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

[Marcus D. Leech]

On 11/01/12 06:56 PM, Armando Rocha wrote:
> 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).
>
>
The NCO reprogramming isn't, as far as I know, phase-continuous.  Josh
and/or Jason could likely comment,
 but my understanding is that phase is only left unperturbed when you
leave the frequency intact.

-- 
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org