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(a)laposte.net&gt; wrote:

computer has become more powerful than our imagination. According to my experiences, order of Msps correlation operation can be done in real time by using state of art computer. Instead of cross correlation, we can also transmit a training sequence (for example spread code, m sequence, barker sequence, M sequence, ZC sequence, etc.) to do synchronization and sampling/frequency correlation. On Sun, Aug 25, 2013 at 11:30 PM, Sylvain AZARIAN &lt;sylvain.azarian(a)gmail.com > 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 > > sylvain > > > 2013/8/25 Jiao Xianjun &lt;putaoshu(a)gmail.com&gt; > >> 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(a)laposte.net>> >>> 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. >>> >>> >>> >> >

Hi, Yes, you are right. The thought is kind of message combination or information fusion, diversity receiving. In this situation, large distance spaced antennas/dongles are required to get enough diversity. But in some application, such as beam forming, direction finding, we want to have antennas/dongles located in a strict relation ship, such as lambda/2 spaced antenna array. In this case we want to detect carrier phases of each channels. On Mon, Aug 26, 2013 at 12:11 AM, Skip Tavakkolian < skip.tavakkolian(a)gmail.com&gt; wrote:

Hi, Looks interesting! Can you give more details ? (specially on the processing behind) ? regards sylvain 2013/9/2 Sdr Guru &lt;sdrguru1(a)gmail.com&gt;

Thanks. sylvain 2013/9/2 Sdr Guru &lt;sdrguru1(a)gmail.com&gt;

Hi Are you using a common clock? http://kaira.sgo.fi/2013/09/16-dual-channel-coherent-digital.html I've modified some of the RTL dongles, played with GNURadio and Octave. The results are promising, sample level correlation (2.4M/10, FM radio signal). On Mon, Dec 30, 2013 at 9:38 AM, Jiao Xianjun &lt;putaoshu(a)gmail.com&gt; wrote: Cheap (8USD+PP), simple, computer-controlled and legal FM band "marker" http://blog.palosaari.fi/2013/08/naked-hardware-12-usb-audio-transmitter.ht… I know it is far from final state currently, and many things are not clear Testing it and I'll let you know.

Hi Thanks for youar advices. I will check them as soon as possible. Now I am concentrating on GSM downlink FCCH and SCH channel synchronization. Today, the FCCH can be detected roughly. The repo is expected progressing fast recently. BR Jiao Xianjun On Thu, Jan 2, 2014 at 5:37 AM, Sdr Guru &lt;sdrguru1(a)gmail.com&gt; wrote: