"Richard Harrison" wrote
Richard Fry wrote:
"Was the 0.05 lambda the pitch of the helix? If so, how many turns?"

I`ll quote Bill Orr for accuracy:
etc

Thanks. Maybe I'll model that in NEC and see what it shows. Or did you do
that already?

While the axial-mode helix is a broad-band antenna, the normal-mode
helix is a high-Q antenna and has restricted bandwidth.

The VSWR bandwidth of a normal-mode helix depends on its design. Below is a
link to one that, with branch feed, has a bandwidth of 12 MHz in the FM
broadcast band (see the text at the bottom of the first column of p 1).

http://www.dielectric.com/broadcast/brochures/DCR-M.pdf

Terman is my source for directive gain. On page 871
of his 1955 edition of "Electronic and Radio Engineering" he gives the
directive gain, not in decibles, of 1.5 for the directive gain of the
elementary doublet. It is not isotropic. It is however infinitesimally
short. In the same Table 23-1, Terman gives the gain of the full
half-wave dipole as 1.64.

The 1.5 and 1.64 are multipliers. Multiplying power by 1.64X is a gain of
2.15dBi, that is, 10*log(1.64).

RF