[time-nuts] HP 106B quartz frequency standard...the story so far

[Jim Palfreyman]

Hi All,

Well I'm doing stuff and have had an interesting journey so far and thought
it was time to share it with people who get it. My girlfriend just doesn't
understand...

First I want to give thanks to Stan Searing and Steve Roberts who emailed a
scanned manual and to tvb for the offer to send one in the post.

Here is the journey so far...

I asked a question of this group over two years ago what would be a good
thing to measure ABSOLUTE time at high precision. After all, with all the
gear I had there had to be something. No one came up with a good answer.
After wandering back to my old University and talking to the Professor of
mathematics and physics there, his answer has obvious...you need to study
pulsars.

So I'm doing a masters in astrophysics studying pulsars and I'm measuring
the arrival times of the pulses of the Vela pulsar to a resolution of 10
micro seconds using a hydrogen maser. Pretty pissweak accuracy in our realm
I have to admit, but there is a lot more to take into account. The arrival
time is dependent on frequency and also on the "stuff" (i.e. molecules)
between Earth and the pulsar. This makes 10 micro seconds pretty decent.

But I digress...

The Uni chucked out a 106B and I grabbed it. Stan and Steve (both) provided
me with a manual and I've been working on this beast.

First I had to remove the leaking NiCd batteries. A quick check of the power
supply rails then showed plenty of non DC rubbish so the filter capacitor
was suspect. I replace the 1000 uF cap and things started working way
better.

The main power rail instead of being slightly under 18v was a bit over 21. I
think this is the Q3 "regulator" issue (the regulator being a transistor and
probably destroyed by the bad batteries and capacitor) - but this is not
going to be an easy one to replace - a 2N1701.

Anyway, I let the voltage rail sit and the oven heat up for a number of days
and adjusted the frequency with the course control (all the nice fine
control mechanics had been removed) as close to 5 MHz as I could.

Things seemed great until I noticed the frequency steadily increasing over
time. Not matter what I set the frequency it kept increasing.

So I started playing with the inner oven control. I noticed this could be
adjusted to modify the change in frequency from positive to negative. As I
write I'm trying to find the spot where the frequency is level.

As an aside, this 106B has an extra board in it to generate a 1 PPS signal
and can be set with a sync signal. (Which seems to have a 200ms delay -
which is unfortunate) - I thought this was a local Uni thing but talking to
Stan he seems to have the same modification.

Updates to follow...