The Beverage Antenna, 100 Years Later

1 The Beverage Antenna, 100 Years Later Still relevant for its noise-rejection abilities, the Beverage will become more important during Solar Cycle 25 as increasing sunspot activity leads to weaker signals on 160 and 80 meters. Ward Silver, N AX, and The trade-off is length Beverages need to be at least Frank Donovan, W3 LPL 3. 4 long to provide effective noise rejection. On June 7, 1921, Harold Beverage , W2 BML, (previ- ously 2 BML) obtained his first patent for his radio Wave Front Tilt receiving system. Back then, as they do now, operators A radio wave is an electromagnetic field (EMF) with an struggled to hear signals through the atmospheric static electric (E) and magnetic field strength (H) component that grew stronger as the frequency dropped.

2 The VLF- at right angles. An EMF induces voltage and current in through-MF spectrum had very high noise levels that every conductor it encounters. How much voltage and overloaded receivers and made consistent reception current depends on the orientation of the EMF, with very difficult, particularly in the summer months. respect to the antenna. As a radio wave arrives from the ionosphere, its vertically polarized electric field compo- Beverage 's main discovery was that a long horizontal nent (E field) is tilted forward, as shown in Figure 2. wire (known to have a bidirectional pattern) could be Wave front tilt results from being reflected by the iono- made unidirectional by keeping it close to the ground sphere.

3 Higher arrival angles increase the tilt. and terminating one end of the wire with a resistor. When the wire was aimed at the transmitting station, Figure 2 shows why tilt is important. For the wave to this had the effect of rejecting noise and interference induce a voltage in the antenna, the E field must at from other directions, which increased the signal-to- least partially align with the antenna. There won't be noise ratio (SNR). any voltage if the wave front arrives with a perfectly ver- tical E field. When the E field is tilted, however slightly, it A Basic System becomes partially parallel to the antenna. The vertical The basic Beverage antenna system is shown in portion of the tilted E field doesn't create voltage in the Figure 1.

4 The antenna needs to be close to the ground antenna, but the horizontal portion does. The result is (as opposed to being high in the air) and works best induced voltage along the entire length of the antenna. over a ground area with medium-to-poor conductivity. Vertical vs. Horizontal Polarization Figure 2 shows a vertically polarized E. QS2111-Silver01 3. 4 to 5 at lowest f field. A horizontally polarized E field that's parallel and close to Earth is severely attenuated by ground losses. RX. T1. R=Z 0. Furthermore, if arriving along the 1:3 Turns Ratio antenna, the E field is at a right angle Ground to the antenna and can't induce Radial System voltage in it. That means the Beverage antenna is most sensitive to vertically Figure 1 A simple one-wire Beverage antenna with a resistive termination and a polarized signals arriving in line with 9:1 impedance transformer provides a good match to 50 coaxial cable.

5 The antenna. (Regardless of a signal's QST November 2021 55. original transmitted polarization, ionospheric propa ground below the wire. This unterminated, bidirectional gation always causes polarization rotation, known as Beverage receives signals from the front and slightly Faraday rotation, so the sky-wave signal arrives with less from the back.. a mix of vertical and horizontal polarization.). If the antenna is terminated with a resistance approxi- The Side and Top mately matching its characteristic impedance, the unde- Even if tilted, the vertically polarized E field of signals sired signal is absorbed at the end of the antenna and arriving broadside to the antenna is at a right angle to not reflected to the feed point.

6 We now have an antenna the antenna and can't induce voltage. Horizontally that attenuates signals in all directions, except from the polarized signals arriving broadside to the antenna direction of its terminating resistance. Figure 4 shows have an E field parallel to the antenna, but don't result the resulting pattern for 160-meter Beverages that are in strong received signals. 1 (545 feet) and 2 (990 feet) long. While the vertically polarized E field of a sky-wave Traveling-Wave Antennas signal is perpendicular or tilted with respect to Earth, The Beverage antenna is a traveling-wave antenna the horizontally polarized E field is always parallel to because it never has standing waves from reflections Earth.

7 When a horizontal E field is very close to Earth from the ends of the wire. As a result, it's also non- (much less than 1 4 ), it's significantly attenuated by resonant, and the antenna dimensions aren't required ground conductivity and can't induce much voltage into to be a specific fraction or multiple of the signal wave- the antenna. length. Beverages work well over a fairly wide frequency range where they're between about 3 4 and 5 long, When sky-wave signals arrive from nearly overhead, with good performance around 1 to 2 . both horizontally and vertically polarized E fields are parallel to Earth. They are severely attenuated when Transmission line close to Earth, before inducing a voltage into the The Beverage antenna has a characteristic impedance antenna.

8 And not a feed-point impedance. Like a dipole antenna, current in the Beverage 's horizontal wire creates an Front and Back electrical reflection or image on the ground below it. The The Beverage antenna develops a main forward beam current in the wire and its image create an unbalanced because wave fronts arriving at angles offset from the transmission line with a characteristic impedance. If this antenna induce progressively less voltage into it as the Beverage transmission line is terminated with that same angle increases. impedance, any signals flowing toward the termination are absorbed, as with any other transmission line . Most Figure 3 shows the Beverage antenna accepting sig- Beverages have a characteristic impedance of about nals from the front and rejecting them from the back.

9 If the right-hand end of the antenna in the figure is left open-circuited, a signal from the back reflects off the QS0604-Silver02. end of the wire, just like in an open-ended transmission Induced Wave fronts line . The signal then returns to the feed point, dimin- Voltages Arriving ished by a small amount of attenuation from the lossy To Receiver Ground Back Front Wave fronts Signal Arriving Absorbed To Receiver Ground Figure 2 Incoming signal wave fronts tilt at ground level, due Figure 3 Voltage waves build up along the antenna and are to reflection in the ionosphere and the effects of ground. either transferred to a feed line or absorbed by a terminating resistance.

10 56 November 2021 QST QS0604-Silver03. quencies. Longer Bever- 0. ages develop a Table 1 Recommended 330 30. progressively narrower Beverage Lengths 3 1 Beverage 6 pattern and better inter- Band Length 9. ference suppression 160 meters 500 1,200 feet 300 60. 12 80 meters 300 600 feet outside the narrower 40 meters 200 500 feet 18. beam. With a length above 5 , sensitivity 270 90 begins to decline because voltages and currents induced by the tilted wave front start interfering with voltages and currents traveling along the antenna to the feed point. 240 120. Speaking from experience, the Beverage wire should 150. 2 Beverage be high enough that animals don't run into it.