[Discuss-gnuradio] Unwanted relative phase change after programming a device

[Armando Rocha]

Dear all

I am using USRP1 with two basic RX daughter boards and two input signals 
(one at each Basic RX) with the same frequency.

The two 10. 7 MHz signals cartesian components:
- (I1, Q1) from one channel of the 1st Basic RX card
- (I2, Q2) from the 2nd Basic Rx card
are mixed with the NCO at about 10.7 MHz to almost DC, decimated and 
sent to PC.

The PC software computes the received signal frequency, amplitudes and 
the relative phase that remains constant along the time if the NCO 
frequency is not changed.

To compensate frequency drifts the NCO is periodically adjusted by 
reprogramming the two devices." using the tune function.

After this reprogramming however the relative phase between the signals 
often (but not always) changes a lot (not always the same phase change).

A detailed suggestion to solve this problem is appreciated as accurate 
phase measurement is important in my application (I can not find a clear 
response to this issue in the discussions).


--
Armando Rocha (Professor)
Universidade de Aveiro, DETI/IT
Campus Universitário Santiago
3810 193 Aveiro