Freq counter max input voltage-boatanchor safe?

Steve Harrison ko0u at OS.COM
Wed Aug 11 15:28:38 EDT 1999

At 12:34 PM 1999-08-11 -0500, Bruce Brackin wrote:
>Have recently acquired a nice frequency counter for bench work on my
>multiplying boat anchors.  Having problem finding specs and manual and
>don't want to blow the front-end away with too high of voltage from tube
>sets.  Anyone familiar with the max input ratings for a Beckman
>Industrial UC10A universal counter or similar model?  I can make up a
>voltage dividing probe but want to be on the safe side. Works well to
>about 100 MHz and I want to keep it that way.  Thanks in advance.

Assume it's 0 dBm, one milliwatt. Some may be more sensitive and when
overdriven, could generate harmonics internally.

Main thing is to keep the coupling to the tested circuit as light as
possible so you don't pull its frequency. Even if it's not an oscillator,
you could detune it's resonant tanks and cause it to generate spurs or
other harmonics that it normally doesn't do. Often, a cable to the counter
with center conductor shorted to the shield by a coiled cliplead waved
around the circuit-under-test is sufficient. When I don't know the actual
power from a Unit-Under-Test, I might try a small potentiometer across the
counter, or a very small coupling capacitor like a couple puff.

73, Steve K0XP

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