Re: [TowerTalk] antenna impedence and ground impedence??

[Dan Sawyer <dansawyer@earthlink.net>]

Tom,

I am trying to increase the efficiency of a center loaded vertical by 
creating a good ground system.

Based on models the antenna 'should' have a have a total impedance of 
less then 10 Ohms. Yet it reads close to 50 Ohms. I assume the 40 plus 
Ohms is related to ground resistance. Is this a reasonable starting 
assumption??

Dan

Tom Rauch wrote:

> > Measuring ground resistance is easy. You just have to make a lot of
> > measurements.
> > This is how we find mineral veins which we can map based on the
> > measurements.
> > Any introductory text on geophysical prospecting using potential methods
> > will
> > teach you all you need to know. The math isn't bad.
> >    
>
> It definitely isn't easy.
>
> It is all but impossible for a ham to measure the radiation resistance,
> ground loss resistance, and antenna loss resistances. Even broadcast
> stations are forced to back the data out of many dozens or hundreds of FS
> measurements in a proof of performance. Even with a full proof and careful
> work you are lucky to be within 3dB.
>
> I don't know what you are measuring, but accurately estimating the portion
> of resistances normalized to one point in the system from antenna loss
> resistances, radiation, and ground losses so you can estimate efficiency is
> all but impossible outside of a complex test environment. This is what he
> wanted to do, not to know the DC or low frequency AC soil resistance between
> two or three probes.
>
> With enough measurements we can learn the average low frequency
> characteristics of soil, but that data doesn't mean anything in this
> application. Neither does a meter at the antenna feedpoint.
>
> 73 Tom
>
>  
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