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

Rick Karlquist richard at karlquist.com
Sun Feb 15 19:53:49 UTC 2009

Richard H McCorkle wrote:
> Hi Samuel,
> I suggest starting by downloading the component level information for
> the 53131A and 53132A from tha Agilent site at the following links.
> http://cp.literature.agilent.com/litweb/pdf/5989-6308EN.pdf
> http://cp.literature.agilent.com/litweb/pdf/5989-6307EN.pdf
> The 53132A document includes a schematic of the channel C board with
> parts list and may assist in getting you started.

I see that they have a factory select resistor that unbalances
the input slightly to keep the prescaler from oscillating with
no input.  This a simple, obvious "solution" to this problem.
It is also non-optimum, for three reasons.  It desensitizes the
prescaler, it uses a factory select part that may not work
consistently over temperature, and it still results in a range
of input power where the counter displays garbage.

In the 5334B C channel, I used a diode detector that turned on
the counter at a repeatable input power.  Thus you never got garbage
on the display due to low input power.  The detector used the
well known circuit where you bias the diode on with a few 100
microamps of DC and have a compensating diode that is not excited
by RF.  A difference amp subtracts the compensating diode voltage.
Simple, but effective.

It is also interesting to note that in 1987 I used the MB506 prescaler.
Here they have simply upgraded to the MB510.  Not likely to be
any better on noisy sources.

Rick Karlquist N6RK

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