[time-nuts] Designing and building an OCXO and GPSDO

[Bruce Griffiths]

Luis Cupido wrote:
> Bruce, tks for your reply.
>
>  > The latest spectrum analyser offerings from Agilent have similar phase
>  > noise floors for both the millimeter wave and low frequency spectrum
>  > analysers.
>
> Yes, but kind of puzzles me a bit since I would
> be expecting phase noises more than 10x worst on a
> SA covering DC to 1GHz (+/-)
> (since the LO for this is an YIG oscillator circa 3GHz locked to a 
> reference)
> comparing with an FFT analyzer that uses a few tens MHz sample rate.
>
> Assuming similar 10MHz reference oscillator the SA
> gets it multiplied by 300 while a low freq SA (preferably FFT)
> gets it multiplied by 10 maximum.
> How can they claim similar performance ?!
> ---
>
> Ok on the rest, tks.
>
>
> Luis Cupido.
>
>
>   
Luis

Perhaps the local oscillator isn't the limiting factor for the low 
frequency analysers.
The claimed noise floor is in the vicinity (within 10dB) of -120dBc/Hz 
for the analysers for which I checked the specs.

If the 10MHz reference has a phase noise floor of around -160dBc/Hz
this is only degraded by 50dB or so to -110dBc/Hz when multiplied by 300.
The YIG oscillator phase noise floor may perhaps be a little better than 
this.

However, since state of the art ADCs have a phase noise floor of around 
-150dBc/Hz one would expect a lower phase noise floor from the lower 
frequency spectrum analysers.
Surely there's an FFT based spectrum analyser out there wit this level 
of performance.


Bruce