AERIALISMS

Sun (Auckland), Volume III, Issue 693, 19 June 1929, Page 14

AERIALISMS

One of the worst, forms of interference, and one of the most difficult to dodge, is that from tramway systems. Generally speaking, an aerial under the roof is much better than an aerial wound round the picture rail. • • • When uwinding a new aerial wire be sure not to allow it to kink or bend sharply, as this will inevitably weaken it. • • * If you use an outdoor aerial it should be fitted with an earthing switch so that the aerial can be connected direct to earth outside the. house when not in use. If L.F. transformers are placed too close together in a set howling will often result, especially if their cores are not at right-angles. j High-tension power lines must be avoided like the plague when erecting aerials, or a fatal accident may follow. * * * Measuring instruments for checking the condition of batteries, etc., are essential where a three or four-valve set is employed for good quality recepI tion. Some H.F. chokes as used for capacity controlled reaction are not efficient on the long waves, although they [ may be perfectly O.K. upon the or--1 dinary broadcasting wave-lengths. * * * Many a good indoor aerial is spoilt by the fact that the lead-in wire from 3 aerial is placed too close to metal pipes or similar objects, which subtract a certain amount of the energy which should reach the set. If you have any spare fixed condensers on hand, no matter what the size, try the effect of connecting one of them in the aerial lead. (They cannot do any harm, and may improve reception.) Large fixed condensers connected across the contacts will generally reduce interference from flashing advertisement signs or similar sparking electrical machinery. If you are spring cleaning your set, do not forget that battery acid can be renewed quite cheaply, and may result in lengthening the life of your battery. When the detector valve is coupled to the L.F. stage by means of a resistance in its plate circuit, it is necessary to apply a much higher voltage than would be the case if a transformer were used here. When weak signals are being received it is very often an advantage to increase the value of the grid leak, and 4, 5 or 6 megohms is not an uncommon value to use in such circumstances. * * * For short-wave work it often pays to experiment with the value of the grid condenser, as generally a very much smaller condenser can be used than when an ordinary set is employed.

Generally speaking, where H.F. screening is attempted, it is better to screen the complete stage rather than the coil alone. One little-used method of dodging bad interference from electrical mains, etc., is to bury the aerial. (The buried aerial should be well insulated from the earth by means of rubber covering or similar protective material, placed just below the surface of the •rround, and running for 2oft or so in as straight a line as possible.)