[RFI] What antennas are good for HF DFing?

[Rob Atkinson, K5UJ]

Frank,

just an idea:  maybe a powdered iron rod with as many turns of wire around 
it as possible (i.e. a loop stick antenna, like what is found in most medium 
wave AM rx but bigger) would work?

the longer the rod the better.  maybe 12" long with ~ 150 turns on it.  You 
can get such a rod from ferrite material suppliers, maybe RF Parts, Amidon, 
Palomar?

for AM radio rx, these make antennas with pretty sharp nulls off the ends.  
I see no reason why they would not also have a null off the end in the 
direction of the source when used to rx mw hash.

I'd also see if an AM aircraft VHF rx picks up the noise when placed 
extremely close to the source.
it could be the source is so broad that is has radiated energy up into 
VHF--but it doesn't travel very far.  I use an AM aircraft rx and small yagi 
to df powerline noise.

rob/k5uj

From: "Frank N. Haas" <kb4t at arrl.net>
To: rfi at contesting.com
Subject: [RFI] What antennas are good for HF DFing?
Date: Sat, 12 Feb 2005 22:18:59 -0500


Dear RFI List:

I find myself spending a great deal of time attempting to locate 
interference in the range of 500 KHz to 8 MHz. Most of these signals 
originate from switching power supplies or electronic devices that behave 
like switching power supplies. The easiest signals to locate are those that 
don't radiate much. Instead they are conducted by AC mains wiring. 
Generally, the offender is located in the complainant's home and it's just a 
matter of using my handheld DC to Light receiver and walking around the 
house until the signal is the strongest. Then things start getting turned 
off until the signal disappears.

Signals that are radiated in this frequency range are more difficult to 
locate because it's pretty tough to lug around a 3 or 5 element Yagi for 2 
MHz. Since I have to do this several times a month, I need some suggestions 
on how one can DF signals that are so low in frequency. How do you 
professionals out there DF signals at such low frequencies???

In years past, many years past, I remember seeing "portable" receivers that 
were equipped with LOOP antennas that were used by mariners to DF broadcast 
band signals. Lines would be drawn on a chart using the bearings obtained 
from this setup. The point where the lines crossed was the location of the 
vessel. I wouldn't mind doing the same thing in reverse to locate some of 
these pesky low frequency interference signals. Are there plans somewhere 
for loop antennas of this sort?

Any help appreciated. Many thanks.

Frank N. Haas KB4T



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