[time-nuts] Some More questions

[Neon John]

On Wed, 18 Jan 2006 21:59:12 -0600, Didier Juges <didier at cox.net>
wrote:

>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 
>factor..

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
---
John De Armond
See my website for my current email address
http://www.johngsbbq.com
Cleveland, Occupied TN
A foolish consistency is the hobgoblin of little minds.-Ralph Waldo Emerson