On Wednesday, March 23, 2011 4:55:40 PM UTC-6, Richard Fry wrote:
A few years ago there was some discussion on r.r.a.a. about helically-
wound, normal-mode monopoles, and the rather common expectation that
they had higher gain than a linear monopole of the same physical
height (and with other things equal).

I was always under the assumption that the helical whip was
less efficient than the same height whip loaded with a lumped coil.
I NEVER thought the helical whip had the advantage. And so far my
experience with the mobile whips seems to show that an efficient
lumped coil has the advantage.

A recent NEC-2 analysis of this topic might be of interest:
http://i62.photobucket.com/albums/h8...r_Monopole.gif

Where is the coil on the linear monopole? Seems to be a flawed
example to me. The helical example is loaded, but the linear is not?
What kind of comparison would that be to jive with the real world?
Of course, most will find that the location of the lumped coil
on a whip will effect efficiency and current distribution.
IE: the center loaded whip will generally have an advantage over
a base loaded whip.

A helical loaded whip can be a decent antenna, but I've always
had better results using the lumped coil.
Also, a helical whip needs some capacitive loading "IE: decent
length whip above the helical windings" to live up to it's
expectations. The helical whips with windings all the way to
the top doesn't do so well.

Also, the manner in which a helical whip is wound will effect
current distribution. It's best to maximize the windings near
the top rather than use a constant pitch the whole whip.
Much in the same manner that a lumped coil whip usually does
better with a center or higher mounted coil vs a base load.

If a helical winding was as efficient as a lumped coil, I
would not have converted my helical wound whips to lumped
coils. And if this were true, I would not have noticed any
difference when I did. But I did notice a difference.
So I think I will stick with the lumped coils.

I don't foresee a mad rush by the bugcatcher users to
convert to ham sticks any time soon. :/