[TowerTalk] Fwd: Re: vertical ground experiment

[Rick Karlquist]

The 36 ohm number is for a infinitesimally thin vertical that
is 1/4 wave high as measured in free space wavelengths
(and hence will be somewhat off resonance).

Fat verticals have considerably lower driving point impedance
at 1/4 wave and furthermore, have to be shortened more to achieve
resonance, so the impedance at resonance is reduced even more.
If the vertical is tapered or has top loading, things get even stranger.

Rick N6RK


John Cowan wrote:
> That was in reference to:
>
>   "A 1/4 wave vertical over perfect ground should measure about 36 ohms
> of pure resistance at the feed point. Any loss in the ground will be
> added to the 36 ohms and can be easily measured.
>
> If for example, you measure 50 ohms you might think you have an
> excellent match, and you do, but you have about 14 ohms of resistance
> in series with the ground plane. Not good. "
>
>   I keep reading about this "perfect ground of 36 Ohms". I was trying to
> figure out how having less than 36 Ohms is significant, insignificant,
> or just an ambiguous reading.
>
> Dan Zimmerman N3OX <n3ox at n3ox.net> wrote:
>   That the feedpoint impedance is 27 ohms.
>
> On 6/21/07, John Cowan wrote:
>> If I have a 1/4 wave vertical and the feedpoint measures 27 ohms, what
>> does that tell me?
>>
>> Note: forwarded message attached.
>>
>> John W0TMM
>>
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