Re: FS: HP 432A c/w head and cable

Andy Talbot <andy.g4jnt@...>

Ahhh - so that explains a few things that felt wrong. I was wondering
how the DC substitution techniqe could possibly be made stable enough
using thermal heads to measure down to -50dBm, even using the latest
chopper stabilised opamps etc. And to do it so well just a decade or
so later.

Will go and find the AN64s now...

Andy G4JNT

Sorry to cross swords etc, but the 435 etc. are quite a different
breed to the 431/2 series and although the 435/6/7/8 etc do have a
second thermocouple, it is only concerned with temperature
balance, not a dc substitution like the 431/2 meters.

The thermocouple sensors benefit for much better stability than
the thermistor sensors due to ~20 years design improvement - the
new diode sensors are another order better still in terms of

Regarding the zero drift of the recorder circuitry, I think that
you will find this to be directly related to the sensor thermal

The old HP AN64-1 through -3 gave a considerable amount of info on
the various systems. I believe it has been re-written and is
available on the net.

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