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

the farther out you can get them the better it will usually work, adding
capacitive loading hats on the ends of the elements will also help and
increase the bandwidth.

wrote in message
...
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

On Sat, 11 Oct 2008 01:35:34 -0700 (PDT),
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

Here is the install info for the 40M add-on for the Cushcraft A3S
Beam.
http://www.cushcraft.com/support/pdf/A743_451.pdf

I have been happy with its performance and durability. I expect you
can glean some info from the pictures.

John Ferrell W8CCW

On Oct 11, 9:54*pm, "Dave" wrote:
the farther out you can get them the better it will usually work, adding
capacitive loading hats on the ends of the elements will also help and
increase the bandwidth.

Hello Dave,
I was wondering about capacity hats. Don't know much about them or had
any experience with them. Will have a look on google.
Cheers
Max

wrote in message
...
On Oct 11, 9:54 pm, "Dave" wrote:
the farther out you can get them the better it will usually work, adding
capacitive loading hats on the ends of the elements will also help and
increase the bandwidth.

Hello Dave,
I was wondering about capacity hats. Don't know much about them or had
any experience with them. Will have a look on google.
Cheers
Max

the cushcraft 40-2cd and the xm-240 use them just after the loading coil.
They can also be mounted at the tip of the elements. They use two 18-24"
long aluminum rods in an X configuration. More rods, or adding a wire
around the tips adds more capacitance.

On 11-Oct-2008, wrote:

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Subject: Half Size 40M rotatable dipole.
Date: Sat, 11 Oct 2008 01:35:34 -0700 (PDT)
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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

Where you place them is probably not too important to the performance but
the inductance needed increases as you move away from the center. The
center impedance will be lower than the nominal 72 ohms. EZNEC is good
for evaluating the size of inductance and effect on center impedance. Reg,
(SK) G4???, used to have programs, where you could plug in lengths and
inductances and get answers about F and Z. I believe someone on this
newsgroup archived his programs.

73. Ken Fowler, KO6NO

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.

On Oct 11, 12:50*pm, "Dave" wrote:


the cushcraft 40-2cd and the xm-240 use them just after the loading coil.
They can also be mounted at the tip of the elements. *They use two *18-24"
long aluminum rods in an X configuration. *More rods, or adding a wire
around the tips adds more capacitance.

The tips is a better location for the hats. You get some degradation
if you
mount the hat just above the coil.
You can check W8JI's mobile antenna info for the why's..
BTW, you generally will use the same techniques for these as you
would a mobile whip..
A half size dipole is basically just two mobile whips end to end to
make a
dipole. All the techniques used to maximize mobile antenna performance
can be applied to half size, or smaller dipoles.