[Elecraft] EFHW

[Tony Estep]

On Sat, Feb 11, 2017 at 11:19 PM, Kevin - K4VD <kevin at k4vd.net> wrote:

> ...The end fed is only 10% efficient (did I get that right)...

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No, that's not right. The radiation pattern and gain of an end-fed halfwave
are little different from a center-fed dipole. The efficiency of an antenna
is not affected by feedpoint location. The end-fed antenna may be harder to
match than a center-fed, but that's a different question. If you have a
proper matching arrangement between the antenna's high impedance and your
feedline, you'll get results that are essentially identical to a standard
doublet. As I mentioned in an earlier post, two minutes with EZNEC will
clarify this.

"Efficiency" refers to the quotient of the antenna's radiation resistance,
divided by ohmic losses. If you have a short piece of wire, its radiation
resistance will be low, but for a half-wave wire it's 73 ohms, no matter
where it's fed.

As a side-note, I worked over 300 countries with a 100-foot wire strung out
my bedroom window (16 feet above the driveway) and running to a tree at the
end of the yard, 40 feet high at the far end. There's a picture of it on my
qrz.com page.

Tony KT0NY