[Elecraft] Urban stealth HF: Inside-the-backpack loop antenna?

[David Gilbert]

Here's another idea.

Run a wire inside your shirt from one cuff across your back and down to 
the other cuff.  Wrap loading coils around each arm just above the 
elbow.  Feed the "dipole" in the center at the back of your neck.

I did a quick model (assuming your arms are held straight out) with 5.5 
feet total length and 2200 inductive ohms for each coil, with each coil 
30% from their respective ends of the wire.  It "resonates" at around 
14.15 MHz, but with only about 0.4 ohms real feedpoint impedance.  I 
assume it would take some sort of extra matching network to bring that 
up enough that a KX2 with the internal tuner could drive it.

Ignoring the effect of a person's arm, another quick calculation says 
that the arm coils would need to be roughly 11 turns of 10 gauge wire 
3.5 inches in diameter ... unless I made a mistake, which is quite 
possible.

It would bring new meaning to the term "compromise antenna", but I bet 
it would be more effective than a super small loop the size of backpack 
frame.

73,
Dave  AB7E



>
>
> On 1/22/19 12:57 PM, Wayne Burdick wrote:
>> I’ve engaged in plenty of ultralight HF pack operation, with a KX2, 
>> AX1 antenna and a dragged counterpoise. In wide open spaces it’s a 
>> blast. But urban settings with dogs, wire-eating cacti and 
>> overzealous Neighborhood Watchers can distract from one’s radio 
>> experience.
>>
>> So, just for grins, I’d like to try something completely incognerdo: 
>> no visible antenna. A small remotely tuned loop (say 12” diameter) 
>> would seem to be the best choice, as it would fit entirely inside a 
>> small backpack. It could have  modest efficiency while not requiring 
>> a counterpoise wire. Rigid 1” copper pipe formed in a square would be 
>> convenient to deploy.
>>
>> The loop would be only 6 to 8” from soft tissue, so you’d want to run 
>> QRP, of course.  OTOH, we’re talking about HF. A cellphone by your 
>> ear is probably worse.
>>
>> Any other antenna suggestions?
>>
>> Wayne
>> N6KR