On 11/1/2015 9:27 PM, Jeff Liebermann wrote:
On Sun, 1 Nov 2015 18:31:55 -0500, rickman wrote:

When you say dryer hose, you mean the corrugated aluminum tube that is 3
or 4 inches in diameter.

Yep. Just like the stuff in the links provided.

That might work for a loop antenna, but I
think the corrugations are hard to collapse once you expand them. So I
doubt it will work as the tuning element unless you simply change the
shape of the loop rather than keeping it a circle with an adjustable size.

The bungee cord down the middle is suppose to help collapse the hose.
I must confess that I haven't tried it. If that doesn't work, then
some elastic cords. If that fails, a nylon rope and some external
springs.

I used some of this stuff in a larger diameter to connect a humidifier
and it was flexible enough to extend and shape, but didn't go back
hardly at all.

Yep. It won't go back by itself and needs some additional help.
Anyway, if you want to get your picture in QST as the building of the
worlds strangest and probably cheapest loop antenna, here's your
chance.

Ok, so if you can force it to shrink with springs or ropes or whatever,
then something will be needed to force it to expand again. I'm having
trouble seeing how this will work without the antenna losing all shape.
These tubes are just not really easy to manipulate. They are intended
to be bent once with more than a little force but more importantly very
controlled force.

I'm not sure the inductance will change all that much. I have never
seen a calculation for the inductance of an accordion. It may have a
rather limited tuning range compared to a typical variable cap. At
least the frequency will scale the right way with size. Smaller loop,
lower inductance, higher frequency which will keep the radiation
resistance high.

--

Rick