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[Amps] 8640B sig gen TSPA

To: amps@contesting.com
Subject: [Amps] 8640B sig gen TSPA
From: "John T. M. Lyles" <jtml@lanl.gov>
Date: Wed, 6 Jul 2005 10:11:45 -0600
List-post: <mailto:amps@contesting.com>
The Hp 8640B is a superior instrument to the Wavetek 3000/3001 etc, 
but as someone pointed out, caveat is that the 8640B is painful to 
repair. It has a tunable cavity for the RF generator, explaining the 
spectral purity. The prices of these things have dropped over the 
years, used ones were about $1500 in the mid 1990s, and now they can 
be had for $300 if you are lucky.

Things to watch out for are noisy output attenuator (or burnt ranges) 
and a bad pot for the variable attenuator. This assembly can be 
removed as a unit, if you get underneath the unit. Depending on which 
model, sometimes the oscillator stops (on mine) at the ends of the 
freq bands, but it always restarts if I just move around the crank 
and come back.

I have the militarized black face version in the heavy yellow box. 
They are very easy to find since DOD has quit using them. It lacks 
the frequency lock feature that locks the osc to the counter 
timebase. It does have the freq counter, though, as if i leave it on 
for a long time, it is damn stable. The 8640A had a slide rule dial 
and lacked the counter altogether. Avoid that one.

Later, HP developed the synthesized 8642A and B, which had similar 
performance to the 8640 in most respects, but was much more complex 
and used microprocessors. It is a very heavy and deep unit, and last 
time I checked, was still supported, due to the DOD users. It has 
built in fault diagnostics and self test features.

73
John
K5PRO
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