On Tue, 25 Apr 2017 17:24:37 -0700, (Dave
Platt) wrote:

My mental model of the alternating-sections design has been that all
of the sections do radiate... the alternating hookup forces them to
radiate in phase with one another, rather than out of phase (and thus
tending to squint the pattern badly upwards and downwards).

Sheesh. I'm an idiot. I just noticed that I already have a model of
an alternating coax collinear on my own web pile:
http://802.11junk.com/jeffl/antennas/CoaxVert/index.html
It's not my design. I vaguely recall asking some questions about this
antenna, and someone sent it to me. Notice in the Geometry that every
other 1/2 wave elements do the radiating. The comments are useful:

CM Coaxial Vertical Antenna, converted with 4nec2 on 28-Nov-08 22:18
CM This "Franklin" array model was created by Linley Gumm,
CM K7HFD. Coaxial cable is modeled as a combination of
CM transmission line model, to represent the inside of the
CM coax, and a wire to represent the outside. The technique is
CM described in the EZNEC manual. See "Coaxial Cable,
CM Modeling" in the index.

Notice that if you replace the non-radiating 1/2 wave coax delay line
sections with a 1/4 wave wire stubs (or end shorted ladder line), the
antenna is now about half its previous length, with no loss in gain,
and probably little change in pattern.

Also:
https://ukradioscanning.com/viewtopic.php?f=5&t=3028
Note that the drawing shows that all elements radiation, but the
nearby comments say "(on outer conductor for radiation)" which means
that only those segments that have exposed outer shield conductors
connected to the feed coax center conductor, do the radiating. That's
every other 1/2 wave segment.




--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558