We are doing a test which consists in sending a waveform from Matlab to the signal generator SMB100A and sending it through a cable to the r&s spectrum analyzer just to have a channel. We set the trigger manually in the signal generator in the restart mode, then we set the frequency and the chip rate in our Matlab code as well as the buffer size and the connections. Finally, we read the waveform, which is already stored in the signal generator , and we set ARB state ON: we are using the arbitrary customized digital modulation. However, the channel impulse response is different every time that we run the test: there is a portion of the signal that looks like an offset; we think the signal is shifted because of an inversion in the phase. Any clue about why this happens?