Telamon wrote:
In article ,
John Doty wrote:


Frank Dresser wrote:


I recognized Telemon's antenna formula as something very much like
the transmission line formula. I'm not sure how it applies to
resonant receiving/transmitting end fed wires. If it does, I'd
like to learn something.

For a wire antenna, the field configuration near the wire is very
similar to the field inside a coaxial cable. Unsurprisingly, it has
similar behavior: the bulk of the energy tends to propagate along the
wire and not radiate. This leads to Schelkunoff's approximation: you
calculate the current distribution along the antenna as if it was a
transmission line, and then calculate the radiation due to that
current distribution. You can get the antenna impedance by
calculating the impedance of a lossy transmission line (with loss
equal to the radiation) with the assumed current distribution. You
get the reception properties by reciprocity.


It boils down to this, smaller RF current loops radiate less
effectively.

Yes, but what does that have to do with the discussion above?

The wire will become a better antenna the higher it is off
the ground.

Often true. Nevertheless, a low Beverage can be an extremely effective
antenna.


If the wire was vertical instead of horizontal then it would not look
like transmission line where the inductance and capacitance are evenly
distributed over its length.


Actually, the Schelkunoff approximation works quite well in that case.
The field near the wire is not strongly affected by its orientation. The
characteristic impedance varies only logarithmically with distance from
ground, so that except for a modest bump in the immediate vicinity of
ground, the inductance and capacitance per unit length are nearly
constant. If this was not true, the Schelkunoff approximation would be
nearly useless.

-jpd