measuring Phase matching between channel

biff44 said:

I once used a tektronix MSO4104 scope to measure a phase differencing microwave system prototype. I used the multichannel inputs and downconverted (sharing one LO generator) each microwave channel to lower frequency to two of the inputs. I used the labview software that came with the scope to capture the two IF waveforms, and used a simple FFT process to figure out the phase angle. It worked very well, and was pretty accurate (much better than 1 degree) for phase.

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BradtheRad said:

Are you talking about stereo radio broadcasts? The left and right channel are combined and transmitted simultaneously.

The place where phase differences might occur is after the stereo detection stage, in unmatched lengths of wiring, or capacitive delay, etc.

If you want to observe phase differences with an oscilloscope, use the X-Y method. One signal for vertical, one signal for horizontal. Two matching signals, in phase, create a single diagonal line with the high end at top right onscreen.

This method also makes mismatched signals stand out.

You can tell when a broadcast is stereo if the image looks like rapidly changing drawings of chaotic steel wool pads.

Furthermore if the channels are not in phase, the diagonal line (or chaotic steel wool pads) will have its high end at upper left onscreen.

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