Herold beverage discovered in 20 that an otherwise nearly
bidirectional long wire antenna becomes uni-directional by placing it close to
the lossy earth and by terminating one end of the wire with a non-inductive
resistor with a resistance approximately matched to the characteristics or
surge impedance of the antenna. This was the fundamental discovery in his 1921
patent. From the transmission line theory we know that the line
terminated with load impedance equal to characteristic impedance (Z๐),
there is only a traveling wave present on the line. Since there is no
reflected wave, there is no standing wave on the line. Then the line is said to
be non resonant.
It consists of a wire one or two wavelength long. Note that
the length of 1 or 2λ is not a small length at LF or MF; it is hundreds of feet
at MF to several kilometers for LF. The wire runs parallel to the earth’s
surface from the receiver towards the direction of the desired signal. The wire
is suspended by insulated supports approximately two meters above the ground. A
non-inductive resistor of value equal to characteristic impedance is installed
from the far end of the wire to the ground. As the wire is properly terminated,
the structure becomes a non resonant antenna.
