[time-nuts] Phase noise principle and measuring confusion

[Perry Sandeen]

Learned Gentleman,
I've read several articles on phase noise but I'm lost.
I need a *Ding-Dong* school explanation of what it is, why it's important and how one goes about measuring it.
<snip> Bob wrote:
Phase measurement of my GPSDO

Thequick way to do this is with a single mixer. Take something like anold 10811 and use the coarse tune to set it high in frequency by 5 to10 Hz.




Thenfeed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio tone.That tone is the *difference* between the 10811 and your device undertest. 




Ifthe DUT moves 1 Hz, the audio tone changes by 1 Hz.




Ifyou measured the 10 MHz on the DUT, that 1 Hz would be a very smallshift ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have ‘amplified’ the change in frequency by the ratio of 10 MHz to 10 Hz ( so amillion X increase ).



*IF*you could tack that on to the ADEV plot of your 5335 ( no, it’s notthat simple) your 7x10^-10 at 1 second would become more 7x10^-16 at1 second.


OK, this seems to me that this is measuring frequency difference.

wrote:




Thereason its not quite that simple is that the input circuit on thecounter really does not handle a 10 Hz audio tone as well as ithandles a 10 MHz RF signal. Instead of getting 9 digits a second, youprobably will get three *good* digits a second and another 6 digitsof noise.

OK, then would using a 3336A synthesizer work by using the *good* 10811 or other 10 MHz as an external reference and provide, say, a 10 MHz + 100 Hz or 10 MHz + 1KHz work with the 5335? (I have two). Or am I missing something (or a lot)?
Regards,
Perrier