[TowerTalk] BIG WIRE BEAMS FOR 75 METERS

[Rick Karlquist]

Joe Subich, W4TV wrote:
>
>  > 3.  Yagi's need to be a half wave high to really play,
>  > but they may still hear OK at a lower height.
>
> The crossover point between a dipole and vertical is actually
> about 0.4 wavelength.  A Yagi will have a slight advantage over
> a dipole because of the slightly reduced (ca. 3 dB) radiation
> up/down.
>
>  > 4.  Verticals with a good ground system are as good
>  > as Yagi's for transmit depending on your ground conductivity.
>  > Fortuitously, I have very high ground conductivity, but
>  > of course YMMV.
>
> Verticals suffer an automatic 6 dB penalty because of the lack
> of ground gain.  Yes, a vertical does very well in the ground-
> wave region - better than any high dipole/yagi.  However, once
> the dipole/yagi is above 0.4/0.35 wave (100 feet/30 meters) the
> horizontal antenna has better radiation at all take-off angles
> in its "forward" direction than the vertical (vs. dipole) or
> 4 square/vertical beam (vs. yagi).
>
> 73,
>
>     ... Joe, W4TV

At least at my QTH, for transmit purposes, a 75m dipole at 130
feet is equal to a 1/4 wave ground mounted vertical for DX.  At lower
heights, the vertical is better.  This is by comparing real
signals on the air.   YMMV.

Rick N6RK