[time-nuts] What are HP High Stability Oscillators (Option 1D5 in 8720D VNA)

[David Kirkby]

I recently bought an HP 8720D 20 GHz VNA with options 010 (TDR
facility) and 1D5, which is the high stability time base. It's a
fairly old VNA (not supported since 2004), but it's not exactly a
dinosaur


Accuracy (23 deg C +/- 3 deg C) 10 ppm

The standard oscillator specs are:
Stability 0 - 55 deg C
7.5 ppm
Ageing per year = +/-3 ppm

The high stability time base, option 1D5 are:
Stability 0 - 55 deg C
+/- 0.05 ppm
Ageing +/- 0.5 ppm

Resolution 1 Hz.

What is likely to be the difference in design between the standard and
high stability oscillators?

It seems that while the optional timebase is more stable, this does
not appear to reflect in the accuracy of the instrument, which is
specified as 10 ppm. Perhaps that's due to the fact that the steps are
1 Hz, and the synthesiser can't generate exactly 1 Hz steps. I don't
know. You guys know more than me!

dave