[TowerTalk] Balanced Line using Coax ?

[Chuck Counselman]

At 9:34 AM -0700 7/29/03, Jim Lux wrote:
>...Looking at loss as a dB/foot for the coax, you divide the power 
>into two pieces of coax, so the absolute loss (in watts) will be 
>half in each piece of coax, but you've got two coaxes, so the total 
>loss is exactly the same....


No.  To deliver the _same_power_ as a single coaxial line, two 
coaxial lines operating in "push-pull" deliver half the current at 
twice the voltage.  At HF, virtually all of the loss is ohmic, and 
the power dissipated per unit length of conductor is equal to I^2*R', 
where I is the current in the conductor, I^2 is I squared, and R' is 
the resistance per unit length of conductor.  With half the current, 
the power dissipated per unit length of conductor is quartered; the 
length of conductor is doubled; so the total power dissipated in the 
pair of push-pull coaxial lines is one-half that dissipated in a 
single coaxial line carrying the _same_power_.

-Chuck, W1HIS