How to get IQ samples from multiple rtl-sdr dongles in asynchronized manner?

Leif Asbrink leif at
Mon Dec 30 15:09:03 UTC 2013

Hello Jiao,
> My thought is doing the compensation by software according 
> to a common source over the air instead of over the hardware.
> Do you think it is doable? 

Yes. This is most certainly possible. The same thing was done long
ago in radio astronomy. Two big telescopes on different continents
made recordings aiming at a coomon direction in the sky. By
evaluating the recordings they could make interferometry.

This is a very interesting approach for the future.
With several dongles that have some signals in common it
will be possible to synchronize in software.

One of the common signals could be a GPS diciplined frequency
standard that the software could use to provide extreme 
frequency stability on the processed signals from all the dongles.

Once syncronization is arranged one could use the multi-channel
antenna for interference suppression and to improve S/N of any
desired signal.

> And what would be the bottleneck according to your experience? 
There is a lot of code that has to be written, but
I do not think there is any bottleneck to worry about
in hardware

> Any possibility to tune the hardware by software after we 
> estimate the synchronization error in frequency and timing?
The entire passband of the dongles will be coherent.
You can tune to any frequency within the passband and also
evaluate several frequencies at the same time.

In case one wants to change the center frequency one would
loose synchronization and one would have to restart the
synchronization procedure.

SDR has just begun. Most of the interesting things have 
not yet been done:-)


Leif / SM5BSZ

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