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Changing the Resonant Frequency
The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher
bands. (The antenna wire could also be tuned for the lower end of 40 meters without the coil but the
resonance on the higher bands will be progressively higher in the bands.)
You can also adjust the resonant frequency by changing the number of turns on the loading coil.
Removing turns will raise the resonant frequency. This requires removing the ring terminal (a new
terminal will be required), pulling the short end of the antenna wire through the coil form holes,
unwinding the desired turns, re-threading the wire through the coil form holes, and reattaching the wire
to the antenna attachment screw (without a terminal). When the desired SWR and frequency are
achieved, attach a new ring terminal and replace the strain relief thimble and wire clip hardware.
The antenna is not designed for a low SWR on the 30, 17, or 12 meter bands but can be used with an
antenna tuner and low-loss coaxial feed line to minimize losses due to the high SWR on those bands.
Installing the Antenna
Figure 2
shows some of the most common ways to install the EFHW. In
Figure 2A
(top), the impedance
transformer unit is supported by a cord or rope and the antenna wire is stretched out horizontally or
sloping toward the ground. (The support eyebolt is not electrically connected to any part of the
antenna.) In Figure 2B (bottom), the impedance transformer unit is at or a small height above ground
level and the antenna wire is elevated at the far end or in the middle. Antenna configuration is
generally not critical but it is helpful to understand feed line interaction and counterpoise function.
In
Figure 2A,
the ground attachment screw of the transformer is not connected and the outer surface of
the coaxial feed line shield becomes part of the antenna, carrying significant common-mode RF current
for at least ¼-wavelength from the transformer. If this causes RFI or other undesired effects, a choke
balun or “line isolator” may be used at a distance from the transformer to reduce the current. Do not
use a choke balun at the transformer unit in this configuration because it will block this current path,
reducing the antenna’s effectiveness
.
