Practical_Antenna_Handbook_0071639586

358 p a r t V : h i g h - F r e q u e n c y A n t e n n a s f o r S p e c i a l i z e d U s e s
Figure 14.18 Coaxial-cable shielded loop.
The EWE Antenna
In 1995 Floyd Koonce, WA2VWL, published details of his EWE antenna, which provides
MF and low HF receiving directivity in a much smaller footprint than a Beverage
antenna. The acronym EWE is not only descriptive (Earth-Wire-Earth) but a play on
words, as well, since the antenna has the shape of an inverted “U” (in response to which
the author can only say “Bah!”).
The EWE of Fig. 14.19 functions much as if it were a two-element phased array of
short verticals. However, like the Beverage, the EWE is a traveling wave antenna. Directivity
is a result of phase and amplitude differences between the two vertical segments;
these differences, in turn, originate in the length of the horizontal wire connecting the
vertical runs, the value of the termination resistor, and the fact that a current flowing
upward in one vertical segment flows downward in the other.
Unlike the Beverage, the EWE receives from the end of the antenna opposite the termination
resistor. Because the antenna is not a resonant device, it is relatively broadband
in operation, although the optimum value of termination resistance varies with
frequency (and with the exact characteristics of the ground beneath the antenna). The
value of the termination is best set by tuning for a null off the back of the antenna by
listening to appropriate stations in the AM broadcast band or on 160 m. Typical values
for the termination resistor are in the 700- to 900-Ω range. The input impedance is somewhat
lower and is a reasonably
Incoming
signal
10-15'
40-50'
10-15'
good match to 50-Ω coax and receiver
inputs via a 9:1 transformer.
Although the EWE requires a
much smaller space than a Beverage
antenna, to achieve its full po-
To
Receiver
1:3
700-1400
Figure 14.19 EWE antenna.