ERECTING THE AERIAL

Radio Record, Volume I, Issue 1, 22 July 1927, Page 14

ERECTING THE AERIAL

SOME USEFUL HINTS

First of all the position of the aerial poles must be decided and in considering this it should be borne in mind that the direction of the aerial wire should be as much at right angles as possible: to any power, lighting ot tramway overhead wires or other aerial that may happen to be near. ‘The leadin picks up signals just as much as the horizontal portion of the wire, and is always included in reckoning | the length. Seventy feet is a good length for an aerial, but it can be much longer without detriment. ‘The shorter an aerial and the higher, the more selective it will be, but if the length is reduced to less than say fifty feet, it will be found that selectivity is being gained at the expense of volume. So the conclusion is that it pays to have a long aerial for bringing in distant stations, and this also applies to short-wave reception. Turret and lattice-work masts of various designs, though they often look quite handsome and dignified, are not to be recommended in windy situations as they offer too much resistance to wind-pressure, and on that account re- quire specially strong stays and anchors for the same. It pays to put up a good strong aerjal at the outset, and if proper attention is given to making a good firm job, very little further trouble will be experienced. Good poles can be made by bolting together a three-by-two and a two-by-two for each, to give thirty {vet or more in height, but where this height is impracticable, twenty or twenty-five feet will give -very good results. Where the local station is not far away and distance-getting is not to

be an essential factor, quite a low ontside aerial will give all that is desired, though for crystal reception it is always a good maxim not to cut the aerial too fine and to pay special .attention to the insulators, both on the aerial itself and on the lead-itt if any should be required there. Neither valve nor crystal receiver can afford to allow aerial losses, and if the lead-in must have its direction changed, let the insulator to which it is attached be of the post office or ‘"‘petticoat’’ pattern as these insulators are highly efficient. Stranded.

Galvanised clothes-line makes good strong and cheap stays. Single wire stays are apt to break with the vibration caused by wind, and the loss of one stay may mean breakage and collapse of the pole. Stays should be attached to the very top of the pole and not a foot or two below, as the latter method causes the weight of the aerial wire to gradually bend the — short length between it and the top of the, stays, spoiling the appearance, and weakening the pole. Insulators are not necessary in the stays if the aerial is only for receiving. If the poles are higher than twenty feet a set of stays should be attached half-way up to steady the centre of the pole. An important matter with high poles is to allow for plenty of spread for the stays. ‘he usual tetidency is to place the poles too near fences to which. the stays are attached, and thus not get sufficient angular pull to carry the strain properly. ‘This usually happens. at the bottom end of the garden: round the house there is usually more room for spreading the stays, so that it will in awkward cases whiere the section is short, pay to increase the height of the pole at the lead-in end and decrease the other in order to stay it more safeY. A single stranded wire is the correct thing for an aerial of ordinary length, and the lead-in should be a continuation of the same wire. In cases where it is impossible to erect an aerial of more than twenty or thirty feet, two or three wires separated at least two or three fect by wooden spreaders should be used, an insulator being placed wherever the wires are attached to the spreaders. The wires must only be joined together at the lead-in end. Aerials appear to be almost immune from being struck by lightning, even in countries where thunderstorms are more frequent and much more severe than in New Zealand, Insurance companies do not make any extra charge on the premium when an aerial is erected, provided that it is installed in accordance with the fire underwriter’s re-

gulations which stipwate that not less than 14’s copper wire shall be used tor the lead-in, and earth connection, anu that an efficient lightning arrester anu switch to earth the acrial shall be included im the aerial circwt. ~ Recent practice 1s to place the hghtning-arres-ter outside the honse near the lead-in, aud this should be done if possible, th. earth connection also running to ground outside the builuing. An ebonite lead-in tube purchased ready-made, if inserted through a hole drilled through the wall ot the house, forms a good method of getting the aerial connection through." ‘The inside portion from the lead-in to the set, whether covered wire or not, should be attached to a, small fixed porcelain insulator where it is necessary to turn a corner, but the wire should be kept several inches from walls and partitions, It is important to see that neither the poles nor aerial wire can swing, as that tends towards jerky and uncertain reveption, more especially on short-wave work. Keep the wire reasonably tight. Continuous rope halyards are best, and may run over a pulley-wheel running in an upright slot cut in the top of the

. pole, the spindle being a portion of a. large nait pushed through a hole drilled in the side of the pole across the slot. The lead-in must come out from the acrial at the very end of the wire at the first insulator, and not a iovt or two from the end. This 18 intjortant for technical reasons that n.ed not ke explained here. Trees growing near the aerial will be inclined to screen waves coming from their direction, and the only way to overcome this, short of cutting down the trees is to make the aerial Igher than the screening trees. People living next to each other someritnes get an idea that they can join at an aerial, or erect two aerials on one pair of poles. It is not feasible for two sets to use the same aerial at the same time, and with two aerials on the same pair of poles, results would not be very satisfactory if either of the sets heppened to be a radiator or howler.

"MEGOHM" WILL BE PLEASED TO ANSWER THE RE: QUESTS OF ENTHUSIASTS FOR CONSTRUCTIONAL DE: TAILS IN RELATION TO HOME: MADE SETS AND OTHER DATA. SHOULD ANY LIS: TENER OR ENTHUSIAST DE: SIRE A CONSTRUCTIONAL ARTICLE UPON ANY PAR: TICULAR ASPECT, EVERY EF. FORT WiLL BE MADE TO COMPLY WITH HIS REQUEST. ADDRESS "MEGOHM," BOX 1032, WELLINGTON. |