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MANUAL: ENDFEDZ 40-10-KW EFHW 1KW ICAS ANTENNA
The EFHW (End-Fed Half-
Wave) antenna is one of amateur radio’s oldest antenna designs. Originally
known as the “end
-
fed Zepp,” it was used by airships (known as “Zeppelins”)
suspended from the fed
end with the free end hanging loose. The end-fed Zepp was driven with tuned feed line sections,
making it primarily a single-band antenna.
The EFHW performs similarly to a resonant, half-wavelength dipole on 40 meters, radiating best
broadside to the antenna. As long as the impedance at the end of the antenna is suitably high, the SWR
will low enough to be used on the higher HF bands without an antenna tuner. As operating frequency
increases, the pattern develops multiple lobes at angles closer to the line of the antenna. Above and
below the HF bands, transformer losses increase, impedance matching is not guaranteed, and damage
to the transformer may result at higher powers.
The 40-10-KW consists of the two components shown in
Figure 1
–
the antenna wire and an impedance
transformer. Designed to be used on 40, 20, 15, and 10 meters, the EFHW antenna wire is
approximately one half-wavelength long on 40 meters. A 49:1 impedance transformer converts the high
feed point impedance of the wire at its end to a value closer to 50
, more suitable for use with coaxial
feed lines.
Figure 1
–
EFHW Transformer Unit and Antenna Wire
