On Thu, 23 Apr 2015 11:56:18 -0700, Oregonian Haruspex
wrote:

How about a tethered helium balloon instead? This way you don't have
to worry about powering the thing. Bell wire will handle 100 watts all
day without turning into smoke.

I've been on a few field days that had helium balloon antennas. Like
all ham projects, we successfully duplicated every mistake possible:

- The wind blew the balloon and antenna horizontally. The downdraft
on the lee side of the hilltop finished the job by pushing the balloon
down further, and into the trees. I suspect a kite and a balloon
might have prevented this problem, but we never tried it.

- We didn't install a static bleeder on the antenna terminal. After
throwing a few lightning bolts, a bleeder to ground was hastily
fabricated to prevent vaporizing the receiver front end.

- A large part of the antenna tuning is the capacitance between the
antenna and ground. That can be tuned out easily with an antenna
tuner, but not so easily if the antenna is flopping around in the wind
with the capacitance changing rapidly. An automagic antenna tuner
helps, but is not capable of tuning continuously or at operating power
levels.

- The wind resistance of a 3 ft dia balloon is fairly substantial.
The air flow is turbulent. The result is considerable pull on the
antenna wire. I would have expected the wire to break. Instead, it
dragged the radio off the operating table and later caused the knot
holding the balloon to the wire to come apart.

- Helium is expensive. 1 liter of helium can lift about 1 gram.
If the 1/4 wave 160 meter antenna uses #16 AWG wire, which weighs;
40 meters * 11.6 grams/meter = 464 grams antenna weight
Add to that a 200 gram 3ft dia weather balloon for a total of 664
grams load which requires:
664 grams * 1 liter/gram = 664 liters
of helium required for neutral buoyancy. To get it off the ground, I
would add about 10%:
1.1 * 664 = 730 liters of helium.
Helium previously costs about $8/liter but is now running about
$20/liter thanks to the helium shortage. That's $14,600 for 730
liters. Are you sure you want to do this?





--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558