Nice. Now the question is how accurately you can timestamp the ADS-B replies. If you can timestamp them to within a few hundred nanoseconds, and have at least three (preferably four) receiving stations networked, you can draw a radar picture of your local airspace.
The problem are the RTL2832U receivers.
The sample rate is too low, 500ns resolution with 2MSample/s is not enough.
For this reason I cannot recommend using the dvb-t sticks as ads-b receiver (the symbol rate is too high, compare nynquist theorem).
Multilateration has already be done for ADS-B on large scale, but with different receivers.
There are receivers available[1] with nanosecond accuracy (and gps time synchronization).
GPS synchronization isn't needed, by choosing other flight paths to provide basic time synchronization between receivers.
Given that UmTRX is dual channel, has a GPS locked clock and is much higher performance is general, I'm thinking it might make for an excellent platform for experimenting with passive RADAR!
I'd like to know, but I'm not sure it is possible with a USB SDR stick. My solution in build is to use a high sample rate stereo soundcard with one channel capturing the audio from an analogue receiver and the second capturing a GPS time sync pulse.
