[RFI] Guidance on finding noise?

[Don Kirk]

 Scott (K9MA) asked "wonder if a two-turn loop a foot square could be made
to work on 160".

Hi Scott, I use various portable tuned loops for DFing 160 meters and 80
meters (see attached picture).

One is a 4 turn 14" diameter loop made with RG58 coax with a 1 turn pickup
wire (based on a design by W1FB), and the other is a 6 turn 13" x 13" loop
with a 1 turn pickup coil (PVC pipe construction based on a design by K2XT).

The 14" diameter loop is permanently tuned to 160 meters using a small
variable cap, while the 13" x 13" tuned loop uses a 365 pf air variable
capacitor and it allows me to adjust the antenna from the middle of the AM
broadcast band to just above 4 MHz.  Both of these designs are very
portable, but I also use a W1FB preamp with both of them when I am not
close to the RFI source (preamp is a dual band preamp for both 160 and 80
meter band).  I can pretty much hear anything with these loops that I can
hear with my 68 foot base loaded vertical that I use on 160 and 80 meters.
Attached is a picture showing these very portable antennas.

You can also see an example showing the immunity of the 14" diameter loop
to the touch of my hand on youtube at
https://www.youtube.com/watch?v=oMFMrOrAY3w&t=0s.  I just hold the 14"
diameter loop directly in my hand when DFing RFI, and I often just hold it
down at my side and rotate it for the Null.  Even the shape of the loop is
not critical, as it often is not round and often looks slightly oval, etc.

Just FYI,
Don (wd8dsb)

On Sun, Jan 12, 2020 at 8:29 AM K9MA <k9ma at sdellington.us> wrote:

> Just something to add to the database:
>
> I recently had a noise source appear on 160. As per my usual procedure,
> I re-transmitted the 160 noise to my cellphone and took a walk with the
> VHF tracker. (That way I can tell from the fluctuations whether I'm
> hearing the right source.) I found several noise sources nearby, but
> none matched.  I had an 80 meter rx loop I made for another purpose, but
> I could hear the noise with that, and tracked it to a neighbor's garage.
> I came from one of those LED "tubes", used to replace fluorescent
> lights, about 30 feet from my 160 rx antenna.
>
> While the 80 m loop worked OK, at 2.5 feet square it's a bit unwieldy. I
> wonder if a two-turn loop a foot square could be made to work on 160.
> I'm thinking of making it like my larger single turn loops, made of coax
> with a break in the shield. Has anyone tried that? Or would it be easier
> to just make an unshielded loop and feed it with a balun?
>
> 73,
>
> Scott K9MA
>
> --
> Scott  K9MA
>
> k9ma at sdellington.us
>
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