[time-nuts] Thunderbolt versus Home made
SAIDJACK at aol.com
SAIDJACK at aol.com
Thu Mar 1 13:46:06 UTC 2007
In a message dated 2/27/2007 15:01:44 Pacific Standard Time,
not.again at btinternet.com writes:
Sorry, my original post was not very clear - I had only wondered if
faster PPS signals might ever help with the measurement each second; I
didn't mean to suggest that they might affect the required overall
loop time much. ( Thinking back to all the posts a couple of months
ago, I should probably resist any urge to comment on the effect of
sawteeth on stability for the moment... )
Anyway, I was just curious. It's one of the many things I don't have
much time to mess with, so wondered if anyone else had - but
apparently not.
Angus.
Hi Angus,
in a traditional PLL where the low-noise reference source is basically
"disciplining" a noise oscillator (VCO in this context), the phase comparator
frequency is related to the achievable phase noise. Higher comparison frequencies
result in lower phase noise.
Take a look at National Semiconductor's application notes about this, they
give you the underlying math. Analog Devices has great app notes, a PLL
simulator etc on their website as well.
For a GPSDO, the tables are exactly turned: the reference is much more noisy
(short term ADEV) and the VCO is the provider of low short-term phase noise,
while the GPS reference provides low long-term phase noise.
bye,
Said
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