On Mar 29, 5:35*pm, "Richard Fry" wrote:
Quoting from Antenna Engineering Handbook, 2nd Edition by Johnson and Jasik,
page 13-18: "For a normal-mode helix whose dimensions are small compared to
a wavelength, the current distribution along the helix is approximately
sinusoidal."

But John, a helix that is 180 degrees long electrically is not small.
It is electrically double the size of a 1/4WL monopole.

Therefore it is unclear as to the source of
this belief that current would be maximum at the center of "1/2-WL" helix
whose end-end length is 1/4-WL. *In reality the current maximum would be at
the base of the radiator, just as it is for a 1/4-wave linear monopole.

Not true. Any monopole that is electrically 180 degrees long will have
the current maximum point in the middle and a normal mode helix is no
exception. You can easily model such with EZNEC. For any 180 degree
antenna, at the feedpoint, the reflected voltage will arrive in phase
with the forward voltage. The reflected current will arrive 180
degrees out of phase with the forward current.

Zfp = (Vfor+Vref)/(Ifor-Iref) is a current minimum

Take your NEC helical model and adjust the frequency to approximately
double the resonant frequency and take a look at the current
distribution.
--
73, Cecil, w5dxp.com