[Premium-Rx] HP 8649B?

[John Miles]

Yeah, the 8640B is (or at least was, for decades) pretty much the gold
standard for receiver testing.  You won't have any leakage problems with a
properly-sealed 8640B.

On the non-option-2 instruments, the bandswitch still has a 512-1024 MHz
position that will cause the frequency readout to be doubled.  That's all it
does.  This feature allows you to read the frequency when using an external
doubler on that band.  As far as external doublers go, the Mini-Circuits
FD-2 for $40 is a good choice, or you can sometimes get the HP-recommended
11690A for 2x-4x that on eBay.

The 8640B's frequency counter is only specified through 550 MHz or
thereabouts, regardless of option.  Even on an option-2 instrument, its
readout is "doubled" digitally when the 512-1024 MHz band is selected.

-- john KE5FX
  -----Original Message-----
  From: premium-rx-bounces at ml.skirrow.org
[mailto:premium-rx-bounces at ml.skirrow.org]On Behalf Of jan at skirrow.org
  Sent: Wednesday, August 20, 2003 9:04 AM
  To: Henry Kolesnik
  Cc: premium-rx at ml.skirrow.org
  Subject: Re: [Premium-Rx] HP 8649B?


  Hi Henry ...

  The counter itself goes to 1024 on all units as far as I know. But, in
effect, on the top setting of the range switch (512-1024) the counter reads
correctly within this range as you turn the frequency knob, but the
frequency output is half what the counter reads. I assume it was done this
way because the counter part can be used as a stand-alone 1GHz counter thru
a front panel bnc. But ya gotta have that INTERNAL doubler for the top band
to output correctly.

  I have never had problems with RF leakage - in fact the 8640B is a very
well sealed unit. I suppose that if someone damaged the shielding gaskets on
the various RF boxes, it might start to leak. Also, I use double shielded
coax for my interconnects.

  Jan
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