YouTube user nerdsville shows a signal reception comparison of his discone antenna and his home made 1090 MHz tuned ADS-B collinear antenna in this video. The collinear antenna shows a dramatic improvement over the discone.
ADS-B is a broadcast system which can be used to track aircraft like a radar. More information about rtl-sdr and ADS-B here.
Blogger John Wiseman has managed to get ADS-B decoding using an rtl-sdr stick working on his AR.Drone quadrocopter. The AR.Drones run on the Linux operating system, so he was able to compile and install the Linux ADS-B decoder dump1090 on his drone.
Although the reception was hampered by RF interference from the drones electric motors, it was still able to pick up a number of ADS-B signals.
The RTL-SDR can be used as a super cheap real time air radar. Modern planes use something called an ADS-B (Automatic Dependent Surveillance-Broadcast) Mode-S transponder, which periodically broadcasts location and altitude information to air traffic controllers. The RTL-SDR can be used to listen to these ADS-B signals, which can then be used to create your very own home aircraft radar system. Compared to dedicated commercial ADS-B receivers which can go for between $200 - $1000, the $20 RTL-SDR is very attractive for the hobbyist in terms of price. However, note that the RTL-SDR probably shouldn't be used for ADS-B navigation in a real aircraft for safety reasons.
ADS-B broadcasts at a frequency of 1090 MHz. It has been discovered by the RTL-SDR community, that the RTL-SDR with R820T tuner has the best sensitivity at this frequency. The E4000 and other tuners perform poorly in comparison. So it is recommended that you obtain an R820T tuner if you want to set up ADS-B decoding with the RTL-SDR. Recently there has also been talk about the R820T2 tuner, which seems to have slightly better performance too. See the Buy RTL-SDR dongles page for more information on where to purchase.
We also now note that recently new higher end SDR's like the $199 Airspy have developed very good ADS-B receivers that are several times more sensitive that the RTL-SDR.
In this video, YouTube user Superphish shows a timelapse of air traffic over New Zealand using RTL-SDR, ADSB# and Virtual Radar Server.
