[RFI] RFI Direction Finding

Jim P jvpoll at dallas.net
Fri Feb 17 21:58:35 EST 2006

For MW and HF DFing I use a AM/FM/SW Sears
portable radio (we're talking a beast that takes 4- D
cells here) that uses a long internal ferrite loopstick
for the AM Broadcast and 2 - 6 MHZ SW bands.

The loopstick gives incredible nulls off the ends, making
it very easy to DF the offending source. Walk a few
blocks or half a mile and 'null' again and 'x' will mark the

This radio is also equipped with a meter, and *this* comes
in handy when measuring and comparing the strong signals
from a noisy power pole, standing about a foot away from the
'ground' wire and note how far over the noise drives the

I've also gone after noisy battery chargers using this simple,
inexpensive, reliable, self-contained, versatile 4-band radio
that allows me to easily track down those pesky HF
sources; walk the streets in the area looking for the stongest
signal area and you'll be within a couple of houses of the
source. I did this in my neighborhood where the electric
lines are buried in the alley and was able to find a battery
charger used for charging those electric scooters from

Many people will recommend shielded loops in conjunction
with a  hand-held SW receiver, but, that outfit may lack the
sensitivity that allows a bearing to be taken while standing
on the sidwalk outdoors at your QTH.

Your noise source, while noticably affecting your 40 M
reception is probably also broad enough to be picked
up below forty, like in the 2 - 6 MHz range.

I wrote more here, descibing how I have used a TV field
strength meter (these read the amplitude of TV signal
'synch tips') to find short-duration impulse noise sources
(like arcing power lines) in conjuction with a dipole cut for
TV CH 3 and held using a 4' insulated in a handle made
of PVC pipe:


Good luck with your noise DFing and let us all know
what you found and how you found it.

Jim P  -- WB5WPA --

References, Electric scooter noise accounts:



----- Original Message ----- 
From: "Paul Christensen" <w9ac at arrl.net>
To: <rfi at contesting.com>
Sent: Friday, February 17, 2006 2:40 PM
Subject: [RFI] RFI Direction Finding

> 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
> 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
> -Paul W9AC
> _______________________________________________
> RFI mailing list
> RFI at contesting.com
> http://lists.contesting.com/mailman/listinfo/rfi

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