Unexpected IQ phase shift in GPSDO Kiwi [workaround in v1.590]
It has been a welcome surprise to find how useful the Kiwi can be for radio research projects when the Kiwi is fed by a GPSDO like the Leo Bodnar products. While the GPS referencing in a standard Kiwi proeuces exceptional frequency accuracy, measuring the doppler shift of WWV and other signals requires the even greater frequency accuracy produced when the Kiwi is fed by an external GPSDO.
In exploring the capabilities of the Kiwi when fed a Bodnar's 66.660000 Mhz external clock (exactly 5555 times the 12000 sample per second audio output wav file), I have sought to verify the frequency accuracy of the Kiwi's signal processing by viewing the IQ display of a 16,665 Mhz RF signal generated from the second output of a dual output Bodnar. That RF is exactly 1/4 the frequency of the 66.66 ADC clock and so I expected to find no long term phase difference on the IQ display.
So it surprises me that that IQ display shows a 360 degree rotation in about 120 seconds. My oscilloscope shows no phase shift between those two Bodnar signals during that 120 seconds, so it seems that something in the Kiwi's signal processing to the IQ display runs off of a different clock than the ADC.
My goal is for kwirecorder to create a stream IQ wav files with no lost IQ samples, so if this IQ display drift is introduced only in the IQ display extension it won't be a problem for my application.
So before I start validating IQ wav files, should I expect the same drift in them that I observe on the IQ display?