Receive amplitude consistency

[Mike]

Hello,

I'm hoping someone can shed some light on an apparent inconsistency
issue I'm seeing with received I/Q amplitude.

I have a B200 directly connected to an arbitrary waveform generator
through an attenuator.  The generator is programmed to repeatedly send a
fixed sequence of AM pulses at a set power level.  On the host (Ubuntu
20.04, UHD 3.15.0), a C++ program simply gathers samples (48 MSPS, sc8
OTW and CPU) and computes the average amplitude as I^2 + Q^2.

During a run of the host software, the reported amplitudes are
consistent from sequence to sequence.

However, if the host software is stopped and immediately restarted,
without changing the generator, the reported amplitudes are again
consistent but at a different level than the previous invocation.

Is there some internal adjustment or variable setting performed during
USRP creation and setup that would cause the received I/Q sample
amplitudes to vary with each startup?


Thanks!