ON SHORT WAVES

Dominion, Volume 26, Issue 163, 5 April 1933, Page 6

ON SHORT WAVES

Nature of Power Supply HINTS FOR SET OWNERS It is true to say that the main factor governing the choice of any type of broadcast receiver is the question of the power supply available, and this is not less true for a short-wave receiver. If the supply is alternating current, the most convenient type of short-wave receiver is one which takes its supply from the mains ■without the use of batteries. The actual current consumption of a wireless set is very low, being only of the order of 40 to 60 watts, i.e., that taken by an ordinary electric lamp.

If electric mains are not available at the point where the receiver is to be used, but if either electric mains or battery charging equipment is available at a short distance from the place where the receiver is installed, a good solution to the pow-er. supply difficulty would be to install accumulators both for low tension and high tension supply. Another method is to use a large capacity low tension accumulator, which not only provides the low tension supply direct, but which is also used to drive a small rotary convertor which provides the high tension supply. Special precautions have to be taken to prevent the convertor from creating electrical disturbances which interfere with reception, but machines are now available which are specially designed for the purpose,.and which incorporate the necessary silencing device to suppress this interference. It is, of course, necessary that there should be no serious difficulty in recharging the low tension accumulators. This method has the advantage that the heavy duty low tension accumulator is very much more robust than the small high tension accumulators, and is less likely to be damaged in transit for re-charging. Indeed, the normal type of accumulator battery, fitted as a starting and lighting battery on a motor-car, is entirely suitable for this purpose. Yet another method of obtaining high'tension supply is by the use of dry high tension batteries. The initial cost of these is considerably less than that of high tension accumulators, but they cannot be re-charged when exhausted and have to be thrown away.

It is not possible to judge the performance of high tension . batteries in hot climates merely from a knowledge of their performance in a temperate climate, where they are used in very large numbers and with entire satisfaction for this purpose. In tropical and humid climates It may be found that a type of cell known as the “inert” cell may be advantageous. This type of cell is not rendered active until it has been filled with water.