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

Jiao Xianjun putaoshu at
Thu Jan 2 13:25:45 UTC 2014

I see some UDP packet performance issues in my laptop (but not in my desktop computer). Will the common (interleave multiple receives) UDP link helps?

The issue is that fread for the second dongle in matlab get less data than expectation sometimes. Seem that fread for the first dongle works well.

-----Original Message-----
From: "Sdr Guru" <sdrguru1 at>
Sent: ‎2014/‎1/‎2 5:39
To: "osmocom-sdr at" <osmocom-sdr at>
Subject: Re: How to get IQ samples from multiple rtl-sdr dongles in asynchronized manner?



Some of the recommendations.

Please add PPM error calculation, exactly like new rtl_test -p but multiple receivers simultaneously.
It provides immediate information if something is wrong with USB or dongles.

Please add automatic eeprom PPM calibration

default sample rate 2.4M (28.8/12) or 1.2M (28.8/24), probably lower jitter
MAX_NUM_DEV 4->16 :)

Some nice to have features.

ip binding

multicast support

one common (interleaved) stream of all the receivers
timestamped stream

I'm trying to convert MATLAB script to Ocatve.


On Mon, Dec 30, 2013 at 9:38 AM, Jiao Xianjun <putaoshu at> wrote:

Hi guys,

For the multiple dongles synchronization in signal level instead of bits/packets level, I setup a working repo in github, and write a initial demo framework. See below:

You may find information and instruction of demo quickly by reading the README.

My initial purpose is performing in-fly calibration for multiple dongles according to some pre-known signal (GSM, ADS-B?) to let them work together coherently.
An ideal scheme may be that we should generate a very narrow band and very week signal in (or just located at the edge of) target working band of dongles, and perform the software in-fly calibration in background (or driver level). This would be user friendly.

I know it is far from final state currently, and many things are not clear yet (See TODO). But please join me if you also think this is a good idea. Just check out the demo and run it to have a look.
Currently I just test the demo in Ubuntu-Linux.
Jiao Xianjun
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