Hello!
Can you describe what you are attaching to the oscilloscope? The output of the GPSDO is a 10 MHz waveform. This should be aligned between the GPSDO's. The derrived local oscillators from the two devices will not be phase algined.
Phase Alignment vs. Phase Coherence
Sharing the common 10-MHz reference among USRPs allows a phase-coherent Local Oscillator (LO) to be synthesized using a fractional-N frequency approach. During synthesis, as the reference is divided, the phase may lock on either rising or falling edges producing a constant but arbitrary phase offset on each channel. In MIMO communications, these fixed yet arbitrary phase offsets are corrected by the same algorithms that perform multipath estimation and correction.
Beam forming applications however require phase alignment of the LO, so that phase can be controlled or captured through baseband I and Q. Clever methods have been used to detect the phase offset in the USRP using a know reference signal and then apply the correction to the received signals for receive direction finding and beam forming research.
