Hi,
Given a set of synced
(i.e., using external GPS REF/PPS), time-commanded and calibrated
(i.e., through compensating for the phase/mag offset between digital Tx chirp prior to transmission and ADC'ed Rx signals) N200 devices with LFTX/LFRX daughterboards, that work with coherent LFMCW chirps, I am still seeing a tiny drift (both in the magnitude and frequency) of the calibrated back-scatter Rx chirp received at time t1 when compared to an Rx chirp received at an earlier time t0.
The more the N200 device runs (e.g., 5 hours), the greater the drift is. Obviously, this drift is pertinent to both the DAC and ADCs and the GPS referenced clocks of the N200 devices.
My questions are:
1- Why I still see such drift although my devices are synced with an external GPS? and how do I correct for it?
2- Can the PLL Carrier Tracking block in GRC be used to track and correct for such a drift? If so, how do I set the max/min freq inputs for this block?
3- Can AGC2 or AGC3 block be useful in this regard? If so, are there any examples to explain how the input parameters of these blocks can be set up?
Thanks.
Best regards,
Khalid