Synchronizing 3 USRP-N200

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

On 02 Apr 2013 14:01, Zooz E. 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.