Retrieving phase

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kzt
Posts: 1
Joined: Sat Aug 11, 2018 7:05 am

Retrieving phase

Post by kzt » Sat Aug 11, 2018 8:03 am

Hi,

I have been trying to do VNA-ish operation with libbladeRF and C code. So far, I could synchronise tx and rx with timestamp and obtained magnitude looks ok. However, I cannot retrieve phase.

What I do at a frequency is: referring to some earlier posts, tx and rx frequencies are set at a few MHz apart. Sampled waveform is Fourier transformed and a complex number is extracted at the frequency bin, which is calculated from the frequency offset of tx and rx.

I found that the phase of sampled waveform that oscillating at the beat frequency is different each time as shown in below.
rx_signals1.jpg
This is what I can get with 1 MHz beat frequency, 20 MHz sampling rate, and repeated 70 times. I expected all the lines to be overlapped.

Also there is a break later in the sampled waveform where phase also changes, although I made tx waveform for full 16384 samples long, as
rx_signals2.jpg

Would be really helpful and appreciated if some could help me out on this.

Thanks

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