[RFI] RFI Direction Finding

Cortland Richmond ka5s at earthlink.net
Fri Feb 17 19:24:00 EST 2006

Yes, do try a small shielded loop. Here's one design that works fine on my
VR-500 receiver:
It can be made with three or four RS parts (as long as they still sell
them!). It is important that at one end of the coax the center pin is left
floating and the center conductor is shorted to the shield. Also, there
needs to be a gap in the shield at the top, as shown. 
This loop does NOT work well on a TH-F7A; that HT's receiver needs a
near-50-ohm antenna. But on a super-sensitive wide band handheld like the
VR120, VR500, AR-8000 etc. a small loop will do the job. Even a Male BNC to
dual female banana plug adaptor with a loop of wire attached will work.
Simpler loops are possible; a piece of coax with the center conductor
connected to the shield a foot or so down the cable and the shield left
open at the end is also a functional loop -- and you can make one out of
any old coax you have laying around. It only needs to be strong enough to
hold itself reasonably vertical. 
Good hunting!
> [Original Message]
> From: Paul Christensen <w9ac at arrl.net>
> I am looking for a handheld DF unit capable of reasonable directivity on
> 40M. I have excessive (+10 dB/S9) power line noise centered near 7 MHz but
> the noise is not very detectable at VHF/UHF. I realize the gain will be
> for a handheld unit, but is there a device I can use to establish good
> directivity at 7 MHz within a reasonable size for walking or mobile

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