Random Wire Antenna

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A "Random Wire" antenna is an end-fed antenna that is operated against ground or an artificial ground system - much like a vertical antenna. The "Random Wire" must normally be coupled to the transmitter by an ATU (except if it happens to be in resonance on some amateur band).

A popular length is 7m. This does not provide excessive impedances for the ATU to tune out for bands between 80 and 10m.

Jack Clarke VE3EED adds that for optimum performance, "random length" antennas should not be multiples of half wavelengths in the intended bands. The following table reproduced with permission from his website details half wave lengths that should be avoided (all measurements are in feet):

Frequency MHz 1/2 Wave 2nd Multiple 3rd Multiple 4th Multiple
1.9 246 492 738 984
3.8 123 246 369 492
7.2 65 130 195 260
10.1 46 92 138 184
14.2 33 66 99 132
18.1 26 52 78 104
21.3 22 44 66 88
24.9 19 38 57 76
28.5 16 32 48 64

Further calculations by Jack led him to produce the following list of "preferred" list of antenna lengths, to avoid half wavelengths and their multiples (measurements in feet):

29 35.5 41 58 71 84 107 119 148 203 347 407 423

Advantages and Uses

A random wire Antenna is used in conjunction with an antenna tuner to achieve resonance over a range of bands. The advantage being that it can be used without the need to make physical reconfigurations to the antenna system in order to change bands.

Basic Construction

The basic design of a random length wire Antenna consists of a driven wire of a length that does not correspond to the wavelength of the intended Band and a grounded plane of conductive material such as steel. It differs physically from a Vertical in that ???.

Antennas
Design Beam * Dipole * Dish or Parabola * DDRR * Log Periodic (LPDA) * Loop * Mobile and portable * Omnidirectional * Panel * Quad and Quagi * Screwdriver * Small tuned loop * Vertical * Yagi-Uda * Wire and random wire antennas
Installation Antenna Tuners * Capacity hats and loading coils * Cavity filters * Coaxial Cable * Feedlines * Rotators * Towers and Masts * VK2ACY - G5RV coupler
Theory Front-to-back ratio * Impedance matching * SWR * Tower design * Vertical Antenna efficiency * Wire comparison tables