On Sun, 01 Apr 2007 18:24:33 GMT, Cecil Moore wrote:

AndyS wrote:
Not to make too fine a point on this, Cec, but I , personally,
would consider a perfect 52 ohm antenna to be a dissipationless
resistor......... although, in the cosmic sense, the power that is
fed into it will eventually reside as "heat" in the bowels of the
cosmos.....somewhere......

Yep, a common misconception. The feedpoint impedance
of a standing-wave antenna, like a 1/2WL dipole, is
a *virtual* impedance equal to (Vfor+Vref)/(Ifor+Iref).
It may be a resistance, but it is not a resistor. It
is essentially the same entity as the impedance looking
into a stub. For a resonant 1/2WL dipole the equation
becomes:

Feedpoint resistance = (|Vfor|-|Vref|)/(|Ifor|+|Iref|)

With Vfor at a reference angle of zero, Vref is at
180 degrees. With Ifor at zero degrees, Iref is
also at zero degrees. Thus the ability to add and
subtract magnitudes directly.

Some guru once challenged me to make a measurement
at the shack and tell the difference between a 50 ohm
dipole and a 50 ohm resistor. Told him all I needed
was a field strength meter. :-)

The words "impedor" and "resistor" are reserved for
real physical devices. The words "impedance" and
"resistance" have two meanings and can mean either
real devices or virtual V/I's. So says the IEEE
Dictionary.


Amen to that, Cecil

Walt, W2DU