NOISES TRACED

Sun (Auckland), Volume I, Issue 238, 28 December 1927, Page 14

NOISES TRACED

CAUSES OF RADIORACKET NEARBY ELECTRICAL EQUIPMENT The various hums and crackles that the radio listener hears at times in his loud speaker are principally caused by motors, thermostatic controls, bad electrical contacts and current leaks, according to a manual recently issued by the Radio Manufacturers’ Association. Radio “racket,” as it is often called by the listener, the R. M. A. investigators of the interfence question declare, is due to the propagation of high-frequency currents generally through spark emanation. And spark emanations are caused mostly by bad contacts in some near-by electrical machine or equipment. Motor noises are due to bad brush contacts, the manual states. Thermostatic controls are silent except when making or breaking a contact. Leaks are the results of contacts where they ought not to be. And bad contacts are, of course, bad contacts. Set Up Wave Trains Sparks produced at such sources set up high-frequency wave trains, which, unless side tracked, are careried out on to the power lines and broadcast with considerable effect on the ear and temper of the community. They are readily by-passed by small condensers —in all cases where small amounts of current are used these condensers are generally from one-quarter to one-half mfd. And where they prove particularly obnoxious they may be kept off the line by means of radio frequency chokes. The simple statement of the situation does much to clarify a popular misconception of the means required in the shooting of radio trouble. One has only to take an inventory of his household electrical devices and eliminate them from his problem of making sure that they are all turned off. This will immediately narrow the field of search to defective contacts in fuse or light sockets, convenience outlets, light lines or bell ringers within the house, or possibly some difficulties of the same nature in the plate current supply. It is pointed out in the manual, that if every householder would make a comprehensive test in own home, outside troubles could be speedily isolated and dealt with simply and easily by power company engineers. CHASSIS-BUILT SETS “Chassis-built” sets—sets built on a cast iron or aluminium frame—have gone a long way toward freeing sets from the annoyance of broken and loose connections, giving a general air of sturdiness and permanency that perhaps has previously been lacking. Gradually these improvements find their way to New Zealand, but there is not always need for the listener to wait for them. Too often battery connections are but an untidy tangle of wires, the key to the unravelling being only in the hands of the one who connected the set up—who is not always too sure of it, even then. Bad connections, which give constant trouble, valve sockets that cause valves to function erratically—all are totally unnecessary, and bring the set a long way from ideals of simplicity. Battery chargers, eliminators, and aluminium chassis represent essentials of the ideal set, but these as yet are not given to the multitude, whereas a little method and orderliness are within reach of even a wireless enthusiast. RADIO AT THE SEASIDE This year almost every other bach has an aerial, some of the very temporary type, others more pretentious and obviously a permanent job. The writer wonders how many of these licencees have fulfilled their obligations and taken a temporary permit for the removed set. This temporary permit is necessary and costs nothing. Onb merely presents the regular licence form and gives the location and duration of stay to the departmental official. Reception in these quiet little bays across the harbour is exceptionally good, and it is commonly spoken of as being worth an extra valve to be on the northern side of the Gulf. The writer has a seven valve set installed at the bach, and Wellington comes in with magnificent volume during the day time, all the induction noises are gone and though there must be at least 20 aerials in the neighbourhood, a howling valve has not been heard since leaving town.