AD9361 BPSK receive error


We are using zc702 with fmcomms4 and currently trying to transmit and receive a BPSK modulated signal either using MATLAB or Oscilloscope.

The signal is created as follows:

>> b = 2*randi([0 1], 32768, 1) - 1;
>> y = [zeros(1000,1); 0.8*complex(b,b)];

saved to a .mat file and transmitted using iio-oscilloscope. On a standalone RF spectrum analyzer/oscilloscope we observe that the output power is constant.

However, when we receive this signal iio-oscilloscope the I component of the signal is changing it's amplitude over time, sometimes having visible "jumps", as presented on the screenshot. Note that the amplitude starts to slowly decrease after the jump.

When generating a QPSK signal in the same way, everything is fine. RX gain mode is set to 'manual'. What could be the cause?

Thank you in advance.