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
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