[time-nuts] HP5065A C-field mods and optical unit mods

[cdelect at juno.com]

HP5065A C-field mods and optical unit mods

The contribution of the temperature coefficients of the fixed resistors
and the pot (which is a 21 turn bulk metal foil 10PPM/Deg C pot) show up 
as frequency errors as shown for several combinations.

Note that the pot does not cover the entire 2X10-9 frequency range.
There is a high, mid, and low switch setting that shorts both 1k,
one 1k, or neither 1k resistor that in conjunction with the pot allows
the entire range to be covered. This allows the pot to have a finer
frequency resolution

A- With only the 2.4K in circuit with the pot at zero Ohms a 1 Deg C
change
will cause a 2.8X10-15 frequency change.

B- With the 2.4K in combination with the pot at 1K a 1 Deg C change will
cause a 8.55X10-15 frequency change.

C- With the 2.4K in combination with the pot at 1K and both 1K resistors
in 
circuit a 1 Deg C change will cause a 3.99X10-15 frequency change.

If in example C you replace the pot with a 100PPM pot a 1 Deg C change
will equate to a 2.45X10-14 frequency change.

As you can see this circuit will work quite well in eliminating any power
supply related C-field changes.

Now the C-field coil is only partially temperature regulated by the 
ovens in the optical unit as they  regulate the lamp and cell
temperatures
and the C-field is not co-located. 

That is why I'm going to use the PC liquid cooler to actively regulate
the
temperature of the sealed enclosure I have placed the optical unit into.

Cheers,

Corby