Hi One consideration:
If you do signal injection for calibration, you have the amplitude uncertainties on both the “carrier” and injected signals. The slope at zero on the beat note is likely to be *much* more accurate ( even if gain measurement at audio gets thrown in …) Bob > On Jul 7, 2022, at 5:19 PM, Magnus Danielson via time-nuts > <[email protected]> wrote: > > Hi, > > A well established method is to use a separate offset RF generator that you > can steer frequency to form suitable offset and amplitude to form known > level. You can now inject this ontop of a signal to measure. Consider that > you steer your offset frequency to be +1 kHz of the carrier you measure, and > you set the amplitude to be -57 dB from the carrier. This now becomes > equivalent to having a -60 dBc phase modulation at 1 kHz. > > The RF generator does not have to be ultra-clean in phase noise just > reasonably steerable in frequency and amplitude. > > Cheers, > Magnus > > On 2022-07-07 12:47, Erik Kaashoek via time-nuts wrote: >> Bob, others. >> It has been explained that for the best phase noise level calibration on >> should use a signal with one radian phase modulation and measure the output >> voltage. >> The problem with this approach is the unknown gain of the path into the PC. >> And due to the gain one can not modulate with one radian as this saturates >> the whole path. >> An alternative method for phase noise level calibration could be to create >> an oscillator so bad its phase noise can be measured using a spectrum >> analyzer. To make such a bad oscillator a 10MHz signal was phase modulated >> with noise. The phase noise became visible on the spectrum analyzer just >> above 20 degrees of modulation. The phase noise level saturated between 55 >> and 60 degrees which is consistent with one radian (57 degrees). The >> spectrum analyzer could measure the phase noise at a flat -80dbc/Hz ( yes >> Bob, I better use the right dimensions) >> The simple phase noise analyzer also measured the phase noise at -80dBc >> providing evidence the level calibration was done correctly. >> I also tried to increase the DUT drive into the mixer further above >> saturation so see if this made any change in the measured level but once >> above 0dBm I did not observe any change up to +10dBm drive. Any higher >> levels felt too dangerous. >> There is still a lot of work to be done to further increase accuracy. >> Erik. >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe send an email to [email protected] > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe send an email to [email protected] _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe send an email to [email protected]
