[time-nuts] Re: Testing GPSDOs

[Erik Kaashoek]

Andy,
Thanks for these references
Using two 5GHz PLL's, one hard referenced to the in-house standard and 
the other to the TCXO under test and the outputs of the PLL's send into 
a mixer producing a 10kHz output send into a PC for FFT analysis made 
the performance of the TCXO very visible.
Can I assume 1 Hz variation of the audio signal is 2e-10 variation on 
the 10MHz signal?
My concern with the high resolution FFT is the length of the FFT, does 
this not hide fast frequency variations? Or will these variation become 
visible through blurring of the peak and as long as the peak is nice an 
sharp one can assume the signal is stable over the FFT length?
Erik.
On 20-2-2022 18:38, Andy Talbot wrote:
> Dunno if this will do what you want ...
>
> Get hold of some PLL Fract-N synthesizers, like the ubiquitous ADF4351, so
> you can multiply up from two sources. Mix the outputs and look at the
> frequency deviation over time.
> My tests using this technique can be seen at
> http://g4jnt.com/10MHz_Reference_Source_Stability.pdf    and
> http://g4jnt.com/ShortTermStabilityLeoBodnarGPSDO.pdf
>
> I used synths I had to hand, but anything that will multiply up your test
> and reference signals to a pair of frequencies separated by a few kHz, so
> you can look at the beat note using soundcard software.
>
>
> Andy
> www.g4jnt.com
>