[Fwd: LF: Vertical versus Inverted-L]

[Andre' Kesteloot]

vernall wrote:

> Peter Dodd wrote:
> >
> > If the results of computer modelling electrically short antennas fed
> > against ground are to be believed, these antennas radiate in an
> > omni-directional manner; with a deep null in elevation. This is true
> > regardless of what shape you make the antenna, be it an inverted L or a T etc.
> > If the antenna is not electrically short, as in the case of Rieno's
> > antenna then  much of the signal is radiated vertically, giving us
> > those interesting propagation effects.
> >
> > However, in spite of what the antenna modelling predicts about short
> > antennas there is a lot of evidence that short vertical antennas used
> > by amateurs do have directional properties. For example G4GVC is
> > about 1 S-point stronger than G3KEV at this location. From what is
> > known about the erp's of the two stations it implies a directional
> > effect, which is probably caused by the ground portion of the
> > radiating system, a factor difficult to model using the existing
> > antenna modelling software.
> >
> > *********Seasons Greetings to all the LF Group**********
> >
> > --
> > Regards, Peter, G3LDO
> >
> > <g3ldo@zetnet.co.uk>
> Modelling I have done also strongly suggests that the type of top
> loading, and whether or not it is "lop sided", does not make much
> difference to the pattern, which is onmidirectional (the overhead null
> or minimum is not of much significance for DX working).
>
> I too have observed what seem to be moderately directional properties,
> but I believe this could be more to do with the surrounding environment
> rather than the antenna wire as such.  Nearby buildings and trees
> distort the electric flux pattern (short verticals are fairly high
> impedance affairs) and the near field distortion takes its toll on what
> the computer model (usually with no nearby objects included) says is
> omnidirectional.
>
> Also at moderate distances the ground conductivity likely varies with
> path, and that too can lead to wrong deductions being made about
> directional antennas, when it is actually differential path loss.
>
> However, an intersting topic ....
>
> Cheers (and beers),
>
> Bob ZL2CA