"Steve N." writes:

"Steve N." wrote in message
...

Rolf Brevig's choke is something I don't think I've seen before, but I
understand the concept. I can't tell, but I suspect it is common "1/4
wave
stub", no?

A 1/4 wave stub would work better, but be less simple to
fabricate. This design is trivial. It's just a coiled length of coax.

I also just realized that the choke is very similar to the Microwave
article's concept of simply opening the shield. I think that was your
point.

That was my point. But I now see that we're putting it at a high
impedence point, so the isolation is going to be far from perfect.

Anyway, my *real* point was that this was a useful antenna. Carry one
rolled up in your pocket and hang it from a tree to extend the range
of your HT. Cut one for 156.8 MHz and keep on your sailboat in case
you're dismasted. Etc.

73
LA4RT Jon

Jon Kåre Hellan wrote:
. . .
Anyway, my *real* point was that this was a useful antenna. Carry one
rolled up in your pocket and hang it from a tree to extend the range
of your HT. . .

I did a bit of experimenting along this line and found that any fixed
antenna hung from a tree was a poor way to extend range. As you probably
know, multipath propagation causes dead spots every few cm -- the cause
of "picket fencing" when mobile -- when you're in a marginal area where
a better antenna would help. Any fixed antenna is fairly likely to end
up in one of those dead spots. And additional gain due to height is
likely to be largely canceled by feedline loss unless you carry along
some large diameter coax.

What I've found to be the best VHF antenna for portable use in marginal
conditions is a telescoping half wave antenna like the AEA "Hot Rod" or
various imitators like the MFJ. They radiate as well as a J Pole, but
have the advantage that you can move them around to find a "sweet spot".

Roy Lewallen, W7EL