[time-nuts] Some More questions
jgd at johngsbbq.com
Thu Jan 19 14:15:29 EST 2006
On Wed, 18 Jan 2006 21:59:12 -0600, Didier Juges <didier at cox.net>
>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
The approach that I've taken in the past is to "room temperature
ovenize" the oscillator. That is, put it in an insulated enclosure
with a Peltier junction and set up a 4 quadrant PID control loop to
maintain the temperature at, say 80 deg F.
One of the most successful applications was to an inexpensive
frequency counter with a simple TCXO. I applied some RTV to the
crystal and oscillator chip for heat conductivity, laid a small
Peltier junction and a thermistor in the RTV, then enclosed that area
of the board with aerosol spray foam (Great Stuff), along with a
similar amount on the bottom of the board. I set the control point to
80 degrees. After aging for a couple of years, that counter settled
down to be one of my most stable, despite costing less than $200.
I brought out a test point so I could monitor the power to the
Peltier. Even when using the counter in a hot 2-way radio shack, the
temperature remained precisely at 80 deg.
My main curiosity with the GPS is whether there are other
stabilization methods employed that would make ovenizing moot.
John De Armond
See my website for my current email address
Cleveland, Occupied TN
A foolish consistency is the hobgoblin of little minds.-Ralph Waldo Emerson
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