DaveM wrote:
Arnd,
There is some really good info on the HP oscillator at
http://www.realhamradio.com/GPS_Frequency_Standard.htm, which describes uses
for the HP Z3801A GPS Receiver/Time Standard. The page at
http://www.realhamradio.com/z3801a-turning-point.htm gives you some really
great info on setting the crystal turning point temperature for the best
stability. This will help you to understand your questions about the
thermistor also. The oven isn't set to a standard temp, but to the best
temp that puts the crystal in the middle of its curve. The thermistor is
spec'ed at 100K @ 25C and 9.93K @ 80C. You'll have to shop around for a
suitable replacement, keeping in mind the physical size of the thermistor.
[...]

Hi Dave,

thanks a lot for your reply! And also to Fred for his remarks.

The information regarding the temperature calibration is very helpful. I
found a replacement thermistor, which seems to be suitable: 83K @ 25C,
10.24K @ 80C, reaction time 0.7s, size 1.5mm diameter.

As the HP 10544A uses an AT cut crystal I assume that I have to
calibrate for a frequency minimum (according to the above mentioned
website). As the HP 10544A contains a 10 turn variable resistor instead
of a hand-picked resistor, calibration should be quite straight forward.

Thanks again, best regards, 73,
Arnd

--
Arnd Gronenberg
EMail:
HAM: DJ9PZ / AB2QP