Cecil, W5DXP wrote:
"Anything about dissipationless resistances or negative resistances (in
"Transmission Lines, Antennas, and Wave Guides")?"

On page 73, the characteristic resistance of free-space is defined as
the sq rt of the permeability of space devided by the dielectric
constant of space. The units are henries/m and farads/m. The solution is
a voltage to current ratio of 376.7 ohms, or 120 pi ohms.

As free-space is a perfect (lossless) medium for radio waves, it is a
dissipationless resistance.

On page 13, the characteristic resistance (Ro) of a transmission line is
given in formula (14.3) as the sq rt of L/C, but this is an
approximation for low-loss lines as there are no perfect lines.

Negative resistance is a gain instead of a loss. The authors of
"Transmission Lines, Antennas, and Wave Guides" were writing for WW-2
officers being trained at Harvard University in radio and radar. The
phone system was then using some "negative resistance repeaters" but
neither these nor "active antennas" were big at that time. You can only
make up the loss in a two-wire phone loop with amplification. Any more
gain and the loop "sings" (breaks into oscillation).

Best regards, Richard Harrison, KB5WZI