[TowerTalk] Fw: Why radials improve radiation!

[Rik van Riel]

On 05/23/2011 11:55 AM, Al Williams wrote:

> 1. However the radiation resistance is a make-believe or psuedo resistance apparently derived from calculations of subtracting ground system power (system loop current x ground resistance)    from the transceiver power output. Thus, since the loop current is known and the remaining power is known, then the radiation resistance can be calculated?
>
> But his seems analagous to lifting oneself up by pulling up on ones bootsraps!

You can calculate this the other way around.

First, build an antenna (say 1/4 wave vertical) with an
exceedingly good ground system (say 120 1/2 wave radials).

Assume that system has near zero ground resistance, and
measure the antenna impedance.

Use that number as the radiation resistance of the antenna.

Now build that same antenna over poor ground (say my back
yard, with 16 1/8 wave radials).  Now measure the antenna
impedance.

Subtract the "good ground" measured impedance from the
antenna impedance measured on the back yard antenna.

The difference is the ground resistance.

> 3. If 2c is true then "heating up the ground comments" hides what is really happening?

If the energy disappears into your antenna system and is
not radiated as RF, it has to go somewhere else.

That somewhere else will almost certainly show up as heat.
I'm willing to bet you a drink of your choice that "heating
up the ground" actually happens :)

(Hey, we might run into each other at a hamfest some day)

-- 
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