[time-nuts] Making a HP 10811 better

WarrenS warrensjmail-one at yahoo.com
Sat Mar 27 23:52:58 UTC 2010


Bob wrote:
>EFC is essentially instantaneous at the "many seconds" level. There's not 
>much settling left to do after 20 time constants.

ALL  mostly true, although I have not seen any TCs as long as 50 ms.
EFC inputs on most Osc I've tested, including the 10811, are essentially 
instantaneous at <100us TC. (BW > 2 KHz)

BUT
I find it amazing how a few true statements of basic principal can be used 
to counter the facts.
I should of made it more clear, I was NOT talking about TC settling.
The long "resettling" time of hrs I was referring to is of a similar effect 
as turning the unit off for a while and then back on.
I suppose that according to your book formula, that should only take 20 
seconds also to come back to within 1e-12.
Maybe the problem is that the Osc does not read the same books,
OR maybe the problem is just that some of us are getting more performance 
from them than they were ever designed to give,
and at that level there are a few new unexpected and unknown secondary 
effects.

ws

*******************
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
******************
WarrenS wrote:

> I should of also said; when care is taken, turning the Osc unit over is 
> repeatable,
> if just looking at a graph plot where the resolution is several parts in 
> e-11.
>
> 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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