Jim Kelley wrote:
"I don`t quite grasp the purpose of your bolt comparison, Richard."

My point was that the signal is guided by the wire on the coil and isn`t
instantly transported by induction from one end of the coil to the
other. How long it takes the signal to travel the length of the coil
depends on the length of wire in the coil as well as the velocity factor
of the wave on the wire in the coil. If it were not so, Terman`s
explanation of the traveling wave tube (TWT) would not be valid. But,
GTE Lenkurt gives a similar explanation in its "Demodulator" of the TWT.
They manufactured TWT amplifiers and surely knew how they worked.

A coil is a coil whether it is used in a traveling wave tube or used to
load an antenna. The velocity factors are surely a function of coil
dimensions as illustrated by the research results given by Kraus in
Fig.7-19 in the 1950 edition of "Antennas". The variation surprises me.
There is probably more research which explains such variations.

Best regards, Richard Harrison, KB5WZI