[time-nuts] 74AC gates phase noise

John Miles jmiles at pop.net
Thu Feb 25 22:50:48 UTC 2010

-178 is about the same broadband floor that you see from the higher-end
Wenzel ULN parts.  These can be custom-ordered in the $2000-$2500 range in
single quantities.  Pascall's product line seems relatively similar.
Obviously the carrier needs to be over +4 dBm to get to -178 dBc/Hz at 25C,
but it can certainly be done. :)

What you get for $10,000 and up are the BVAs and similar ultrastable OCXOs.
These have unremarkable phase noise but ungodly stability, around 10x better
than the best 10811s and E1938As.

The most economical way to get into the -170 dBc/Hz range with commercial
oscillators seems to be the Valpey-Fisher parts.  These are in the $100

-- john, KE5FX

> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
> Behalf Of Rick Karlquist
> Sent: Thursday, February 25, 2010 1:34 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] 74AC gates phase noise
> Martyn Smith wrote:
> > Garry,
> >
> > Are you also saying your 100 MHz OXCO is making -178 dBc/Hz?
> >
> > Unless your 100 MHz OXCO is some special $10k type, there's no way your
> > OXCO
> > has a -178 dBc/Hz floor noise?
> >
> > Regards
> >
> > Martyn
> Can you explain this further?
> It isn't clear to me that there is any fundamental reason
> why this noise floor is not possible, especially if other
> specs (like aging) can be relaxed.  Also, the noise floor
> tends to be limited by issues having to do with physics,
> not economics.  How would having $10,000 to spend get
> around the physics issues?
> I think I could approach this noise floor by taking a 10811
> and bringing the signal directly out of the grounded base
> buffer, and then readjusting the ALC to double or triple
> the crystal current.  The biggest unknown is at what point
> the crystal sustains damage.  The 10811 is definitely not
> optimized for phase noise floor.  The designers were well
> aware of this.  But phase noise floor isn't everything.
> Rick Karlquist N6RK
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