Sorry, I take issue with this. The radiation resistance, as universally
used in the professional literature, *is* a distributed radiation
resistance -- it's the resistance that "consumes" the power radiated
from the entire antenna, not just one point on the antenna. But that
entire power-consuming property is commonly lumped into a single
component -- the "radiation resistance" which can be defined (or
"referred to") anywhere on the antenna you'd like, including but not
limited to the feedpoint. And when placed at that point, it consumes the
amount of power radiated from the entire antenna. It's not one single,
absolute value, but a component whose value depends on where you define
it on the antenna. A very simple and correct way of looking at it is to
realize that if P watts is being radiated from the antenna, the
radiation resistance value has to equal P/I^2, where I is the magnitude
of the current at the point where you're measuring or defining the
radiation resistance. So the radiation resistance always "consumes" P watts.

If you want to calculate efficiency, you have to do the same thing with
the loss resistance, and make a single R that consumes the same amount
of power as the total antenna loss. Again, you can define it anywhere on
the antenna including the feedpoint, and it'll have a different value
wherever you put it. To calculate efficiency from radiation and loss
resistances, both have to be -- correctly -- defined at (or "referred
to") the same point.

There's no need for additional "essential" fundamental terms -- the
simple concept of radiation resistance as I've described it is perfectly
adequate to explain and calculate antenna radiation and efficiency. But
like other concepts, it does take a little effort to understand it.

Roy Lewallen, W7EL

Reg Edwards wrote:

Radiation Resistance.

Roy, what an excellent, well needed exposition, in plain English, addressed
mainly to professionals who should know better, and are guilty (dare I say
it) of obtaining money under false pretences.

You omitted only "DISTRIBUTED radiation resistance", a term essential to but
absent from this newsgroup. It's probably also absent from Terman and Kraus,
the latter I have never read. It's an aid to clear logical thought.

It should be used whenever radiation resistance is compared with conductor
resistance, inductance, capacitance, etc., of elongated wires and loading
coils.

As an example, it so happens that the distributed, end-to-end, radiation
resistance, Rd, of a half-wave diopole is exactly twice (easily proved) the
feedpoint resistance of around 72 ohms.

The radiating efficiency of a half-wave dipole is then, very simply and
accurately -

Efficiency = 144 / ( 144 + overall HF conductor resistance )

although some old-wives may wish to argue about it on the grounds that it's
far too simple.
----
Reg, G4FGQ