Hackaday has brought to attention a tutorial written on the Raspberry Pi forums by Sonny_Jim showing how to decode pager transmissions on the Raspberry Pi. In the tutorial he also shows how to set up a web server to be able to view the decoded transmissions in a web browser.
He uses a RTL-SDR and Raspberry Pi and pipes the output of rtl_fm into the multimonNG software to decode the messages.
Over on Reddit user olgierd has posted a video on this thread showing his work on developing a portable software defined radio based on an RTL-SDR R820T, the rtl_fm software and a Raspberry Pi with LCD screen. The software is based on rtl_fm which has the capability to demodulate FM/AM/SSB signals. His video shows him tuning to various signals using a tuning knob.
Note that his setup is capable of playing the audio, but it is not shown in the video as he only had earbuds connected. In the future he hopes to make it more portable by adding a li-ion battery.
YouTube user 907h9879070g9790 has posted a video showing Virtual Radar Server running on a Raspberry Pi with the Raspian hardfloat image OS installed. He used Mono to allow the .NET based Virtual Radar Server to run on the Raspberry Pi. Instructions for using Virtual Radar Server with Mono can be found here.
Combined with an rtl-sdr and dump1090, ADS-B packets can be sent to Virtual Radar Server, and then the aircraft radar map can be viewed on a PC or internet enabled device via a network connection. This can allow a small self contained remote ADS-B monitoring system to be set up.
EDIT: Unfortunately the video owner has taken down the video.
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.
