calculating phase difference of two signal from signal generator

[baharehbb]

I used two sinusoidal signals from signal generator. I want to calculate the phase difference between them. I apply the "fft" and the "complex to Arg" block in GNURadio.  the center frequency is 600 MHz and the sample rate is 8MHz. 
but when I run the flowgraph a window is opened for just 1sec and then it is closed and nothing else happens! I would be thankful if you tell me if there is somthing wrong. 

Thank you

[mikeporter]

If the signals that you are wanting to know the phase difference between are sinewaves, it would seem to me that the phase difference is simply the delay between zero-crossing points or some other reference point.

Next, you are mention a flowgraph. Do you mean your program? What window is opened, and what does it say?

Mike...

[baharehbb]

I fixed that problem Mike. 

Thank you

the problem was that I had put 2 uhd sources block in my program instead of one source and two channels. 🙂 and also my signals are sinusoid. 

but now another problem is that the phase difference that is calculated is changing. I mean once it says 2.2 radian (which is correct since my inputs have 180 degree phase difference) and a few seconds later it changed to another number like 0.3 !!! and other numbers.

Thank you again for your help

[johnsold]

Please post your VI with some typical data saved as default (we do not have your hardware). It is very difficult to debug a paragraph.

Lynn

[mikeporter]

If you plot the two waveforms as they are acquired, are they indeed 180 degrees apart? and not changing?

Mike...