On Thu, 2 Feb 2006 20:57:23 +0100, "Meindert Sprang"
wrote:

"Bruce in Alaska" wrote in message
...
In article ,
"Meindert Sprang" wrote:

These antennas are half-wave antennas and they don't need a
counterpoise.
Only a quarter-wave antenna needs one, to account for the other missing
quarterwave part, so to speak.

Meindert

Well, that is not actually true in most cases.

I see. My Shakespear is a 1/2 wave whip with a coil in the base.

If you actually take a
Shakespear Fiberglass VHF Antenna apart, you will find that they are
1/4 wave driven elements, with 1/4 wave of Ground Sleeve shoved up
the inside of a hollow fiberglass fishing pole and epoxed in place.

But doesn't this ground sleeve produce the "other end" of the dipole?

Meindert


Yes that's true the sleeve is the other end of the dipole. The
difference is with the sleeve the antenna is essentially center fed
just like a dipole or a ground plane. In the case of the sleeve if you
picture a ground plane antenna with radials but instead of the radials
sticking out you fold them down over the coax in the form of a sleeve.

With an end fed ½ wave like some antennas are (metz is one) the coil
is at the bottom but it still requires some counterpoise. In that case
the outer shield of the coax serves as such.
Being a high impedance feed the ground currents are very low so it
doesn't take much of a ground for them to work rather well.

The collinear gain type antennas, as Bruce says, have stacked elements
starting at the bottom with the sleeve antenna. Often the stacked
elements are nothing more than quarter wave lengths of coax with the
center conductor and shield swapped on each section. Very cheap to
make.

Regards
Gary