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Half Size 40M rotatable dipole.
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 |
Half Size 40M rotatable dipole.
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 |
Half Size 40M rotatable dipole.
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 |
Half Size 40M rotatable dipole.
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 |
Half Size 40M rotatable dipole.
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. |
Half Size 40M rotatable dipole.
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. |
Half Size 40M rotatable dipole.
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. |
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