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 _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.