Hi Tarik,
that REF out port is the 10 MHz clock, and you can choose the internal
GPSDO as clock source[1]. Same goes for the PPS out port.
Theoretically, you could "daisy-chain" your USRPs, but I wouldn't
generally recommend that (we haven't characterized delay, and also, if
you can, always avoid adding phase noise multiple times). Instead, what
about this:
Use your GPSDO-equipped USRP to output both REF (10 MHz) and PPS out
(PPS), and use an external clock distributor (that could be something
as simple a bunch of logic buffers, if you have some 74xx cmos lying
around, or something off-the shelf, or something using a dedicated
clock distribution IC – there's plenty to choose from, [2]) to generate
as many 10 MHz signals as you need. Same goes for PPS; note that PPS is
evaluated on a clocked basis, so you don't need crazy rise times in
your buffer – instead, make sure your 10 MHz is nice and periodic).
If you'd be aiming for an off-the-shelf solution: you might consider
buying an Ettus Octoclock – eight 10 MHz and eight PPS outputs, all fed
from the same clock source. And: you can actually go ahead, and
(carefully! These pins are mechanically delicate!) remove the GSPDO
from your X310 and use it in the Octoclock – to make it an Octoclock-G.
Alternatively, you can feed the Octoclock with whatever clock source
you want to use (for example, if you're using a spectrum analyzer to
...analyze the spectrum, then you might want to rather use that SA's 10
MHz output instead of GPS, even if it's "worse": that way, you'd at
least be frequency synchronous to your measurement device).
Best regards,
Marcus
[1] https://files.ettus.com/manual/page_usrp_x3x0.html#x3x0_hw_rear_pan
el
[2] haven't tried this, so please evaluate if appropriate for your use
case: http://www.ti.com/tool/cdclvc1310-evm
On Wed, 2018-02-14 at 17:56 +, Tarik Kazaz via USRP-users wrote:
> Hello everyone,
>
> I am considering to synchronize several USRPs Xseries. However, I
> have only one device with integrated
> GPS disciplined oscillator.
>
> I am wondering whether it is possible to use the device with GPS
> disciplined oscillator as a master clock source?
>
> What is the output of REF Out port on USRP Xseries devices (is it
> 10MHz or PPS signal generated by GPSDO or some
> other configurable signal generated from fpga)?
>
> Kind Regards,
>
> Tarik
>
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