[time-nuts] Re: Best frequency to start for GHz synth ?

[Bob kb8tq]

Hi

If you were going insane on a fountain, you likely would go with one of the 
sapphire whispering gallery devices as the start of your chain. A good one
will blow a quartz crystal based part away ….

Past that, lower is better for crystals and “Time Nut” parameters. Q will be higher
at lower frequencies. Physics is the source of that, so no change in process will
“help” you. 

Package size limits just how low you can go with a low-loss design. If at some 
future date a bigger package got tooled up ( think government funding ….) those
limits might change. In this case “tooled up” involves tooling a lot more than just
the can and base …..

So, yes, you still are “stuck” with 5 MHz ( or something close to that) for really
good ADEV and close in phase noise. 

The other thing that might happen some day is the same sort of money being spent
to get another piezo material up and running. There are some that might give you
higher Q. So far all the attempts I’ve heard of have hit walls in various areas. Best
guess is that it goes back to learning how to “grow” high stability bars for some of
these odd materials…..

Unless something really strange happens, the odds of somebody putting big 
money into any of this is in the “very remote” category. The people who are crazy
needy already have the sapphire stuff. 

Bob

> On Mar 31, 2021, at 12:44 PM, Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:
> 
> Somewhat related to the discussion about GPSDO's I have a basic question:
> 
> It used to be that 5MHz was the "hot spot" for crystals on the parameters we care about as time-nuts.
> 
> Have advances in X-tal science changed that ?
> 
> To make it a concrete question:
> 
> If tasked with designing a Cs/Rb beam/fountain/whatever today, would one still start the synthesizer-chain at 5 MHz or would a higher frequency give better results ?
> 
> -- 
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> phk at FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe    
> Never attribute to malice what can adequately be explained by incompetence.
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com -- To unsubscribe send an email to time-nuts-leave at lists.febo.com
> To unsubscribe, go to and follow the instructions there.