The first test to see the coherence of two rtlsdr in realtime consist in do a cross-correlation of the two dongles, the cross-correlation is a measure of similarity of two signals.

To do the test I used baudline and tuned to a local VOR/DME. Here in the first picture can see some coherence of the two dongles using one antenna to every rtlsdr:

RTLSDR baudline cross-correlation with 2 antennas

Here the result if disconnect one antenna:

RTLSDR baudline cross-correlation with 1 antenna disconnected

After the nice videos that Juha Vierinen has shared, looks that some people is interested in use multiple rtlsdr coherent for radar applications for example. I’m starting my experiments with this setup:

RTLSDR Cohernt setup

My setup consist in two rtlsdr dongles with r820t tunner with the xtal removed, connected to a PTS-160 Synthsesizer tunned at 28.8 MHz and locked to 10 MHz GPS reference.

SDR & RadioAstronomy rack

With coherence using radar mehtods, you can get cool images like: