[TowerTalk] Cage dipole revisited.

[Joe Subich, W4TV]

> > Dan Zimmerman N3OX wrote:
> >   
> >> There was possibly an implication in my post that **any
> >> such claim** was a **lie**, and that I had some specific 
> >> knowledge that a factual mis-statement must be taking 
> >> place if such a statement is made.

Put simply, for such claim to be valid the feed impedance 
of the cage dipole would need to be substantially less than 
50 Ohms such that the total current flowing in the cage 
elements was approximately 3.16 times the current flowing 
in the single element dipole.  For an antenna to show gain 
the product of current and length must increase ... e.g., 
the same current in a larger area or more current in the 
same area.  Since the cage dipole is shorter than a normal 
half wave dipole (L/D ratio), the only way it can show gain 
is through an increased current.  

Note there is no "current times number of wires" advantage 
for the cage dipole because the current in the element is  
divided (equally) among he number of wires in the cage.  The 
only gain is a slight increase in antenna efficiency due to 
decrease in I^2 * R losses  (the resistive losses in a five 
wire cage would be only 20% of those in a single wire dipole 
using the same wire).  However, since the resistive losses 
in copper or aluminum antenna elements is exceedingly small, 
the increase in efficiency represents only a small fraction 
of a dB in antenna "gain" and is dwarfed by environmental 
factors.   

All of this is basic electromagnetics and is discussed 
fully by Kraus and others in the standard antenna texts. 

73, 

   ... Joe, W4TV