On Dec 4, 1:26 pm, Cecil Moore wrote:
Owen Duffy wrote:
I suspect that it is a technique to try to maximise the current moment to
get the highest radiation resistance. They then build out the radation
resistance with loss to achieve a specification maximum VSWR for direct
feeding at the base with 50 ohm line.

It could also be a technique to move part of the
loading up to the top of the antenna. I once won
a CA shootout with a top-loaded junk box antenna
that, in EZNEC, looks something like this:

I think the main reason they do that is to improve current
distribution.
The tighter windings near the top make it act more like a
lumped coil which is raised from the base.
This should provide a more constant current level up the whip.
It's done for the same reason people raise the usual coils used
on a bugcatcher , or whatever. To improve current distribution.
And most don't add any extra loss on purpose.
Most add a extra small winding at the base to act as a
matching coil.
If you take one of those helical whips, IE: hamstick, etc,
and add a longer stinger whip, you will have a pretty decent
antenna.
I used a 20m hamstick on 40m, by adding a 4-5 ft stinger
and it worked very well. Almost as well as the typical
bugcatcher.
But I later rebuilt that antenna by stripping the helical windings,
adding a bigger "lumped" coil, and it was pretty much electrically
the same as a bugcatcher. It works all bands 80-10 now.
MK