Forums › SA Series Discussions › SA124B Minimum phase noise
- This topic has 2 replies, 2 voices, and was last updated 6 years, 4 months ago by
hendorog.
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hendorogParticipantHi,
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.
Justin CrooksModeratorUsing 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.
hendorogParticipantThanks for the insights, much appreciated.
I grabbed the old API, and will have a play with it – minor issue was the Legacy API manual is linked to the Headless API manual on the SH.com website. The SH.eu website had a copy though.
SM200A – one day 🙂
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