[time-nuts] Making a HP 10811 better

[Bob Camp]

Hi

The 10811 should respond quickly enough that a few minutes (5 ~10) between steps should  be plenty. If you stretch it out to far, things like aging, retrace, and ambient change can get into the data. Always return to your original resistor value to confirm that drift hasn't gotten in the way. If you decide to add more insulation, you may need to change the DC gain of the controller to compensate.  Also remember that DC gain, thermal gain, and set point all interact with each other at some level. A full optimization would attack all three. If you are going to do this to an OCXO, the 10811 is a pretty good candidate. It's made with leaded parts and put together with screws. No nasty SMD's or welds to get past. 

Without a temperature chamber of some sort,  making sure you have improved things can be difficult.  

Bob


On Mar 29, 2010, at 7:19 PM, Neville Michie wrote:

> I agree with leaving well alone,
> But I had a HP10811 which had no EFC control.
> I agonised about why this would be and bought a few varicaps,
> - I could not find suitable current sources and I had resistors.
> When I opened it I found the junction of the varicap diode,
> the oscillator capacitor and a resistor was dry. No solder at all!
> When it was soldered all worked well. Another unit was inspected and it had a lousy
> joint in the same location. The serial numbers of the two units were years apart.
> Now I am more confident with them I am thinking of trying to reset the oven temperature
> to suit my ambient temperature, the aged crystal and the drift of the thermistor and resistors.
> I may even lag the HP10811 with some insulation to reduce the internal temperature gradients
> and reduce the oven power.
> The method would be to use an external resistor which would be set to several likely values
> increasing the temperature past maximum frequency, then the same values decreasing the temperature.
> An hour or so at each temperature. Then a least squares regression to a parabola which
> should show the best value.
> 
> cheers, Neville Michie
> 
> 
> 
> 
> 
> On 30/03/2010, at 9:49 AM, Mike S wrote:
> 
>> At 05:59 PM 3/29/2010, WarrenS wrote...
>> 
>>> Bert wrote: >"would not feel comfortable tearing into the unit."
>>> 
>>> I tend to agree, First rule is "do no harm",
>> 
>> I've got this rule that says "If I don't know what the insides look like when it's working, I won't know what to look for when it breaks." :-)
>> 
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