Hi Jim, thanks. I obtained the cal certificate for the other E5052A today. It was calibrated less than a year ago and this one shows an even lower noise floor.? It's a slightly newer unit and it has some hardware changes although I'm not sure if these changes are the reason it is slightly cleaner than my E5052A. The service manual shows the hardware changes wrt serial number. It also has the same internal spurious frequencies as mine and they appear to be a bit higher in level. It has the backlight spurious at 60 kHz as well.
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Looking in the service manual, it appears to describe this test at 70 MHz where a (low phase noise) PSG sig gen is used as the signal source at 70 MHz and it is passed through a 10 kHz wide BPF. Presumably some form of crystal filter? This will then shave off all noise down to the thermal level in the stopbands of the filter.
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I tried this with my E5052A using a lower test frequency (10.7 MHz) and a 15 kHz wide crystal filter and I saw about -175 dBc/Hz at offsets above 1 MHz. Not as good as the newer E5052A but the cal certificate did quote an uncertainty of about +/- 4dB for this test type. I really should do the test at 70 MHz as well. The noise floor may be degraded for carrier frequencies as low as 10.7 MHz.
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