CHOICE OF AN ANTENNA.

New Zealand Herald, Volume LXVII, Issue 20482, 6 February 1930, Page 5

CHOICE OF AN ANTENNA.

EFFECT ON RECEPTION. The average good receiving antenna is a single wire run horizontally between two vertical uprights and at light angles to, and a? far as possible awav from, power lines, or ol her sources of electrical interference. It should be placed as high and as free as possible from other obstructions or metal structures of any kind. As a rule, both the length and the height are controlled by local conditions and the available local facilities, such as chimneys, already erected, poles, skylights, etc. The person making (lie installation should look around and 'pick the vantage points that most nearly check up with the ideal antenna conditions before putting up the wires;

A short antenna gives greater selectivity at reduced signal strength and in general less static. It makes very little difference whether or not an antenna is indoors or out, provided it is equally free from grounded metal or large pieces of metal likely to affect antenna capacity. A metal roof, metal lath or reinforcing rods, metal beams, columns, etc., act as shields, and, as a rule, antenna placed close to them arc practically worthless. The antenna should be kept several feet from all metal where possible. It is a common error, declare radio engineers, to assume that antenna performance depends on the number of feet of multiple-wire antennae. Of course, such devices may in some cases produce good results, just as chandeliers, ground wires, etc., but such procedure is to be avoided if reliable results arc to be the rule rather than the exception. Freak antennae along with largo wire loops and loading coils placed either at the end or intermediate between the end and the receiver should not bp used. The latter is particularly objectionable, since it makes accurate compensation of the first tuned stage, possible at only one wave length. The greatest difficulty in operation of a portable radio receiver is finding a suitable aerial and ground. While some commercial portable receivers use a small loop, the majority of radio experimenters are inclined to use a simple set that will require an aerial. The well-known aerial consisting of a short length of flexible insulated wire thrown over the limb of a treo probably has been tried by many. This method is anything but convenient, and signals arc not any too strong. Likewise the ground for a portable set is also a problem, probably the most common being a counterpoise formed by running a length of wire along the surface of the ground beneath the aerial hung from the tree branch. A very satisfactory aerial and counterpoise is a.barbed wire fence. By connecting the aerial post of a set with a battery clip to the top wire of the fence and the ground terminal of the set. with thq bottom wire of the fence good results can be obtained.