2RX Phase measurement issue -180 degree phase jump

#1

Hi!
I want to use LimeSDR to measure the magnitude and phase of a signal connected to the 2 RX channels of the Lime.
I am using one of the TX channels to generate a sinusoid, the Lime’s TX port is connected to the input of a power splitter. The outputs of the power splitter are connected to the RX channels of the Lime (as shown in the below picture). For the moment I am working in the 35-200 MHZ frequency range.

LimePowersplitediagram1b

The first problem I run into is that the phase of both channels can be (approximately) 180 degree out of phase in a random way. The following screen shoots of the " I versus Q" plots of the Lime suite GUI (FFT viewer) shows the problem very well (All this graphics are taken at the same frequency=100MHZ, just by pressing the Start-Stop button the points in the constellation jumps from one position to the other).

Is there any solution or a workaround for this problem?

Regards
Mauro.

Reading data streams of the 2 RX channels simultaneusly?