Over on YouTube we’ve discovered a video from earlier in the year showing the RTL-SDR being used as a passive aircraft radar. This is different to ADS-B which is a type of active radar. A passive radar works by using a very strong radio signal from a readily available source such as a TV or FM radio transmitter and detecting the reflections from aircraft.
A RTL-SDR based passive radar system can be built by connecting two RTL-SDR dongles to a single clock source and by using two directional antennas.
We’ve also posted about RTL-SDR based passive radar being used to track aircraft here and here in the past. Another post about coherent multichannel RTL-SDR receivers can be found here.
Juha Vierinen from the Kilpisjarvi Atmospheric Imaging Receiver Array has been working on a Dual Coherent Channel RTL-SDR modification. This modification essentially involves using the same clock source for two RTL-SDR dongles, which can be done by desoldering and removing the clock on one dongle, and then using a cable to connect the clock from another dongle to the clock input of the desoldered dongle.