Hi Erik,
On 7/8/22 17:12, Erik Kaashoek via time-nuts wrote:
Not something I want to implement on short notice but maybe for the
future.
The biggest limitation in this DIY PNA is the phase noise of the
reference OCXO and the noise of the opamp amplifying the output of the
mixer.
So I was wondering if it would make sense to do the following
1: Split the output of the DUT into two completely separate PNA's
2: Feed the output of the two PNA's into the PC left/right audio
inputs where the noise of both ADC's gets added.
3: Do a cross correlation of the two inputs.
This should (as far as I have understood the feedback) eliminate both
the phase noise of the two independent OCXO's used as reference and
eliminate the noise of the opamps in the two PNA's and the ADC's,
given enough time to do the correlation.
This makes perfect sense. You will not remove the noise of the two
channels, but you will get a direct benefit and as you average the
complex output of successive FFT-cross-correlations you will suppress
the measurement noise even further.
Have you attempted doing a PI-loop as I've suggested?
However, you benefit greatly at optimizing the performance of a single
channel first before going to the cross-correlation. Bob's many good
suggestions should provide you directions enough. Cross-correlation is
not a replacement for doing the homework well, it's to get the icing on
the cake.
Cheers,
Magnus
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