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

Sylvain AZARIAN sylvain.azarian at
Sun Aug 25 15:30:34 UTC 2013

Another issue you'll have is to start both dongles simultaneously...
with the sampling rate you'll have on the dongles this becomes quite tricky
: you get blocks of samples from both dongles but you have no idea of how
many samples they are shifted in time. One way to solve this is to search
for cross correlation between channels, but this is not very easy in
realtime. This can be done by post-processing offline.
I thaught of this a while ago, using a pin diode or something equivalent to
shortcut both inputs to ground to find an easy way to have the synchro
between channels but did not try it yet


2013/8/25 Jiao Xianjun <putaoshu at>

> basically you are right.
> But there is signal processing algorithm to track two dongles
> sampling/oscillator error separately and compensate them separately. Thus
> we can get them synchronized finally after signal processing algorithm.
> What I need actually is that how to get two streams of sample from two
> dongles.
> Actually I notice that in dump1090 it put rtlsdr_read_async in a new
> created background thread, then there is a possibility that I create two
> thread to operate two dongles. But in this method, there should be some
> mechanisms to synchronize two threads. It is complicated.
> Anyone has simpler solution?
> Thank you.
> On Sun, Aug 25, 2013 at 9:49 PM, Thierry Leconte <
> thierry.leconte at> wrote:
>> Le 25/08/2013 15:13, Jiao Xianjun a écrit :
>>  Hi,
>>> I want to use multiple rtl-sdr dongles to do some multi-antenna
>>> experiments.
>>> Is it possible to read IQ samples from multiple rtl-sdr dongles in a
>>> synchronized manner?
>>>  Each dongle have its own clock, so it will never be synchronized at the
>> sample level.
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