What might be of interest in this discussion is that after he derives the
impedance of free space, he uses that to find the Radiation Resistance of a
short dipole for dW. Where d is the length of the dipole and W is
wavelength. (I did not want to do Greek letters). He ends up with an
equation of the form

R=377k(d/W)**2 or R=790 (d/W)**2.

As a sanity check let d/W=1/2, which violates the , but still gives a
fairly close answer of 197 Ohms, compared to the actual 168 Ohms. Note that
this is not the same as Feedpoint Resistance because it is not referred to
the current maximum. Kraus does not actually say this, but seems that the
near field would be the mechanism for "matching" this to the far field 377
Ohms. The transmitter only sees the feedpoint, the rest of the universe sees
the whole antenna.

If I interpret it correctly, this 197 (168) Ohms in independent of where you
feed the dipole. Kind of hard to boil several pages into one paragraph,
especially since most of this stuff I haven't seen in decades.

Tam/WB2TT
"Dr. Slick" wrote in message
om...

I don't have that book. What does it say?


Slick

Dr. Slick wrote:
"What does it say?"

I don`t have Kraus, unfortunately.

I do have Arnold B. Bailey`s "TV and Other Receiving Antennas". Bailey
covers more antenna territory than most, and does an excellent job of
it. Bailey also includes a catalog of antenna types, all sized for 200
MHz for easy comparison.

Bailey says the surge impedance of an antenna is inversely proportional
to the capacitance per unit length. Reminds one of a transmission line.
This is non-uniform, so Bailey has an empirical equation which says the
larger the periphery of the rod, ther smaller the average surge
impedance.

The ratio of the electric field to the magnetic field surrounding an
antenna must be related to the ratio of volts to amps in the antenna
wire (the surge impedance).

The surge impedance of a thin-wire 1/2-wave dipole from page 500 is 610
ohms (average).

The surge impedance of a fat-cylinder 1/2-wave dipole from page 502 is
240 ohms (average).

Pattern and gain are identical for both antennas. But, Dr. Slick may be
on to something after all. The bandwidth of the fat antenna is about 3X
that that of the thin. In antennas, bandwidth is often an indicator of
match.

Best regards, Richard Harrison, KB5WZI