[USRP-users] Why does the external 10MHz clock only works if I disconnect the 1-PPS signal?

Michel Chauvin M.Chauvin-contractor at cablelabs.com
Mon Oct 9 19:07:41 EDT 2017


I've been trying to use an external clock with the USRP B210 board. We have a time server which is locked to a GPS signal which provides both a 10MHz output and 1-PPS output. 

When I connect both 10MHz and 1-PPS output and use the external clock source the USRP B210 and OAI eNodeB have issues. (I get a large number of uplink re-transmissions between a Huawei B593 UE and a OAI eNodeB and a large number of these re-transmissions fail to decode completely which eventually leads to the UE being disconnected).

Interestingly, if I disconnect the 1-PPS signal from the USRP B210 and only leave the 10MHz clock from the time server connected to the USRP B210, the USRP B210 works perfectly!

I understand the 1-PPS signal is for time stamp alignment.

Q1: Do I need to use the 1-PPS signal or can we leave it disconnected? 
Q2: If yes in Q1, what benefit do we lose, if any, if we disconnect the 1-PPS signal from the USRP B210? Is it needed/used in when the USRP B210 is used with an OAI eNodeB?


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