via ADS-B received by an RTL-SDR on an offline map.
Now Nikos has written into us once again to let us know about his new app called “Track your flight North America“. It is the same as his previous app, but this one has high resolution offline maps for North America. He also writes that his Europe app has also been updated to support high resolution offline maps. The app costs 5.09 Euros + VAT. To run it you will need an Android device and an RTL-SDR with OTG cable.
Over on the SonicGoose.com blog, the author has recently created a tutorial showing how to use Modesdeco which is a multi platform command line ADS-B decoding software application. ADS-B stands for Automatic Dependent Surveillance Broadcast and is a signal broadcast by aircraft that can be used to track them like a radar.
Modesdeco is a command line ADS-B decoder quite similar in purpose to other software like dump1090, RTL1090 and ADSB#, however it has more available features built into it. The blog author writes about Modesdeco:
Want to feed BaseStation and PlanePotter at the same time? No problem. Want to add another data stream for Virtual Radar Server? No problem. Want statistics about the types of data being received? No problem. Want to run it on a variety of platforms, including Windows, Mac OS X, Linux, or the RaspberryPi? No problem.
The author’s tutorial goes over setting up the software on Windows and turning on some features like it’s web statistics interface, interactive map and how to feed data to another virtual radar application like Basestation. In the future the author plans to write a second tutorial showing how to use another feature which allows a user to combine the ADS-B feeds from various computers running Modesdeco.
Screenshot of the Modesdeco statistics web interface.
In most of the world aircraft use the ADS-B standard for location tracking which transmits at a frequency of 1090 MHz. However, in the USA there is the option for aircraft to instead use the Universal Access Transceiver (UAT) protocol which transmits at 978 MHz.
UAT has some extra features for pilots compared to ADS-B. In addition to location information UAT provides a Traffic Information Service (TIS/B) which allows pilots to see what ground control sees on their traditional RADAR system. It also provides a Flight Information Service-Broadcast (FIS/B) which includes weather and other information. It seems that most small aircraft in the USA prefer to use the UAT system due to it’s lower cost and additional features.
