On Jul 1, 3:18*pm, Roy Lewallen wrote:
Guess I just don't understand how a resonant, helically-wound antenna is
"electrically short". Suppose you helically wound an eighth-wave
vertical in such a way that it was resonant. Its physical length is an
eighth wavelength. What would its "electrical length" be?

Its overall height in free space wavelengths. This is the definition
used by the FCC for the unloaded monopoles used in AM broadcasting

Do you expect your 1/8 WL high, self-resonant helical to have the same
electrical length and feedpoint parameters as a self-resonant,
straight radiator about 1/4 wave high in free space wavelengths?

According to Kraus and other authors, your example above still has
about the same radiation resistance as a 1/8 WL straight conductor --
not that of a self-resonant, straight conductor about 1/4 WL high.

An 1/8 WL high helical may be resonant, but it will not perform the
same in a practical antenna system as a straight, self-resonant
vertical whose physical height in free space wavelengths is about 1/4
wave.

RF