On Jan 23, 2019, at 6:32 AM, 'Dale Parfitt' [email protected] [KX3]
<[email protected]> wrote:
HI Wolf,
VK3YE could have done so much better from an efficiency standpoint without
making the loop any larger.
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.
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.
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..
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.
Dale W4OP
From: [email protected] [mailto:[email protected]] On Behalf Of 'Wolf
Hoeller, OE7FTJ' [email protected] [KX3]
Sent: Wednesday, January 23, 2019 4:57 AM
To: [email protected]
Subject: Fwd: [KX3] Urban stealth HF: Inside-the-backpack loop antenna?
Wayne,
a really good idea.
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
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
I would like the idea, to sit in an urban park with my backpack or similar on
my knees and make some contacts.
Wolf, OE7FTJ
Emergency Communications via Winlink Global Radio Email ®️
Am Di., 22. Jan. 2019 um 21:57 Uhr schrieb Wayne Burdick [email protected] [KX3]
<[email protected]>:
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
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Posted by: "Dale Parfitt" <[email protected]>
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