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
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