AM demodulation and carrier phase measurement of multiple signals simultaneously

Hello All,
I need to extract and compare the carrier phases from a number of
medium wave AM signals using a 5600 downconverter and a 5122e
digitizer. The signals are all real off air broadcasts, and so are in
the band 500kHz to 1500kHz. Since the transmitter frequency references
may all drift I guess the most sensible way to do this is to filter and
mix each signal down to the same IF and track their relative phases.
However I'm not sure what clever tricks can be done with current
Labview vis. I've had a dig through what I have (I have the modulation
toolkit amongst others) but can't use the features based around the
5660 due to my hardware. I can see the signals where they should be on
a spectral plot, but have not had much luck getting sensible looking
results using mt_niscope_demodulate_am.vi. I am currently tuning the
5600 to 15MHz rather than attempting to tune it to central frequencies
around 1MHz, I presmue this is the right thing to do? Could someone
point me in the direction of some good starting point? Any suggestions
welcome
Thanks
Ramsey

Hello Ramsey,
I assume you are trying to capture these AM signals and compare their relative phases all against each other. Sort of like saying the AM 1300 carrier is X degress in phase different from the AM 1530 carrier.
This is what I would do. I would use the full PXI-5661 RF analyzer and capture the entire AM band in the acquisition. This is roughly a 1 MHz bandwidth. At this low bandwidth, a low IQ sample rate can be used with the PXI-5661 (1.25 MSamples/sec gives the PXI-5661 a 1 MHz IQ data BW). With this low IQ rate, you could actually stream the entire AM band to hard drive for some time.
Since you have recorded the AM band to disk for a period of time, you can extract all the relative phase information you want. And the receiver reference is the same for all acquired data so the only variation will be due to the Tx side.
Look at this example:
RFSA Acquire Continuous IQ.vi
located at:
C:\...\<LabVIEW>\examples\instr\niRFSA
Regards,
Andy Hinde
National Instruments

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Average Collected Data.vi ‏13 KB

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AM demodulation and carrier phase measurement of multiple signals simultaneously

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