To provide more details: - The two USRP devices each have their own GPSDOs.
- I have separate TX and RX programs. Each one synchronizes to their GPSDO and then synchronizes phase by creating streamers with a time_spec with a specified gps_second in the future, following the instructions in the manual. The issue is: I am seeing a random phase offset in the received data each time I run my programs. I don't see a phase offset if I specify a zero Hz center frequency, so there might be a clue there. For my application I need to specify a non-zero center frequency. I'm just trying to find out whether this result is expected with the HW and/or SW setup that I have, or whether it is a bug in my current version of UHD, or I am doing something wrong? Has anyone ever tried to synchronize two USRPs each with their own GPSDO using non-zero center frequencies? Someone mentioned off-list that there was a bug in earlier versions of UHD that caused the CORDIC not to get reset but that has been fixed in newer versions. I'm running UHD 3.15.0. Someone else asked off-list whether I am using the same or separate GPSDOs. The answer was separate GPSDOs, but does that make a difference? Thanks, -ben From: USRP-users <usrp-users-boun...@lists.ettus.com> On Behalf Of Lapointe, Benjamin - 0333 - MITLL via USRP-users Sent: Thursday, September 12, 2019 4:25 PM To: usrp-users@lists.ettus.com Subject: [USRP-users] random phase offset when trying to synchronize two USRP N210s Hi, I am trying to synchronize two USRP N210 devices, one for TX and one for RX. I've followed all of the instructions in the "Synchronizing the Device Time" and "Align CORDICs in the DSP" seconds of the manual (https://files.ettus.com/manual/page_sync.html); however, I'm still not getting complete success. I can synchronize the two devices only if I use a center frequency of 0 Hz, as shown in the attached cf_0e6.jpg. If I use a center frequency of 10e6 Hz for both TX and RX then there is a phase change between program runs, as shown in the attached cf_10e6.jpg. Each screenshot shows five recordings spaced 20 seconds apart for two runs of the program. Should these results be expected? - If so, can someone explain why there is a random phase offset when using a non-zero center frequency. - If not, what am I doing wrong? I can share my code if that helps. I also tried following the instructions in the "Align Los in the front-end (SBX, UBX)", but that didn't help. I didn't think it would help since I'm using LFTX and LFRX boards. My hardware setup: Transmitter: N210 with a LFTX and GPSDO Receiver: N210 with a LFRX and GPSDO Any help/feedback would be greatly appreciated, Thanks! -Ben
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