for one section of my project, i need to know the phase difference between two signal. they are both 40MHz, but out of phase by a certain angle. i have a AD8333 board from Analog Devices, it is a dual I/Q demodulator consist of double-balanced gilbert cell mixers. The board has 2 RF inputs, a LO input, and 4 output (I1, I2, Q1, Q2). I have an oscilloscope to display the results. according to wikipedia http://en.wikipedia.org/wiki/Phase_detector#Analog_phase_detector there is a way to measure the phase difference using IQ demoludator. in this post, https://www.physicsforums.com/showthread.php?t=336619 f95toli mentioned that: the magnitude is just given by the norm (sqrt(I^2+Q^2)) and the phase by the phase angle (arctan I/Q) So is this method bellow correct? to get the phase difference of both my RF signal, i put one the signal into RF input1, and the second signal into the LO, then i display both the I1, and Q1 in the oscilloscope, and get an get the peak to peak magniture for both the I1 and Q1, then calculate arctan I1/Q1, to get the phase difference?