Hi all,

I am trying to measure phases of the five sinusoids in a loopback configuration with LimdSDR mini in GNU Radio environment.

The flowgraph is described below.

I set the FFT size as 2048, and the five carriers are spaced with integer multiples of FFT bin spacing, thus resulting the period of the combined signal as 128 samples.

I monitor the phase of the FFT bin at the carrier frequency to extract the phase of the carrier.

This perfectly gives the phases of five carriers in a simulation.

However, when I utilize the LimeSuite Sink blocks, there are unpredictable RX timing jumps over time, which screws the carrier phases except the DC carrier.

Please see the captured measurement screen below.

The upper scope shows the received waveform, the middle one shows the phase of the 4th carrier (FFT bin near 6.4 us indicates the phase), and the lower one shows the magnitude of the signal FFT.

Does anyone have good idea for solving this problem?

I want the phase to be static during the measurement.

Regards,

hanc