On 05/07/2018 11:11 AM, shachar J. brown via USRP-users wrote:
Hi All,
I am trying to measure the phase difference of a received signal between
the two RX ports of the B210. (In the grc I simply ran each of the two
received signals through an FFT, took the bin with highest amplitude and
extracted it's phase, and finaly - subtracted the two).
I experimented with a single signal source generator split in two. I
first connected both RX ports with matching wires and received zero
phase difference as expected.
Though when I added a wire of some length to one of the ports, the
received phase difference was NOT as expected by theory.
(In short, I sent 100[Mhz] pure sine wave, thus wavelength of 3[m] or
shorter, the extra wire was 0.508[cm] long, thus I would expect a phase
diff of about 60 deg or more. Frankly I received a phase diff of about
18 deg).
What am I doing wrong?
I thought maybe the phase calculation of gnuradio is done on the
baseband frequency and not on the RF, and therefore the phase diff would
be different. Is this my problem? (e.g. if the baseband is only 30[Mhz],
then expected phase diff would be 18 deg). If that is the case - how can
I know which baseband frequency the AD9361 has chosen?
GNU Radio works with signals at baseband. It sounds like you might not
have set a RF frequency in the USRP source block. The default is 0, and
I'm not sure what the B210 would tune to in that case.
I don't know whether this experiment actually works, but to do it you
would tune to 99M, set the sample rate to 2M, and see what happens. The
peak should be right in the middle.
Also, make sure your signal generator is sending out a very low signal -
try something like -40dBm. Max is higher, but there's no need.
Thank you all for your time,
Steve
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