Practical_Antenna_Handbook_0071639586

C h a p t e r 1 4 : r e c e i v i n g A n t e n n a s f o r H i g h F r e q u e n c y 339
of weak DX signals on the AM broadcast band or lower-frequency ham bands jump out
of the background noise in your headphones. Yes, the author’s 250-ft Beverages are “too
short” to be of much use on 160 m. Yes, the author’s Beverages should have matching
transformers and isolated grounds. Etcetera, etcetera. But once the three most important
compass headings were determined, each of the author’s Beverages took no more
than two or three hours to install and connect. And they work on 160, 80, 40, and the
AM broadcast band! Could they be fine-tuned to work better? Yep! Do they work well
enough? Yep! Did they cost a lot? Nope! In short, the Beverage is the epitome of a practical
antenna.
The Bidirectional Beverage
With some clever transformer “magic”, two Beverages, consisting of two parallel wires
and capable of receiving from two separate compass headings 180 degrees apart, can
share a common set of supports and a common feedline attached to the end of the wire
pair that is nearer the receiver.
Figure 14.4 shows the circuit configuration that allows switching of the wires and
the feedlines for two opposing directions. The parallel wires can be implemented in a
variety of ways:
• Separate wires about a foot apart, supported by cross-arms atop wood or PVC
supports
• Open-wire transmission line
• Two-conductor jacketed house wiring
• Surplus multiconductor cable
Transformers T 1 and T 2 are designed to transform the Beverage impedance down to
the characteristic impedance, Z 0 , of the coaxial feedline to the receiver. In operation, one
of the two coaxial cables feeds the receiver while the other cable must be terminated in
Z 0 . This can be done at the receiver end, but, alternatively, to avoid running two transmission
lines to the receiver, the resistive load switching and swapping of transformers
feeding the receiver can be performed in a protective enclosure near the end of the Beverage
that is attached to transformer T 1 . In the latter configuration, the dc control signal
T 3
T 1
Secondary Primary
To receiver
or termination
Secondary
T 2
Primary
1 foot
Primary
or less
Secondary
To termination
or receiver
Figure 14.4 Two-wire reversible Beverage.