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 +0000, 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 > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com _______________________________________________ USRP-users mailing list USRP-users@lists.ettus.com http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
