Telamon wrote:
The "di" in Dipole means two as in elements. A dipole has two 1/4 wave
elements where a passing EM wave induces an opposing voltage or
potential at its output terminals where the two elements meet.

The way an random wire works with a output terminal on one end of a (1)
wire element is that it has to work against a counter poise or ground.
As such the best potential at its output terminal is when it is a 1/4
wave electrically to a passing EM wave where the dipole would be
electrically at 1/2 wave.

Now that you understand this you can understand that 1/2 wave random
wire is a waste of time and that a end-fed dipole random wire makes no
sense. Yes you can find it out there on the web. Plenty of confused
people in the world.

--
Telamon
Ventura, California

Let us take a look at the 2M 1/4 vertical on my car roof.
It is end fed, and while it is only half of the antenna, the metal
roof is the other "half".

A vertical HF antenna can be built with, dah, a vertical electrical 1/4
wave over
either very conductive, think salt water marsh, or an array of raidals.
The more the
better up to around 190 or so, Contrary to popular ham myth 16 radials
is barely
enough. 32 is better with 64 and moer starting to get there.

Of course it is posible to cheat and use an antenna tuner or "match
box" and
load nearly anthing. Of course just because you managed to get a 1.5:1
doesn't mean
you RF is really going anywhere.

For field day, an anual event held every June where hams take to the
field and pretend
it is an emregency and operate from improvised (and other) antennas. I
used to be
very active with 80M and 40M CW QRP and found out real fast that end
fed dipoles,
or end fed anythings worked much worse then true dipoles.

However I did operate with a 20M 1/4 wave vertical mounted on a large
metal roof that
was simply killer.

An end fed horizontal single side of a dipole will be, generally, way
less effecient
then a true dipole. By runing a counterpoise below the half of the
dipole can, but not
always, improve performance.

And unless one is only interested in receiving one frequency, located
in one direction,
such as WWV on say 10MHz, any sort of dipole is very likely to be way
less then
ideal for general SWL work. In my life I have installed several
dedicated WWV, WWVB systems, this was befroe GPS became as common and
cheap as it now is, and while
logic suggested a dipole would have been a good idea, the fact that I
was trying to
receive 2.5, 5, 10, 15, and once 20MHz meant a dipole's pattern would
fragment,
for lack of a more discriptive word. To do the job right required
mulitple dipoles,
and I found there was no easy way to combine dipoles without the
varrious odd patterns combining for some really odd peaks and nulls.
this required switches to choose between the 4 dipoles and 4 feedlines.
In the last situaiton I ended up going with an active (single ended)
antenna. If I had to do it again I would almost certainly go with a
active dipole.
Other SWLs have found loops to be an effective choice.

I think every new SWL gets hung up on dipoles, failing to grasp that
for 99% of their
listening, dipoles would not be a good choice. Think about it. A
dipoles best stength
is it biggest weakness. The built in peak and null. Peak broadside to
the dipole,
null off the ends. But how do you rotate a true 80M dipole? So do you
errect one for each
target station? That peak in one direction will be a null in another
and just as likely to
be a null for the direction you want as a peak. In my situation I jump
from frequency to
frequency, And the targets wil be at nearly all points of the compass.
Very hard to
build a steerable, broad band dipole. A horizontal active dipole can be
rotated, or a
pair of vertical dipoles can be combined in a Phaser to create an
synthetic rotatable
antenna that gives the ability to peak and null. But we are getting
very complex here,
and quite a leap from any "reasonable" antenna. While quite a leap, it
is what I plan
to have completed by Thanksgiving.

The average SWL will be well served with an antenna like the one DxAce
uses.

http://www.iserv.net/~n8kdv/pics.htm

Simple, inexpensive and will last for years. As their skill sets and
needs evolve, then
it would be reasonable to ponder more complex antenna. It is way too
easy to get lost
in searching for the "perfect" antenna before gaining enough experience
to understand
why perfection isn't needed.

Terry