[time-nuts] Some More questions
didier at cox.net
Wed Jan 18 22:59:12 EST 2006
Tom Van Baak wrote:
>>I should be able to improve the receiver performance some by ovenizing
>>it. I wonder if it would be worth the effort?
>You can check this with a hair dryer. Measure the effect
>of a 10 C rise and then extrapolate back to 0.1 or 0.01C
>to see what the result of making an oven would buy you.
One problem with that approach is that crystals that are not intended
for oven operation are optimized for minimum frequency change over 0-50
or some other "normal" environment temperature range, and at 75 degree C
or wherever you are going to run the oven at, the temperature
sensitivity might be much greater than around 25 degrees. So even though
the oven might reduce the temperature variation by a factor of 10 or
better, the overall frequency sensitivity may not improve by the same
Check the following curve
See the curve that is the most flat in the middle and see how rapidly it
rises at temperatures above 70 degrees.
Then, I am not sure all GPS receivers actually use their internal
crystal oscillator in a PLL as the timebase. I have read that some work
by removing or adding pulses in a discrete fashion rather than phase
locking, and this offers significant jitter, making the 1 PPS only
useable to phase lock a reference oscillator with a very long
integration period to eliminate the jitter.
Now, I can't find the article describing that technique, so it may have
been old news.
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