On 11/2/2015 2:49 PM, Jeff Liebermann wrote:
On Mon, 2 Nov 2015 00:28:03 -0500, rickman wrote:

You are assuming it will maintain something remotely like a circle. I
don't see that happening. Have you worked with this stuff? Maybe what
you have is more pliable than the stuff I used.

I've worked with the vinyl dryer hose, but not the aluminum foil
variety. With the vinyl, I was using the helical "Slinky" part of the
hose as an HF antenna. As I mentioned, the steel spring got hot and
melted the vinyl.

Sure, there is nothing good about the slinky dryer tube you mention.
Steel has horrible conductivity with its high resistance *and* very
shallow skin effect. But even a copper wire of that small gauge would
not be effective in a transmitter loop antenna.


The actual inflatable antenna was a vertical
monopole, so I never even tried to make a loop, and am not sure it
will work. That's why I'm trying to recruit someone else to do the
dirty work. I guess I could go shopping and do it myself, but I'm
kinda busy this week (mostly recovering from the last 3 week of
overwork). I suspect that there might be problems if I use too much
air pressure. With the monopole, the hose would handle about 30 psi
before producing a leak. It thinks that's more than enough to inflate
the loop, but might not be enough to be self supporting, especially
with a capacitor at the top.

I bought a piece of dryer aluminum to use in another experiment (btw, a
four foot column does not create much chimney effect over a 100 W light
bulb) and they are stiff, too stiff to be worked by a balloon. Also
they bend by expanding one side and not the other. Once it is bent it
is a bit hard to straighten out. I am not trying to dampen your
spirits. I suggest you buy a short piece of this stuff and just bend it
by hand. Get a feel for it and see if you think this type of tube can
be manipulated by simple machinery. I think it will cost less than $10
to try this.


I don't mean fall apart necessarily, but just not be much like a loop
antenna. I think the hard part will be shrinking it back down and
keeping its shape. Proof of the pudding...

The optimum shape is a circle with square, hexagon and octagon shapes
being a tolerable facsimile. I guess the question is whether a random
pretzel shape will work. Dunno, difficult to simulate, but easy to
try.

The prevailing wisdom is the area is what matters. Given what I saw in
those videos which seem to show directionality in the plane of the loop,
I'm not so sure. That and the results people seem to get with helical
loop antennas make me think we don't really "get" loop antennas.


There are helically wound antennas that have a similar issue. I have
yet to see any equations to model them. I wonder if they work or not,
in the sense of any better than a simple loop.

One of the local club members build a 160 meter vertical rubber ducky
(helical antenna) with ground radials and ended up with a usable
bandwidth of about 2KHz. Keeping it tuned on frequency was a
challenge. I think it was only about 10ft high and reportedly worked
fairly well. I tried to model it with 4NEC2 but gave up for some
forgotten reason. I think it was my inability to model the ground
characteristics. Based on this example, I would say a loop would be
better because the grounding isn't part of the puzzle.

I don't have any equipment to date. I have a couple of projects ahead
of this if I decide to build something.

No test equipment? It's difficult to build anything without some
basic RF equipment. I can provide a basic shopping list if you would
like. My shop, which I've been told should be repurposed a museum.
http://802.11junk.com/jeffl/pics/home/slides/lab.html

You clearly have much more experience than I do. I wold barely know how
to use a SWR meter and don't have an LRC meter... I can't remember what
a grid dip meter is.

Sigh. I have 4 assorted grid dip meters. I can mail you one if you
would like to play. It's very handy for measuring the resonant
frequencies of any LC circuit or antenna. It's not very accurate but
will get you in the ballpark or at least tell you if you're too high
or too low in frequency. Like this, but with more paint chipped off
and the case missing. At least all the coils are there.
http://www.universal-radio.com/used/W483lrg.jpg
Note that it won't go down to 60 KHz although I tried making a coil
that covered the range.

Thanks for the offer. Let me get my other stuff out of the way and
maybe I'll take you up on this.

--

Rick