[RFI] Handheld HF direction finder

Kenneth G. Gordon kgordon2006 at frontier.com
Sun May 18 18:38:30 EDT 2014

On 18 May 2014 at 22:19, Rich Hallman - N7TR wrote:

> On my ft-100 in the utv and a hustler 80 meter mobile vertical it's about 10
> over near the source.   Freq is 3900. But many other harmonics of the mix
> every 10 kHz, but 3900 is the loudest. 

OK. Then, IMHO, you will need an attenuator of some sort between the 
antenna and the receiver.

I would suggest that you build one of Tom Thompson's 24" in diameter 
"link-coupled" loops, and tune it for 80 meters.

The cost is very minimal and it took me all of an hour to build mine. It 
works extremely well. I am very grateful to Tom for designing it, and for 
publishing the info on the web.

I used an ancient three section BC band variable with some silver mica 
caps in parallel to enable me to tune my version of that loop on 80. 
Tuning is VERY sharp. This means you can de-tune the loop for much-
reduced sensitivity as you get closer to your source.

Using that loop, your FT-100, and taking several careful bearings, you 
should be able to pin-point a fairly close area where your noise is 

Then all you have to do is to walk up to it using some sort of small hand-
held AM radio which will tune to that frequency. Radio Shack sells such a 
small receiver. It covers AM/SW/FM frequencies and can be tuned to spot 
frequencies in the 80 meter band (and 40). It is about 4" high, by 5" 
long and about 1.5" thick.

Of course, that receiver has no "S" meter, nor any way to connect an 
external antenna to it, but if you are close enough to the source it may 
work OK.

I plan to build one of Tom's dedicated RFI receivers asap.

>   I think I sent a you tube video of
> what I'm seeing a few weeks ago.

Yes. You did, but I am not familiar enough with what I see there yet to 
tell you anything of any value about it.

Others here are FAR more expert at this sort of thing than I am.

Good luck, and vy 73,


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