[time-nuts] Another "atomic" clock question

Bob Camp lists at rtty.us
Tue Mar 4 17:45:55 EST 2014


Hi

Be careful of what you wish for. 

One way to “eliminate” the hanging bridge is to have the oscillator exactly on frequency. That sounds fine. The problem is that you are always in the middle of a bridge. The other way is to put the oscillator well off frequency. That way you have lots of sawtooth action. There are lots of ways to get an oscillator off frequency ….

Bob

On Mar 4, 2014, at 12:00 PM, Didier Juges <shalimr9 at gmail.com> wrote:

> What would be more interesting would be to adjust the temperature of the GPS receiver's oscillator to eliminate the hanging bridges altogether, kind of like Trimble does with the Thunderbolt, except that they do it directly instead of indirectly. That may require to characterize the crystal oscillator to find out if it has an appropriate control range over temperature.
> 
> Didier KO4BB
> 
> 
> On March 3, 2014 6:51:54 PM CST, Charles Steinmetz <csteinmetz at yandex.com> wrote:
>> Chris wrote:
>> 
>>> If do have an external frequency reference then the crystal itself 
>>> makes a good thermometer.  So why not use THAT thermometer to 
>>> control the heat added by the resister.  Such a system would respond 
>>> to changes in ambient temperature by adjusting the power in the 
>>> resister.  We don't even have to care if the crystal's temp-co is 
>>> nonlinear because we are using a very small temperature range, so 
>>> small it looks linear.
>>> 
>>> I'll build it.  Can you or anyone else subject a simple XCO 
>>> schematic?  Hopefully SIMPLE.   What I need is a design that can be 
>>> pulled down a few PPM so that I can raise it back with a bit of 
>>> heat.  I will have to be kept at a temperer above the hottest it 
>>> will ever get inside the house, maybe 100F.
>> 
>> See below or attached (hopefully).  L and C are chosen to resonate at 
>> the crystal frequency with XC and XL in the general vicinity of 100 
>> ohms to 1k ohms.
>> 
>> What you are proposing is a disciplined oscillator using the oven 
>> setpoint as the control input.
>> 
>> Best regards,
>> 
>> Charles
>> 
>> 
>> 
>> 
>> 
>> 
>> 
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