This is my forum for telling the world
what's
keeping me busy these days.
The zepp antenna, so named because it was used on zeppelins. It's an
end-fed half wave.
In this picture we've taken the 3/4 wave vertical
and made a 90 degree kink in it, showing what's actually happening.
It's a half wave wire (or pipe) fed with a shorted quarter wave
transmission line. With the short at the bottom, the top is
theoretically infinite impedance. With a correct length wire the
number becomes real (between 1500 and 5000 ohms) and can be matched to
50 ohms, using the parallel line as a transformer. Since it is a
transmission line, it doesn't have to be any particular spacing, or
even a spaced line at all. I made one for experimental purposes using
direct-burial CATV wire somewhere between RG-6 and RG-11 in size for
both the transformer and the radiator. It seemed to work OK, though I
imagine that I was losing some signal in the 100 to 1 SWR at the tippy
top of the transformer. I also built one using twin-lead, and I will be
trying #14 bare copper with a plastic frame to space the transformer
wires, and an inline one using speaker wire.
| Previous
page |
Next page |
Questions?
Comments? Email me - jim (at) jimdaldry.com