[Elecraft] [KX3] Urban stealth HF: Inside-the-backpack loop antenna?

[Wayne Burdick]

Wish I had time to build one of these myself! A few other things in the queue....

Wayne
N6KR


> On Jan 23, 2019, at 6:32 AM, 'Dale Parfitt' parinc1 at frontier.com [KX3] <KX3-noreply at yahoogroups.com> wrote:
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> HI Wolf,
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> VK3YE could have done so much better from an efficiency standpoint without making the loop any larger.
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> 1. Flat metal stock is not as efficient as round stock (of the same circumference) because current crowding at the edges of the rectangular stock makes it appear smaller in surface area.
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> 2. A much lower D capacitor such as a dual gang air variable with the gangs in series (to avoid resistive losses in the bearings) or  a butterfly would also have aided in  higher efficiency.
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> 3. Copper would have helped efficiency  somewhat with its lower RF resistance and ability to be soldered  versus mechanical connections, but that is partially offset by aluminum’s larger skin depth. Of course copper is heavier and more expensive, but in tube form the weight issue could be minimized..
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> Just some thoughts. Again, the VK1OD calculator allows one to make precise efficiency measurements so even small improvements can be measured.  As an example, the difference in efficiency between using  braided coax as the loop radiator versus hardline or copper tubing is readily apparent. For the same diameter loop and same conductor diameter, a narrower bandwidth  means higher efficiency.
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> Dale W4OP
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> From: KX3 at yahoogroups.com [mailto:KX3 at yahoogroups.com] On Behalf Of 'Wolf Hoeller, OE7FTJ' wolf.oe7ftj at gmail..com [KX3]
> Sent: Wednesday, January 23, 2019 4:57 AM
> To: KX3 at yahoogroups.com
> Subject: Fwd: [KX3] Urban stealth HF: Inside-the-backpack loop antenna?
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> Wayne,
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> a really good idea. 
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> Have a look at VK3YE's youtube channel for his experiment to put a loop antenna in (frame of) a notebook bag. https://www.youtube.com/watch?v=BC5lFbLqaeg
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> Another good idea for a stealth antenna has the spain company Inac. Here is the suitcase with a loop inside the frame: https://www.inac-radio.com/MAK721PRO
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> I would like the idea, to sit in an urban park with my backpack or similar on my knees and make some contacts. 
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> Wolf, OE7FTJ
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> Emergency Communications via Winlink Global Radio Email ®️
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> Am Di., 22. Jan. 2019 um 21:57 Uhr schrieb Wayne Burdick n6kr at elecraft.com [KX3] <KX3-noreply at yahoogroups.com>:
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>> 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. 
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>> 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. 
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>> 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. 
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>> Any other antenna suggestions?
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>> Wayne
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>> N6KR
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> Posted by: "Dale Parfitt" <parinc1 at frontier.com> 
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