[time-nuts] Making a HP 10811 better

[Bob Camp]

Hi

On a properly working crystal oscillator, EFC is essentially instantaneous at the "many seconds" level. The main delay you see is from the R/C time constant between the R's in the tuning attenuator and any bypass C's that are present. Time constants rarely get over 50 ms. Twenty * tau would only be 1 seconds at the 50 ms case. There's not much settling left to do after 20 time constants. 

Bob

On Mar 27, 2010, at 1:21 PM, WarrenS wrote:

> 
> Pete2
> 
> Addressing your first question only, I'll let the experts address the why.
> 
> Yes, I 'think' it does in principal, I would not guess on how long it takes though.
> But
> I have not checked that close to be sure.
> I'd never do something that gross during the middle of a test that I was trying to see 1e-12 things.
> I do that first thing, long before the high resolution test starts and then let things resettle before proceeding.
> Any change in cable position or the Osc moving a bit in its Box or a dozen other things could also change it that much, including temp gradients in the box, so Don't do that if you want 1e-12 results.
> Use the wedge, that I have tested, and is completely reversible and repeatable at those levels.
> I have noticed that the OSC will even take a long time to resettle  (hrs+ ) if the EFC voltage is change a lot and then put back.
> Which is why I limit the clamp voltage of my Tbolt to typ + - 100 mv or less from its nominal.
> 
> ws
> 
> ********************
> 
> 
>> Warren,
>>    If you turn over an oscillator, is the frequency change
>> completely reversible (to your "under 1e-12 resolution") when it is
>> restored?  Thinking aloud, if an hour-glass is turned over twice, the
>> final level will be the same, but the grains will be mixed.  A quartz
>> crystal, however, is solid, so hopefully nothing actually moves.
>> Presumably the zero-G axis is with the axis of oscillation at 90
>> degrees to gravity?
>> 
>>    Peter (the "other" one :-)
>> 
> ***************************>
>> 
>>> Another thing I use it for is to test high resolution Freq meters.
>>> Using a calibrated wedge that I can then slide under one edge of the zero-G
>>> Osc box, I can
>>> make small, variable, repeatable, freq changes of under 1e-12 resolution,
>>> something pretty hard to do otherwise.
>>> If I want to make BIG changes like 1e-10, I can rotate the box on any of its
>>> sides and still use the wedge,
>>> and for a quick check of new equipment, I just turn the box over which then
>>> gives a couple of parts in 1e-9 freq change.
>>> It makes a weird but simple and indispensable variable freq source that is
>>> useful for many things, such as checking the LOOP TC of a TBolt.
>> 
>> 
> 
> 
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