[Antennas] End-fed half-wave religion

[Dan Martin]

Regarding the classic 1/2 wavelength Zepp end fed with a quarter wavelength
open wire (or ladder) line, I felt a lot better about the ol' "how can you
have one end of your feed line not connected to anything" by considering
this:

Stop thinking of it as a 1/2 wave fed with a 1/4 wave parallel line with one
end of your transmission line "unconnected"! That "unconnected" feed line is
the end of your antenna! Think of it for what it is - a one wavelength
antenna that you're feeding at the 3/4 wavelength point. And, oh yeah, that
last 1/4 wavelength wire is tightly folded back against a 1/4 wavelength
section of the 3/4 wavelength part, meaning the last 1/2 wave of your
antenna wire radiates very, very little and the first 1/2 wave radiates the
most.

Considering this concept neatly (and properly) explains a couple of
operational characteristics of the "end fed" Zepp:

1. It explains how you can feed an antenna at an extremely high voltage,
high impedance point. Well, looked at from an overall standpoint, you're
not! You're feeding an antenna >system< at a reasonably low impedance 3/4
wavelength point where a modest matching network works fine. We usually
think of the 1/4 wave feedline as a matching transformer, which it is, of
course, but it's equally valid to look at it as simply feeding a 1
wavelength antenna at an impedance-reasonable 3/4 wavelength point, if that
helps your understanding.
2. It explains how the 1/4 wavelength ladder line radiates little. That's
what happens when you fold a 1/2 wavelength antenna wire back on itself.

Good discussion!

Dan
WB4GRA

> One may argue that an antenna feedline must in all cases be attached
> to "something" on both sides, using the "complete circuit" argument.
>
> On some level, it is difficult to successfully argue that the other
> side of the feed mechanism *must* be connected to something else,
> because, hey... lots and lots of people are using antenna systems
> in which there is no such connection, and many of them are well
> experienced and educated amateurs who are very happy with the
> performance of their antenna systems.  It's really hard to dismiss
> them all as a bunch of dimwits who little realize that once in a
> while, one can even make contacts on a dummy load.