[Antennas] RE: J POLE QUESTION

[Dan Richardson]

At 11:30 AM 7/11/2002 -0400, Sean wrote:
>So, what is the gain of a J-Pole over a vertically polarized dipole?
>Over a 5/8 wave?  I've been thinking about building a J-Pole, but won't
>waste my time if a 5/8 wave is simpler and has more gain?  What are the
>advantages of a J-Pole?

Sean,

As I stated in an earlier post modeling a standard j-pole using NEC the=20
gain (for all practical purposes) is about the same as a =BD-wavelength=
 dipole.

A comment on the 5/8-wavelength monopole. First the gain of 3 dB is=20
referenced to a =BC-wave monopole. Secondly, and more importantly, to have=
=20
the stated 3 dBqw gain the antenna must be mounted directly on a perfect=20
conducting ground that is infinitely flat. If any of those conditions are=20
not met then all bets are off as far as gain goes. Elevating the antenna=20
will not result in the claimed 3 dBqw gain.

If you looking for a good 3 dB gain antenna you might want to consider=20
building a 1=BC-wave dipole (sometimes referred to as a double extended=
 Zepp)=20
mounted vertically. That antenna will have a free space gain of 3 dBd (gain=
=20
over a dipole), has a good omni-directional azimuth pattern which is=20
concentrated towards the horizon.

73
Danny, K6MHE