Q:* As I change the frequency of the RF source, I observe a phase
drift between the master and the slave. Is this OK? A:* This is the expected behaviour, since a WR DDS link behaves like
a cable of fixed length. Therefore, by looking at the master and slave
RF output on the oscilloscope, we see the original RF and its copy
delayed by 200 us. If the RF period divides this delay without a
remainder, the signals appear in phase, but as the RF frequency changes,
so changes the period and there's no more an integer number of RF ticks
in the delay interval. The DDS RT software compensates for the phase
shift between the master and the slave at the startup to enable
short-term phase measurements.
This applies only to the shift between the master and the slave. If
there are multiple slaves in the network, they will be phase-locked to
each other regardless of the momentary RF frequency.