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

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Jiao Xianjun putaoshu at gmail.com
Thu Jan 2 12:09:56 UTC 2014


Good to know that. Actually I also notice that radio astronomy is
attracting more and more signla processing researchers to work on it. Some
conference, such as ICASSP, envn setup a dedicate session on radio
astronomy. There is a radio astronomy called "DOME" are carrying on, which
involves computation on massive data and signal processing algorithm.

You have notice the problem that re-tuning will casue lossing
synchronization. That's also the problem I considered.

Because we always want the rtl-sdr work in the band we are interested, but
unfortunatelly in that band there maybe no any pre-known reference signal
for us to do synchronization. So a possible solution maybe make a beacon,
which can generate ultra-narrow-band or ultra-low-power signal in the
target band to help us do the on-line calibration. Any better ideas to
avoid this dedicate beacon?


On Mon, Dec 30, 2013 at 11:09 PM, Leif Asbrink <leif at sm5bsz.com> wrote:

> 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.
>
> http://en.wikipedia.org/wiki/Very-long-baseline_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:-)
>
> Regards
>
> Leif / SM5BSZ
>
>
>
>
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