RFI Direction Finding System

In 2007 our local radio club was discussing some RFI problems, when we thought it would be a good idea to get a system for tracking down power line noise or other interference. At first, we thought about a commercial unit, but then realized that our handhelds, notibly one owned by the club, could get the VHF aircraft AM band. This is a good freqency and mode for tracking down electronic noise.

Antenna user


The antenna was originally meant to be hand-held with the extension behind the reflector. Rene, N6NRN was the first member of our club that used it and he found it unwieldy. He added the great mast assembly that makes it much easier to elevate and turn to track noise.

The antenna is designed for 135 mhz. There are plenty of articles on the web about cheap antenna design. This one was choosen for easy construction, and no complicated feed matching hardware.

The antenna is built from hardwood stock, aluminum tubing and a short chunk of fibreglass rod from a junked quad spreader. I was lucky enough to have antenna parts in the stockpile and I found a quad spreader to supply the short rod used at the feed point along with tubing the sleved outside of it. Some other basic tubing provided the reflector and director elements.



It can be disassembled and packaged in one unit. It's not particularly small or light, but it can be carried around or passed on to whoever needs it.

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