Hello,


I'm using a series of x310 USRPs synchronized together using both an external 
10 MHz reference and a PPS. I have two configurations: in my lab an Octoclock 
provides the PPS signal, and in the field configuration I use a GPS referenced 
stratum 1 NTP 
server<https://www.microsemi.com/product-directory/gps-instruments/4135-syncserver-s650>.



The lab configuration USRPs blink an LED on the front panel in time with the 
PPS. The field configuration does not blink the LEDs at all. Both 
configurations light the 10 MHz reference LED.



I am not fully sure if this is a problem. Occasionally when I run the 
application in the field configuration, it works for about a minute and then 
appears to drift out of sync, however most of the time everything seems to 
operate as intended. It's very possible my field configuration has other 
issues, and my system has not quite reached the maturity to be running multiple 
hour/day long test to measure drift on the application synchronization.



I examined the PPS connection with a T cable and a scope. Both produce a PPS 
pulse with a sharp spike to an initial voltage, followed by a longer 
exponential curve up to 5V. The octoclock drives to 2.5V initially, and the 
syncserver drives to 4V initial.



I have tried using shorter cables and a 6dB attenuator on the syncserver 
connection to see if I could get the PPS to light, but neither seemed to have 
any effect.



Does anybody have any guidance on how to make sure my x310s in the field 
configuration are actually benefitting from the PPS?



Thank you!

Richard

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