[Antennas] Would vertical be better than yagi?

2002年6月13日 07:23:24 -0400

Karl and All,
Where in the literature is this addressed? I researched Moxon, ARRL, Orr,=
=20
ON4UN and others, and they all start with a 1/2 wavelength height. Orr=20
comes closest to it, but it's still for antennas at 1/2 wave length and=20
higher heights. Good field for investigation. "Advantages of Beam Antennas=
=20
for Field Day Use." Not I, thank you.
At 05:26 AM 6/13/2002 -0400, you wrote:
>W1CG wrote:
>> > I always thought the Yagi had a lower angle of radiation than a dipole=
=20
> when
> > both antenna were at very low heights.
>>AA4NU wrote:
>> > Charles is correct, his models are pretty much on the mark. What he has
> > done is to remind us of the impact of using a directional array, as in
> > either a parasitic, or driven array at lower heights may, due to the=20
> pattern
> > being changed, actually lower the average angle of radiation ...
>>>Thanks for the .EZ files, Chas. I was really able to verify your results=
 and
>both of you are absolutely right: The addition of parasitic or driven
>elements indeed lowers the the radiation angle of an antenna and the lower
>the height above ground the more pronounced is this effect. Obviously, at=
 low
>heights it is not permissible to consider the antenna to be a point-source=
 of
>radiation and I assume that the lowering of radiation angle increases with
>element spacing. I compared a Dipole and 3el.-Yagi on 14 MHz at different
>heights above average ground (conductivity 5 mS, dielectric constant 13,=
 high
>accuracy ground model) with EzNEC 3.0, here are the results for max. lobe
>gain and elevation angle:
>>@ 5m (Lambda/4): Dipole 5.8 dBi @ 69=B0 / Yagi 9.8 dBi @ 39=B0
>@ 10m (Lambda/2): Dipole 7.1 dBi @ 30=B0 / Yagi 12.2 dBi @ 26=B0
>@ 20m (Lambda): Dipole 7.4 dBi @ 15=B0 / Yagi 13.4 dBi @ 14=B0
>>The results clearly support your point. Interesting discussion - This is a
>new and very valuable finding for me, thank you !
>>73
>Karl, DJ5IL

73, Chas, W1CG