On Oct 11, 3:35*am, wrote:
Hello all. I am looking at building a half size rotatable 40M dipole.
It will be approxiamately 10 metres long end to end. It will have a
loading coil in each leg with about 5 metres of wire wound on a nylon
former. My question is, where would be the best spot to mount the
loading coils? Half way along each leg, ie- about 2.5 metres from the
feed point or should the coils be mounted closer to the feed point? I
realise that this antenna will be inferior to a full size dipole, but
a half size one will fit where I am located.
Any constructive ideas or experience with loading coils would be
appreciated.
Cheers
Max

1/2 to appx 3/4 out from the center point is usually about the best
compromise.
You want to improve the current distribution, but at the same time
not get so carried away that the loss from the extra number of
coil turns needed outweigh that.
With no hat, 3/4 the way out is about as far as you want to go.
You could probably go a bit farther out if you use a hat on each
end. But myself, I'd probably still leave it at about 3/4 the way
out even with a hat. The typical hats used will not be too big
vs the wavelength on 40m.. IE: Four spokes of 3-4 feet long
is not a huge increase in capacitance for that band.
So I would not run the coil all the way at the end.
Reg Edwards old "vertload" program will let you see the best
point to mount the coil, but it does not deal with hats.
Only a single "stinger" whip. It will also tell you about
how many turns for the coil at the various positions.
Those programs are probably archived on some site.
A google search would probably turn them up.