[time-nuts] HP5065A environmental sensitivities

[Poul-Henning Kamp]

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In message <5741E08B.9080706 at rubidium.dyndns.org>, Magnus Danielson writes:

>The negative voltage switcher of A15 board should be replaced with a 
>suitable switcher, and some of the DC/DC switcher modules is built with 
>isolation, so it should allow for mounting two in parallel such that you 
>get both sides. PHK, have you checked this option?

Yes and no.

I think the +/- 20V *should* not matter, and the reason they currently do
is something a couple of well-chosen modern op-amps can take care of as
far as I can tell.

My hope was to design a couple of plug-in replacement boards to fix most
of these issues, while allowing A/B comparisons to the improvement can
actually be measured.

Basically:

A new integrator board, using a modern chopper/zero-drift op-amp.

A new AC amplifier, ditto.

Instead of the two diodes, put a modern "ideal diode" circuit and
two DC/DC converters on the first PSU board, producing the +24V and
a -15V rail for the rest of the instrument. (-15 instead of -20 since
it will be driving the opamps mentioned above.

On the second board, an opamp to drive the existing chassis-mounted
+20V series transistor from a _really_ good voltage reference (LM399)
and the most stable C-field drive circuit I can come up with.

But as I said, I'm just about to start building a new house, so my
time is limited for the next year or so...

If somebody else wants to take the lead, I'll happily assist as I can...

The "NextGen" project, would be to use a 48bit DDS chip to generate
the 60+MHz drive signal for the microwave, and a "geophone" ADC chip
to detect the modulation from the photo-diode, but that is even further
out...

-- 
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