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

Samuel D. [x86/CPC] sam at canardpc.com
Sun Feb 15 17:04:28 UTC 2009

Thanks for your answers.

About the components, I think my first prototype will use some very
well-known prescaler and amplifiers like Hittite HMC363 and Mini-circuits
ERA-1SM, only to validate the design. I will use a 100 MHz high-pass filter,
but overall, it will be a wide-band, low-sensitivity design, exactly like
the original option. 

But before thinking about the best components to use for the amps and the
divider, we need to know how to interface the prescaler with the counter.
There is some very important questions to answer :

 - What's the divider ratio used ? Perhaps /16 for 3 GHz, /32 for 5 GHz, and
/64 for 12.4 GHz, but we really need to be sure.
 - What's the gain of each one of the four amplifiers present ?
 - How does the counter aware about the option used ? There is no
"intelligence" on the option board, so, the counter may detect the type of
prescaler with some pull-up or pull-down resistors somewhere.
 - What is the exact pinout for the J2 connector ?

In order to get an answer, we need to find somebody with a genuine option
board willing to spend an hour for the project... 


-----Message d'origine-----
De : time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] De la
part de Rick Karlquist
Envoyé : dimanche 15 février 2009 03:47
À : Discussion of precise time and frequency measurement
Objet : Re: [time-nuts] DIY Frequency extension for HP Agilent 53181A,
53131A or 53181A

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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