[Discuss-gnuradio] Phase measurement with Ettus Research N210

[Daniele Nicolodi]

Hello,

I'm using an Ettus Research N210 with a LFRX daughter-board to do data
measure the phase of a signals referred to a 10 MHz clock.

To start I want to characterize the phase noise of the device, therefore
I send to both the RX channel and to the frequency reference input the
same 10 MHz signal. I configured the N210 for 200 kHz sampling and a
carrier frequency of 10 MHz.

When I look at the data I obtain, I see a constant phase drift
corresponding to a 9.32 mHz frequency different between the signal I
send to the RX channel and the frequency at which the N210 does the
demodulation.

Given that the signal and the clock are derived from the same oscillator
(in this simple case are the exact same signal), where does this
difference come from? How can I get rid of it?

I imagine it comes from the fact that the ADC sampling frequency is not
an exact multiple of the signal frequency, but I haven't found details
on how the ADC sampling frequency is generated, thus I have no idea
about how to make it an exact multiple of the signal frequency.

Thanks. Cheers,
Daniele