[Top] [All Lists]

Re: [TowerTalk] trees and verticals

Subject: Re: [TowerTalk] trees and verticals
From: David Gilbert <>
Date: Wed, 28 Dec 2011 11:42:14 -0700
List-post: <">>

How much current gets induced in an element made from any material is a 
function of it's physical shape, material properties (conductivity, 
dielectric constant, etc), proximity and orientation relative to the 
originating RF, etc.  The magnitude of that current can range from 
negligible to appreciable.

How much of that current gets re-radiated or converted to heat is a 
function of the loss characteristics of the material.  That loss can 
range from essentially zero to very high.

Your three bullets describe the resulting range of possibilities.

Dave   AB7E

On 12/28/2011 9:36 AM, Rik van Riel wrote:
> On 12/27/2011 04:30 PM, David Gilbert wrote:
>> Fundamentally, when RF hits a conducting element (wire, piece of tubing,
>> tree, side of a building, etc) it induces currents in that element ...
>> currents that are no different than if you had been able to somehow
>> connect your transmit coax to it.  Those currents generate an
>> electromagnetic field around that element that is in fact re-radiated
>> RF.  If the element is lossy (wood, dirt, wet mattress, etc) the induced
>> currents are dissipated as heat instead of being re-radiated.
> I think I get it now...
> 1) If the element is very low resistance, the RF will
>      induce a lot of current, but it will get re-radiated.
> 2) If the element is medium low resistance, the RF
>      will induce a fair amount of current, but it will
>      get absorbed.
> 3) If the element is very high resistance, the RF
>      will induce very little current. You do not care
>      that it is absorbed, because it is so little.
> Is this a fair synopsis?

TowerTalk mailing list

<Prev in Thread] Current Thread [Next in Thread>