[RFI] finding stray RF

Cortland Richmond ka5s at earthlink.net
Sun Feb 9 11:31:30 EST 2003

There are a number of things you can build, buy or borrow, ranging from a
diode detector and earphone to a scanner with a "spectrum scope" display,
to $1600 calibrated broadband field strength meter (or even more complex
and expensive receivers and analyzers).  Between these extremes, there's
the $89 "Zap Checker."

I have some of each, courtesy of flea markets, 19 years in EMI, and E-Bay.

A simple RF field strength meter such as the Zap Checker or even just a
detector and meter, will tell you RF is THERE -- but it won't say what that
RF is. I was looking for local sources and thought I'd found one in my
thermostat. A Zap Checker said it was _hot_. But the EM-Eye with its AM
detector told me I it was RF from a nearby broadcast station. 

For what it's worth, a Radio Shack analog milliammeter with a diode
detector across it and a wire probe on one terminal will find stray
transmitted RF. Instead of a wire probe, coax from the meter terminals to a
clamp-on ferrite bead probe such as has been discussed here already will
let you troubleshoot current in individual conductors. If you have too much
signal, put a potentiometer across the coax and feed the tap to the meter.
It's not complicated.


Ed, AA9OZ wrote

> A month of two ago, someone made reference to a device that could be used 
> to detect stray RF in and around a ham shack.
> The construction of such a device was described in an issue of QST.
> Can anyone give me the reference to the construction article?

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