John Miles wrote:
-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. :)
Only if the noise figure of the following amplifier is 4dB or so.
With no extra amplification is used one only needs a signal level of
+1dBm to achieve a phase noise floor of -178dBc/Hz if the output is
extracted through the crystal in such a way that the thermal noise of
the load dominates.
Half of the -174dBm/Hz (at 300K) thermal noise contributes to the phase
noise the other half contributes to amplitude noise.
Thus the contribution of the load thermal noise to the phase noise floor
( dBc/Hz) is -177 + Pout (dBM).
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
neighborhood.
-- john, KE5FX
Bruce
-----Original Message-----
From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@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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