I'm Limited To An Antenna On The Front Of My House. Out My Window I Made A Simple !/4 wave Verticle Dipole. Would A 1/2 Wave Simply Be Twice The Length, Using 462/f Mhz, And Would There Be An Advantage With A 1/2 Wave Over a 1/4 Wave ?
Thanks

Here's a link to a very fine 2M j-pole, easy to build and excellent results.
http://www.arrowantennas.com/j-pole.html
After copying the picture with the element lengths, click on "Instructions"
on the bottom of the page for the rest of the info.
A 1/2 wave will "get out" better than a 1/4 wave.
73
Richard WB8KRN


"WolfMan" wrote in message
t...
I'm Limited To An Antenna On The Front Of My House. Out My Window I Made A
Simple !/4 wave Verticle Dipole. Would A 1/2 Wave Simply Be Twice The
Length, Using 462/f Mhz, And Would There Be An Advantage With A 1/2 Wave
Over a 1/4 Wave ?
Thanks

Hi

On Mon, 27 Sep 2004 16:31:40 GMT, "WolfMan" wrote:

I'm Limited To An Antenna On The Front Of My House. Out My Window I Made A Simple !/4 wave Verticle Dipole.
Would A 1/2 Wave Simply Be Twice The Length, Using 462/f Mhz, And Would There Be An Advantage
With A 1/2 Wave Over a 1/4 Wave ?
Thanks

I'm not exactly certain what you've built - is each 'leg' of the
dipole about 19" - in that case you have a half-wave dipole.

The good thing about a half-wave dipole is that the impedance at the
centre of the dipole is a good match for your feeder & radio. If you
change the length of the dipole 'legs' then you'll get a poor match at
a half-wave per leg - but should get a good match again at 3/4
wavelength - but by that time the thing's getting cumbersome.

If you want something like a dipole but with more gain try a single
'quad' element, or maybe a 'slim-jim' type of antenna....

Alternatively a commercial mobile whip (say a 5/8th) with a suitable
ground plane might improve things for you - all depends on what you're
trying to achieve...

Regards
Adrian G0THW
Suffolk UK

"Richard Heindel" wrote in message
...

A 1/2 wave will "get out" better than a 1/4 wave.

Except, of course, for the little detail that Adrian alludes to. Assuming
your dipole is 19" on each side, then doubling it to 38" on each side will
cause a problem -- the feed point impedance will be wrong. You will need to
do some impedance matching in order to get your RF into the antenna in the
first place. It's fairly tricky to do that without incurring noticeable
loss, but once the RF gets into the antenna, it will work better.

HOWEVER, if you have a dipole whose total length is 19", then doubling it so
it is 19" on either side will make it a whale of a lot better. A doublet
only 19" long in total is not only too short to resonate, but the feedpoint
impedance will prevent most of your RF from ever getting into the antenna in
the first place, so the performance of the system will be dismal.

A half-wave dipole, on 2 meters, one 19" on each leg, is a very good
antenna, providing you can take the feedline away at approximately right
angles to the antenna. Most of the other designs for 2 meters (short of
multi-element designs) are actually a little poorer than a dipole except
they solve that problem of the feedline coming off at an inconvenient place.
Since on FM you want a vertical antenna, a dipole is messy because you
usually want the antenna up high so you want the feedline to come up from
the bottom. In your case, where you can't get very much height, it may not
be much of a problem to bring the feedline out horizontally for a ways.

Now on 2 meters, height is everything. The J-pole Adrian mentions might
give you the opportunity to get a little more height, which will make it
work a lot better. The J-pole has the feedline coming in at the bottom,
just what you want. Although it is mechanically relatively simple to build,
some people report that it is very tricky to build right. Others seems to
make almost any approximation work well. If you can gain a little more
height by building a J-pole, then I would suggest you go ahead and try it.
There are all sorts of designs out there, and they are pretty inexpensive to
build. But if you are stuck with something close to your window, then then
dipole maybe a better deal.

...

I built a portable 2m J-Pole out of 3/4" copper pipe.

When I want to play on 2m I just drag it out of the garage, and jam it in
the ground. It's less than 10 feet tall, yet with it and my FT2600 at half
power (25w-30w) I have had QSO's with hams on repeater systems almost 100
miles away. I turn the power all the way down to a few watts when working
local repeater systems too.

Go he http://archimedes.galilei.com/raiar/cactus.html

You don't say you're building this for UHF/VHF, so I am making an
assumption.

A great vertical for 15-40m can be found on the W2IK website. And it is
portable.

http://members.aol.com/realhamradio2/W2IK-ANTENNA.html

73 de KB9BVN



"WolfMan" wrote in message
t...
I'm Limited To An Antenna On The Front Of My House. Out My Window I Made A
Simple !/4 wave Verticle Dipole. Would A 1/2 Wave Simply Be Twice The
Length, Using 462/f Mhz, And Would There Be An Advantage With A 1/2 Wave
Over a 1/4 Wave ?
Thanks