[TowerTalk] Looking for a Short Rotatable Dipole or...

[jimlux]

On 4/28/16 9:31 AM, john at kk9a.com wrote:
> Unless your roof is very high, a rotatable dipole will have little
> directivity. The simplest and least expensive antenna is a wire dipole. If
> you want something better try a 33' vertical with a good ground system.
>

or two dipoles roughly crossing, and a switch or goniometer to select 
between them.

  Dipoles (short dipoles in particular) do not have a "narrow" beam in 
any sense of the word (HPBW is 120 degrees).  What they have is a null 
that can be placed on an interfering signal.

The null *is* fairly narrow

at about 9-10 dB down, it's about 45-50 degrees wide
at 20 dB down it's about 15 degrees wide

So if you want to knock down that big gun in the next city (who you're 
hearing from the sidelobes) so you can hear the other folks you're both 
trying to work, a rotatable dipole (or the electronic equivalent) would 
be useful.




> John KK9A
>
> I''m looking for a 40m rotatable dipole (preferably a F12 EF-140S) to add
> to the C3-SS on my roof.
> The "S"is shortened version. Sadly, nothing larger will fit.
>