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Hi,
I have managed to acquire a very low noise signal generator (Marconi 2041). I have been using that with a mixer as a downconverter, so I can make phase noise measurements using my SA124B. I have connected the 2041 and the DUT to a mixer, and the IF output of the mixer to my SA124B.I can choose the IF measurement frequency from DC – 600MHz or so, and I would like to choose a frequency which minimises the PN contribution of the SA124B to the measurement.
As I understand it, there will be a contribution from the SA124B first LO, and one from the LO in AD9864 when it isn’t in hung mixer mode.
So I was wondering firstly – this is a long shot – if there is any low RF frequency I can choose which will use direct sampling by the ADC and bypasses both of the LO’s?
Secondly if there is a way of forcing the AD9864 into hung mixer mode which I think should avoiding the PN contribution from the second LO in the AD9864? Any other ideas – sadly I can’t affort an SM200A!So far I have a PN floor of about -120dBc/Hz @ 10kHz offset using 5MHz as the IF.
Using our legacy API, the device can be configured to use the 2.9 MHz IF (hung mixer mode). You would have to use a higher frequency than 5 MHz (something like 15 MHz at least). I’m not sure it would get you significantly better numbers, but it might give you a few more dB.
There is probably enough RF-to-IF leakage in the mixer that you could use this mode (SHAPI_Configure, use 2.9 MHz IF set to true) and inject your signal directly at 2.92 MHz (at a higher amplitude). This is the closest to direct ADC access the SA series offers.
These are just my thoughts, and may not work, but if you give it a try let me know what you find. The BB60C has more direct ADC access, but realistically, the SM200A would be the ideal choice.
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