[time-nuts] Making a HP 10811 and similar types better in the realworld Part I

Bob Camp lists at rtty.us
Wed Sep 21 20:43:48 UTC 2011


Just how good is the thermos bottle in this case? (as in degrees / watt).
You can get some very good vacuum ones and some pretty poor Styrofoam ones. 


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Perry Sandeen
Sent: Wednesday, September 21, 2011 4:20 PM
To: time-nuts at febo.com
Subject: [time-nuts] Making a HP 10811 and similar types better in the
realworld Part I

GM List,

Basic commandments of precision grade Crystal Oscillators. (1) It is both an
art and a science. (2)  The devil is in many details. Unbelievers suffer.

Here is the framework of methods that really work.  (Assuming a used unit)

1.  Make sure your power supplies are stable AND meet the low noise
requirements stated in the data sheet.  This means using something based on
the buried zener principle for both the heater, oscillator and EFC supply
using three separate circuits.  Hint: filter, filter, and more filters.

2.  The EFC voltage should be derived from something like a REF-10.

3.  The voltage references of all the supplies should be in a temperature
regulated housing.

4.  Wrap the oscillator in fiberglass and insert into a wide mouth thermos
bottle with the opening downward.

5.  Wrap that assembly in another 6 inches or so of fiberglass insulation
and still keeping the fiberglass filled mouth downward, place into a wooden
box of choice.

6.  Place box of choice  on concrete floor.

7.  Fire up oscillator.  Let it cook for at least two weeks.

8  After burn-in period use the EFC voltage to set the frequency to 10MHz
(An old Bourns 10 turn linear pot with a counter dial is ideal) using your
GPS or Rubidium standard using your favorite comparator.  Note dial reading
and record.

9.  Wait one week and repeat step 8.

10.  Wait another week and repeat step 8.

11.  After another week reset the frequency and compare the DIFFERENCES in
your recorded dial readings.  After the differences become close to the same
(EFC is non-linear) week after week one has a very stable oscillator that
can start to be useful.

Why this works

High stability oscillators do not want to be bumped or have their factory
set temperature changed.  They are not like a car engine that needs a
radiator.  The ovens are proportionally controlled.  On start-up all ovens,
proportional or not, will have over-shoot. Some more, some less.  An
inescapable fact of life.  

Cooling the exterior case of an ovenized crystal oscillator only causes the
oven(s) to come on more frequently.  When the heater current(s) go to a
minimum level, that is when the oven has reached its factory set-point and
is a happy camper.

The vacuum flask minimizes heat losses.  The interior and fiberglass
insulation prevents air current flow and add more insolation.

In part two I'll expand on the 10811 temperature problem and explain my
precision oscillator credentials,

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