[Test-Equipment] HP 8640A - new owner

[gil smith]

Hi Arthur:

>I have Ser No 1245A  00103.

My serial is prefix 1550A, which is later than yours, but earlier than my
manual.  It sounds like Kees has an earlier manual that may describe our
units better.  In my manual, the attenuator does not have the small tick
marks on the outer edge of the dial like my unit has, and it does not have
the ivory-colored "band" -- it looks like it just has a single index line.
So I think I have the same attenuator as you do (see attached -- pic may
not make it to the list).


>Please get back to me & let me know if your manual makes mention of how to
use
>the painted index on the fornt panel combined with the autoranging options of
>the output meter.

The manual simply says to select the output level desired (eg: -30 dBm),
and use the vernier (center knob) in the top 10 dB of its range for optimum
operation.  It says the vernier has an 18-dB range, and that the meter
reads the actual output.

Now my attenuator (and I think yours as well) has this ivory-colored "band"
as opposed to the single index line shown in my later-model manual.  It is
a thick band for the upper 10 dB (the optimun range), and a thin line for
the lower 8 dB.  There is a small ivory-colored index line underneath the
main dial, which moves with the vernier control to indicate the actual
vernier position within the band range.  This should correspond with the
meter, I would presume.

So I hooked up my 141T/8554L/8552A spectrum analyzer, and adjusted the
internal 30MHz cal signal to lie exactly a graticle mark.  Then I put the
8640A on the 32 MHz range, dialed in about 30 MHz, set its attenuator to
-30 dBm, and connected it to the SA.  I used the 8640A's attenuator vernier
to set the signal to the same graticle line on the SA -- the index line
that moves with the vernier control (under the atten dial) lined up exactly
with -30 dBm (as shown in attached pic).  The meter had autoranged to the
0-10 scale, and indicated 0 dBm, which I presume is the delta from the
attenuator's range setting of -30 dBm.  So it all seems to make sense to
me.  Does your unit work differently?  This strange
atten-range-band/vernier-index-line is a bit confusing, but I guess it gets
the job done.  And the meter seems accurate, at least in my quick test.


>I'm getting a sense of why the 'B' model is more commonly found. HP likely
>bought up all the 'A's & sent them to the dump!!!

I think the A model is a fine unit, but the B had a way to lock to an
external reference, which may be handy.  My 8640A seems to drift down
slowly in freq, compared to several counters I have here.  It would have
been nice to lock it to the high-stability timebase in my 5345A.

gil



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;  vaux electronics, inc.             480-354-5556   
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