What is a Random Wire Antenna in Ham Radio?

What is a Random Wire Antenna in Ham Radio?

Random wire antenna, as the name implies, is a random length of wire suspended high above the ground, usually between buildings or trees. It is a simple way of going on the air quickly when the usual types of antennas cannot be installed fast as in the field setting. Random wire antenna is also sometimes called as long wire antenna, though it is not absolutely correct. A long wire antenna has to be at least quarter wavelength or better one full wavelength of the operating frequency. Wires at even multiples of quarter wavelengths will have very high feedpoint impedance which cannot be matched with an antenna tuner. Hence it is important to avoid even multiples of operating wavelengths, though it is called a random wire antenna.

An important disadvantage of a random wire antenna is that the wire radiates up to the point where it reaches the antenna tuner. This would be picked up by the metallic parts of the radio and any attached devices and give you a burning sensation when you come in contact with them. This becomes more as the power output is increased and may be significant at 100 watts though it might not occur at low power.

Random wire antenna needs a good Earth ground, which could be a cold water pipe if you are in the lower part of the building. If the shack is located higher up a counterpoise is needed. Counterpoise is just a long insulated wire attached to the ground connection of the antenna tuner. Ideally it has to be quarter wavelength of the lowest operating frequency. As it is quite long for 80m it can even be looped around. Counterpoise will balance the antenna system from an electrical standpoint. Random wire antenna is sometimes deployed in a zig-zag fashion if there is space constraints, but this will reduce effectiveness and make theoretical analysis quite difficult.