[time-nuts] DIY Frequency extension for HP Agilent 53181A, 53131A or 53181A

Rick Karlquist richard at karlquist.com
Sun Feb 15 02:46:46 UTC 2009


Max Skop wrote:
> Hi Samuel and all,
> Welcome to the group.
> I also have a 53131A and would welcome any way to enhance or upgrade the
> performance of this instrument. Please count me in on clone option parts.
> As can be seen from the picure of the 3Ghz option there is nothing special
> in its construction.  Just four stages of amplification and a divider.

In 1987, I was the project manager for the HP 5334B frequency counter.
In those days, we had a 1.3 GHz option called a "C channel".  I
evaluated various off the shelf dividers at the time and built
some C channel boards very similar to the one you are describing.
It is actually very difficult to make a prescaler that really works
well using off the shelf dividers.  The prescaler tends to be insensitive
to low frequencies.  Attempting to fix this with a lot of gain
(4 stages!) has the problem that any wideband noise from the source
is also amplified.  Off the shelf dividers are made to work in
frequency synthesizers where they have a clean signal from an oscillator.
They don't do well with general signals from noisy sources.
The HP 5386 used an HP made frequency divider that had "static"
flip flops instead of the "dynamic" ones in all the off the shelf
dividers.  It is the only prescaler I am familiar with that actually
works well.  The custom IC in it cost HP a fair amount just because it
was "home made" in the Santa Rosa fab, which was a money sink.

If you want to build your own prescaler, you might not want to copy
the Agilent one.  Unless you need the sensitivity, you would be
better off with less gain.  Also, you should choose a divider that
works well at the frequency you want to measure.  AFAIK, all OTS
dividers have an optimum frequency range, which varies from divider
to divider.

When testing prescalers, the thing to watch out for is that the
lower order digits will bounce around.  This is usually a symptom
of prescaler error, assuming that the source is stable.

Rick Karlquist N6RK




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