[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)

[Magnus Danielson]

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 -- time-nuts at lists.febo.com
> To unsubscribe send an email to time-nuts-leave at lists.febo.com