Discone Antenna Design

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Fig. 2. The 80m wideband antenna at ZS6ZO. Two dtpoies spaced 90 degrees apart are fed 90 degrees out-of-phase with an electrical quarter-^avefength interconnecting tine Shields of lines are all soldered together at dipole feedpoint and connected to adjacent antenna sections, plan accordingly when choosing wire and msulators li used wire for my antenna, and experienced no mechanical failures. The spreaders were fashioned from some Plexiglas™ that I had on hand at the time However they could be made of wood or PVC Conductors such as angle aluminum have also been used tor spreaders, although some claim thai doing so increases the antenna Q and hence markedly decreases bandwidth.

Attempting to erect a cage dipole in an area cluttered with underbrush and overhanging limbs can be a nighlmare (trust me, I've tried it)H but if you can suspend one wire near ground build the remainder ol the antenna around that wire, and then pull the complete assembly into position, the task is not especially difficult.

Another dipole cousin is the fan dipoie 0 As can be seen in Figure 4, each side of a fan dipole con* sists of two arms 55 feet long, spaced 12 feet from one another at the ends, and joined ai ihe center The antenna is 1 to feet long, causing it to have a capacitive reactance on 80-meters To compensate for that reactance, a reactance of opposite sign {ue.h an inductor) is connected across (he antenna terminals (see Figure 4 for details). This procedure also

Meters Antenna
Fig. 4. Broadband fan dipole for 80m. Wires may be either m the horizontal or vertical plane The inductive reactance (XL) is 64 Ohms. At 80m. L 2.7 uH; this is achieved by winding 8-1 2 turns of *12 wire around a 2 -long, 2 -diameter tube.

transforms the resistive component seen at Ihe anlenna to approximately 50 Ohms

W7IS, has his own version of a wideband dfpole for 80-meters (Figure 5) As you can see in the illustration, he uses five equal length wires connected in parallel for each leg of the dipole. The wires are spaced approximately 2 feet apart, with no spreaders be-:ng used. W7IS alarms an swr of less than 2:1 ever the 80-meteF band with thrs antenna. Although he used a 1 1 balun ai the feed-point of this antenna, I suspect that it would work equally well v ith direct coax teed.

The discone and conical monopole (Figures 6 and 7) are two wideband verrically-onented antennas that not only covers all of Ihe 30/75*meter band with a low swr. but works well over several ad|acent amateur bands. Their shortcoming is that they take up considerable real estate when designed for ihe iower HF bands. Due to their limited application, interested readers are referred *o the ARRL Antenna Book (edit on 13) and an article by Star. Gibihs-COW1GVM m the Way 1985 issue of 73for funher details

The antennas discussed above certainly do not constitute an exhaustive iist of he wideband antennas that can ue used or\ 80-meters. However, they do provide some examples of how you can erect an antenna that yields a relatively low swr over ihe

Meter Dipole Antenna

Fig. 1. Top View of the broadband stagger-tuned: crossed dipole antenna.

Fig 3 Cage dfpole The spreaders are spaced at W-15 intervals

40m 80m Dipole Ant

Ftg. 5. W?lS's 80m wideband dipole.

3 5 to 4-MHz range And don t forget that these antennas can also be scaled for use on the other amateur bands lhat have relatively large bandwidths* such as 160 and 40 meters. So, give one of these antennas a try and free yourself from antenna-tuner slavery. I'm interested in hearing how they work for you and what new ideas readers have for these (and other) antennas ST

References

1 Logan, Mason A., "Stagger-tuned dipoles increase bandwidth/' Ham Radio, May 1983, p.22-24

2. Grr, Bifl "Ham radio techniques—the 2S6ZO wideband 80-meter antenna. Ham Radio, June 1984, p 60

Discone Antenna Plans

Ftg 6. Discone antenna L = wavelength/4 (free space) at lowest operating frequency. S = 1-6 inches.

3. The ARRL Antenna Book, ed.13, p.30

4. Harbachr Alien 8,, "Broadband 80-meter antenna, QST. December T980. p.36-37

5 Johnson David C . Technical Correspondence—Cage antennas," GS7"November 1983, p.61

6. Orr, BilEt "Ham radio techniques—broadband dipoles/' Ham Radto. October 1983. p.66

7. Orr, Bill, "Ham radio techniques—a wideband 80-meter antenna/' Ham Radio. July 1987, p.57.

Fig. 7 The conical monopole antenna. Ai B top view shows the dimensions for 3.5-14 MHz. At C is shown the side view of the conical monopoie ai section A-A. Note that the grounding stubs, b, connect to the short radial wires; a Wires c run up the sides of the supporting poter which is unguyed r

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  • birikti welde
    How to build a 10 meter cage antenna?
    5 years ago

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