[time-nuts] HP 10811

[ws at Yahoo]

Joe

The inner oven voltage needs to be stable! To better than 0.1V.
Unlike the single oven unit, the inner oven on the dual oven unit runs fine
at 15 Volts. It draws a couple hundred ma after warm-up.


One thing that improves the performance of a dual oven 10811 when being used
in a standalone application is to add a linear temperature controller for
it's the outer oven.
This makes the TC frequency change around a hundred times less sensitive to
room temperature variations, and by doing this it also so makes the answers
to your other questions about how best to box it up, a simple "it doesn't
matter", once the outer oven's temperature is set so the heater runs at a
nominal 5 to 6 Volts.

Another thing that can greatly simplify things and improve performance is to
keep the EFC voltage near zero volts and limit the range to 100mv or so
(~1e-8 freq change at 1Hz /Volt).

One of the more important ways to get great performance is by selection.
Many parameters will vary ten to one, and some things can vary as much as
100 or 1000 to 1 between units.

Here is the list of things I do to make a HP10811 dual oven oscillator into
a time-Nut quality stand alone Reference.

1) Select a unit with an ADEV of under 1e-12 from a 0.1 to 10 sec.
(about 1/3 of the ones I've tested)
2) Buffer the 10Mhz output
3) Use a linear 10V outer oven controller
4) Run-in until the ageing rate stabilizes, hopefully at under 1e-11 / day
 If not achieved after 6 months, re-start at #1 above.
5) Mount it on or near it's zero tilt axes
6) Run the oscillator's circuit on a *stable* low noise 12V supply
7) Run the inner oven on a stable and liner 15V supply
8) Rewire the inside. Besides removing ground drop problems, it also allows:
  a) Unseal the internal tuning nut by loosing it ~ 1/2 turn
  b) Readjust the mechanical freq, so the 10 MHz is within 1e-9 with the EFC
at zero. If retune is necessary then repeat step 4 above.
9) Connect the EFC to the wiper of a 10 Turn dial pot. Its range set to give
a freq change of 1e-8 full-scale (~100mv)(1e-11 / division).
10) Power the whole thing up with a stable, low drift, low noise, 15V, 2A
linear power supply. 
11) Leave it powered up, and running from an uninterruptible power source
12) Check and plot the absolute freq drift long term with a Tbolt GPSDO 
13) Check its short term freq with a TPLL.
14) Keep it away from any AC line noise sources, especially things with
transformers in them. 


Short Comment about rewiring inside at
<https://www.febo.com/pipermail/time-nuts/2016-February/095886.html>
a Picture at
<https://www.febo.com/pipermail/time-nuts/attachments/20160204/10b268f6/atta
chment-0001.jpg>


ws
  
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Joseph Gray Posted:

I have a spare 10811 that I want to setup as a standalone reference.
Since it is a double oven unit, should I put it and the power supply
in just a single walled plastic or metal box? Should I make air vents
or not? Going to extremes, can I put the OCXO inside a thick Styrofoam
box with no air flow at all (power supply external), or will this
cause overheating?

I may do a battery and float charger arrangement for the power supply,
so I can keep it running if the lights go out, or I want to take it
portable.

I know that the oscillator voltage needs to be very clean and stable,
but how about the oven voltage? Can I get away with a nominal 24VDC
from a battery, even while it discharges?

BTW, in case anyone was wondering why I haven't been on the list much
for quite a while, I have been busy taking care of my elderly mother.
She passed a month ago and now I am getting involved in projects
again. The first project is to clean and rearrange my work room. No
need to clutter the list with messages of sympathy. I'll pretend that
you sent them :-)

The 10811 has been on the shelf for a while, so once I get it running
again, I'll let it age for weeks (if not months) before adjusting it.
One advantage of being otherwise tied up lately, is that I have some
14-pin DIP Micro Crystal OCXO's that have been powered for months on a
breadboard, waiting for me to use one in a project. They should be
nicely aged by the time I get around to them.

Joe Gray
W5JG
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