Random Wire Antenna

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.

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

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