Hi, I'm trying to use a common reference signal to sync two USRP-2901s. I'm using gnuradio with the default USRP sink and source blocks, and we're using an external signal generator into the "REF IN" port.
If we use the same USRP for the transmitter and receiver (but on different subdevs (RF channels)), when the reference signal is not present, we see an error as expected: "usrp_sink :warning: Sensor 'ref_locked' failed to lock within timeout on motherboard 0." Turning on the reference signal generator gets rid of this error. However, when we try to use two USRPs connected to the same reference signal, the error does not appear even if the signal is off. Setting one radio's clock source to be "internal" and the other's "external", and then modifying the reference signal frequency seems to have no effect, so I think the radios are not really synced. I would expect that I'd see a frequency difference if the reference signal frequency was slightly incorrect in a loopback scenario. Is there a reason why the error does not appear when using multiple USRPs even though there is no reference signal, and the radios remain seemingly unsynchronized? Thanks, Eshan Ramesh
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