On Thu, 01 Sep 2005 22:24:56 -0000, (Dave Platt) wrote:

In article ,



- Build a multi-wire "fan" dipole, with one set of wires cut for each
band of interest. These are somewhat easier to trim (less
interaction between the wires) if the wires are fanned apart at a
broad angle, but it's quite possible to get them to work with each
wire simply hanging 6" below the next-longest one using simple
insulators of some sort. I use a three-wire fan dipole of this
sort, cut for 40/20/10, fed with coax, and it works quite respectably.

Can I use inulated 14 AWG wire and not use the fan method? Can I run them tied
together?

- Use a trap dipole (feeding with coax should be fine).


Vinnie S.

In article ,
Vinnie S. wrote:

Can I use inulated 14 AWG wire and not use the fan method? Can I run them tied
together?

The closer the wires are together, the greater the amount of
electrical coupling between them. As the amount of coupling
increases, the wires' ability to behave independently decreases... one
effect is that the useful SWR bandwidth of the wires becomes narrower.
The presence or absence of insulation won't have too much effect on
this change... some, but not a lot.

Eventually, if the wires are close enough together, they'll tend to
behave pretty much like one wire (the longest one) which is "fatter"
near the feedpoint, and you'll lose the ability to tune the
higher-frequency bands properly.

A separation of 4-5" inches seems to work pretty well. There are
plans in one of the ARRL handbooks which show a "fan" dipole made from
300-ohm twinlead, with one wire cut off short (and a second 300-ohm
section with two even shorter wires hung an inch or so below). I'd
expect this to have a narrower useful bandwidth on the shorter-wire
bands than one with a 4" separation.

I've even heard of people making these sort of fan dipoles out of
computer-type ribbon cable, in which the wires are only about a tenth
of an inch apart! I have no personal experience with this particular
version and don't how well this actually works in practice, but I have
a feeling it might be difficult to get to tune properly.

I suppose you could try making one with insulated wire, with the wires
tied together every few feet, and the shorter (lower) wires being tied
in loosely so that they sag downwards a few inches in between the
ties. This might separate 'em enough to allow for independent tuning.

If you can use insulators, do so, is my advice. You can make
insulators very cheaply from short lengths of 1/2" PVC irrigation
tubing.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

On Fri, 02 Sep 2005 00:07:52 -0000, (Dave Platt) wrote:


If you can use insulators, do so, is my advice. You can make
insulators very cheaply from short lengths of 1/2" PVC irrigation
tubing.

Great idea !

Vinnie S.

Vinnie S. wrote:
I have to do a inverted V config. I would be unable to run it horizontal. Can I
build one using simply a coax feed?

If you go with coax, you probably should use multiple dipoles (fan)
or a trapped dipole to obtain a low feedpoint impedance on your
bands of choice.
--
73, Cecil http://www.qsl.net/w5dxp


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