[USRP-users] Frequency offset between two USRPs B210 synchronized with use of Octoclock-G

Marcus D. Leech mleech at ripnet.com
Fri Oct 6 17:17:46 EDT 2017

On 10/06/2017 03:33 PM, Piotr Krysik via USRP-users wrote:
> Hello everyone,
> I synchronized two USRPs B210 with use of Octoclock-G and the attached
> gnuradio-companion flowgraph.
> I've connected signal generator generating sinusoid to both devices (it
> was on frequency 694.5MHz while USRPs were tuned to 694.3MHz, signal
> power was about -40dBm). What I would expect is to see constant phase
> offset between signals received by both USRPs (perhaps changing slightly
> with temperature etc.). However what I see is constant changes of phase
> that corresponds to frequency offset between two devices. Moreover this
> frequency offset changes significantly from one execution of a flowgraph
> to another (look at the image):
> relative phase of two B210's
> What is on this image is not normal - i.e. much better phase offsets I
> can get on two synced RTL-SDR dongles, working under patched driver.
> Questions:
> 1. Have anyone synchronized USRPs B210 up to having constant phase
> offset between the devices?
> 2. If yes - how?
> Best Regards,
> Piotr Krysik
One thing to note is that UHD *DOES NOT* do timestamp alignment across 
multiple UHD container objects, so you can expect there to be a random 
phase-offset between the two halves in this scenario every time you run.

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