Marcus, They are EndRun Meridian and Meridian II units.
I am very ignorant on this topic. Is it a standard that the 1 PPS should coincide with the top of a 10 MHz cycle? I just wouldn't expect the front end transmit delay, relative to the 1 PPS input, to depend on the 10 MHz reference phase. I don't understand how the 10 MHz reference and 1 PPS input are used to synthesize time. Is the 1 PPS detection done at the master lock rate (200 MHz) or at 10 MHz? On Tue, Jun 23, 2020 at 1:06 PM Marcus D. Leech via USRP-users < usrp-users@lists.ettus.com> wrote: > On 06/23/2020 02:45 PM, Aaron Smith via USRP-users wrote: > > Hello, > > > > I am attempting to release a transmission from an X310 every second. > > To accomplish this, I must measure, and calibrate the delay in the RF > > front end of the radio for my chosen sample rate. I'd like the > > transmission to be released within 1 clock cycle of the rising edge of > > the PPS. > > > > I am feeding the X310 an external 10 MHz reference and 1 PPS, which > > are produced by the same source, and are being supplied to the radio > > with matched cable lengths. The source is a GPS receiver and in my lab > > I have 2 different generations of the GPS receiver. > > > > While calibrating the front end transmit delay I noticed a discrepancy > > in the radio timing between the separate GPS receiver generations. The > > 1st generation of GPS receiver is 50 ns different than the calibration > > for the 2nd generation. When I look at the 1 PPS and 10 MHz output on > > a scope, I noticed that in the 1st generation the PPS occurs at the > > top of a 10 MHz cycle, and in the 2nd generation it occurs at the > > bottom of a 10 MHz cycle. Half a cycle at 10 MHz is 50 ns. I suspect > > this is not coincidence because I have now tested 6 different GPS > > receivers, 3 of gen 1 and 3 of gen 2, and all 3 gen 1 calibrations are > > the same and they are 50 ns different from the gen 2 calibrations. > > > > Is this the expected behavior? Or is there a bug in the X310 code that > > handles timing? I have never worked on hardware, but I would not > > expect the initial phase of a 10 MHz reference to impact absolute time. > > > > Thanks for your help! > > > > > These are external GPS receivers? What kind? Given your scope > measurements, how would this be related to a bug in X310? I'm confused > as to how you're linking the 10MHz/1PPS phasing on your external GPS > receivers to the X310 having bugs. > > > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >
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