[time-nuts] Making a HP 10811 better

WarrenS warrensjmail-one at yahoo.com
Thu Mar 25 19:10:56 UTC 2010


I was wondering if there is any interest for a single oven HP 10811 
improvement design kit of some sort?

Background:
I am now using a double oven 10811 as the Freq reference for my own 
projects.
Some recent off line conversations made me realize that there are many 
advantages to using a single oven instead of a dual oven 10811 osc.
Among them are:
1) probable does not need separate floating PS to work good, due to it 
having better grounds
2) has accessible freq offset adjustment, The EFC input can be set to near 
zero for 10.000 MHz output
3) Does not need an outer oven driver
4) It can be opened up for simple internal mods
5) And most important, they are much more common for the average time nut.

The only disadvantages I know of is that they change freq more with room 
temp changes. Up to 1e-10 is what I've seen.
My idea of a reference is something that one does not have to worry about 
things like it's PS and room temp sensitivities.
I think where possible things like temp, PS. Load, Freq stability, etc 
should be made to have effects on its freq that are below the noise level, 
which is around 1e-12.

Here is my thought;

I know how to make major improvements to the 10811 so that the standard 
stuff does not have ANY measurable effect on its freq.
Nothing really magic, mostly simple things like secondary PS regulators, an 
outer oven heater wrap and controller, some internal span and reference 
voltage adjustments,
tilt it on its Zero G axes, add an RF buffer, isolate or have a less 
sensitive EFC input, a fine freq adjustment pot, and probable others once I 
get into it more.
The goal being if I can measure something that causes it to change freq at 
the a-12 range, fix it.

I am only taking about basic superficial things, I'm not knowledgeable 
enough to fiddle with its RF stuff which seems OK as is.
But I do know from my DVM design experience,  the way they offset the EFC 
has to have some major contributing factor to its 1/F freq noise, at least 
on some units.
It has long been my suspicion, that part of their noise grading process was 
actually selecting units that happen to have a low noise internal 6.3 
reference, The one used to offset the EFC.

AND YES I do know none of this takes care of aging. The best solution for 
that is to select a good one and Let in run continuously.
In my case aging does not matter much because I have it disciplined to the 
GPS thru a very slow loop.

Any additions things to consider  and comments welcome on or off line.
By the way, I already have a long list of thing one could do to it to make 
it worse, so probable don't  need any more of those ideas.

ws

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