Re: [Discuss-gnuradio] Synchronizing 3 USRP-N200

[mleech]

On 02 Apr 2013 14:01, Zooz Engineer wrote:

Dear All,

I am having an issue with my 3 USRP-N200 synch.  I use external synch sources for Ref/PPS. The LED's for Ref signal are green and the PPS test is successful for the three boards. However, when I input a sinusoidal signal split and fed into the RF input of the three board and I use a UHD source block for the three boards setting the time and clock as "external", the signals appear still unsynchronized as show in the attached image.

Any insights on this? Is there anything I need to check?

Best regards,
Zo

Two (or more) issues to consider:

 

    o The scope sink has, in the past, had issues with displaying signals that are phase aligned, and showing them not aligned

    o Frac-N synthesizers, as one would find on your daughtercard, won't all have zero relative phase offset when they're tuned.

    o Your splitter isn't necessarily perfectly coherent across all ports

    o Relative phase will drift with temperature due to temperature effects on your cabling and your splitter

If you use SBX daughtercards, you can use the timed-command feature to allow for phase-aligned frequency setting, using a special feature of the synthesizer chip.  Not sure how you get at that from a .grc flow-graph, however.