[TowerTalk] 75 meter antenna

[Jim Lux]

At 09:02 AM 4/7/2005, Al Williams wrote:
>EZNEC shows that this configuration is a barn burner for straight up
>propagation providing about 4 db gain over a single dipole and much
>attenuation at lower elevation angles.  However EZNEC shows that raising the
>antennas from 15' to 20/25 adds about 1 db of gain.  NVIS articles and 1
>book that I have read say
>that the optimum height is about .2 lambda which agrees with my EZNEC
>modeling. Raising the antennas also makes the input impedance a bit more
>manageable.
>EZNEC doesn't seem to agree with the "...theoretical gain of about 7db"  as
>it reports about 10 dbi?
>
>It would seem that this configuration would be especially helpful in areas
>with high ham populations--not so good in Wyoming, etc.
>
>k7puc

A lot of the details are going to depend on what the soil properties are, 
and I'd venture that most hams don't have a real good handle on exactly 
what they are for their particular site.

When you ran your EZNEC models did you use the sommerfield ground or the 
reflection coefficient? (makes a big difference on feed point impedances, 
and the corresponding gains)