TECHNICAL

Evening Star, Issue 23325, 22 July 1939, Page 4

TECHNICAL

STATIC ELIMINATORS. Not much is heard of static eliminators, contrivances which a few years ago were acclaimed Rs infallible extinguishers of electrical discharges. Unfortunately these eliminators were much like noise-reducing systems—they cut down tho radio signals in exact proportion to tho reduction of obnoxious noises. The fundamental difficulty is that the aerial picks up static just as it absorbs other discharges, and there are untold riches in store for the man who can devise an antenna system that will be selective enough to distinguish between static and stations. Apart from switching off the set, there is only one known way of cutting out Static. That is by earthing the antenna, but that is not exactly helpful, as station signals go to tho ground along with the others. « * * # LIGHTNING ARRESTERS NEEDED. It would be interesting to learn whether the many radio receivers damaged by lightning in various parts of the Dominion recently had their electric systems earthed through a lightning arrester. When receivers were comparatively rare the risk of damage or even fire through the antenna being struck. by lightning was seriously regarded” and insurance companies made special regulations in connection therewith.

So seldom, hoa'ever, has damage been reported that it is believed that many installations are made without the arrester equipment. Close observation shows that many local radio sets arc not fitted with lightning arrestei'4. As tho cost is so small this should never be omitted.

IMPORTANT FOR RECEPTION, . The listener will be well repaid if he gives dose attention to his choice of a ahort-Wave receiving set when Davetitry reception is An aim. The following points Should be watched particularly: —Buy a set made by a well-known manufacturer, and make sure that spare parts, especially valves, can be obtained; make sure that the receiver covers all the wave lengths at present used by Daventry from 13.92 to 49.59 inetres; make sure- that the receiver is sufficiently sensitive on the shortest

wave lengths, and that the receiver is able to separate adequately two transmissions on wave lengths which are Very close together. It cannot bo too strongly stressed that an efficient aerial and earth are essential. As a rule listeners will probably be content with an aerial consisting of a straight wire about 60 to 80 feet long and as high and free from buildings, trees, and other wires as possible.