Please note that this question refers to the branded "Thunderbolt E"
GPSDO, in a silver coloured case with blue label and using a single 24V
supply,
and not the gold coloured "Thunderbolt" that is often found marked "Rev E".
Whilst testing a Thunderbolt E I've observed that the frequency of the
10MHz output is affected by the load impedance.
Switching a counter input impedance from 50ohms to 1Mohm for example will
decrease the frequency around 1 part in 10^9, and this is reflected in a
consequent increase in the DAC voltage over the course of a few minutes with
the frequency recovering at the same time.
Similarly, with the frequency steady with a 1Mohm load, switching to 50ohms
will increase the frequency by a similar amount with the DAC voltage
decreasing to provide correction.
I'm familiar with the concept of frequency pulling in oscillators but
would have expected the Thunderbolt E output to be better buffered than this,
it's certainly not something I've experienced with the gold cased
Thunderbolts.
Before I start probing any deeper I'd be interested to hear if anyone else
come across this with the Thunderbolt E.
Regards
Nigel
GM8PZR
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