Radio Broadcast (Nov 1924-Apr 1925)

858 Radio Broadcast electrically identical, no matter where secured, is unfortunately erroneous. There are many differences between one power circuit and another. First, there are wide variations in voltage at different hours of the day and night ranging between 100 and 1 20 volts. These are not noticeable in the brilliancy of electric lights or in the operation of ordinary household equipment, largely because this apparatus unlike radio equipment, is not especially sensitive to voltage variations,of this amount. In a current tap supplying a radio set line voltage differences are of the utmost importance. Another factor, which enters into the matter of successful current tap operation in one's particular location, is the voltage wave form delivered by the generating system supplying the alternating current. The theoretical sine wave, with its smooth variations, is a laboratory product only; alternators supplying power lines have individual characteristics which cause humps of differing intensity, to occur in the voltage at harmonics of the 60 cycle frequency. Engineers state that no two generators have ever been built that have precisely the same voltage curve and that an expert can recognize the wave form of a particular generator with the same degree of accuracy that a detective identifies the criminal by his finger print. Such variations in wave form have no effect upon the ordinary loads, such as motors and electric lights, but a vacuum tube rectifier is so highly responsive to these digressions from the sine wave, which often assume proportions larger than the voltages induced in the antenna system by strong incoming signals, that satisfactory reception with the current tap may be impossible. Consequently, one current tap device, silent when supplied from one light socket, may be objectionably noisy in another. THE OUTPUT OF A COMMERCIAL ALTERNATOR Installed in the average power house which furnishes the alternating current used for house lighting and power purposes POWER TRANSFORMERS AFFECT CURRENT ANOTHER important cause of changes in wave form are those due to saturation of the iron core of transformers placed along the line to step down the line voltage to the value required by consumers. At certain loads, this effect may accentuate harmonics to a surprising degree, while at other hours and loads, they may fall to a point where they are not annoying. Hence a discriminating purchaser will not only test a current tap in his own home but will continue it over a sufficiently extended period to make certain that it will give satisfaction at all loads and conditions of his power circuit. Because of the newness of current tap devices, many dealers are willing to permit such a test and to refund the purchase price if satisfaction is not secured in your home. These considerations with respect to variations in power supply should not lead the reader to conclude hastily that a current tap device cannot be made to work. If it is provided with suitable adjustable inductances, capacities and resistances, its characteristics may be adapted to these constantly changing conditions. In judging the effectiveness of a current tap device in your particular location, it is also necessary to remember that power lines are excellent conductors of currents of radio frequency, as evidenced by the successful development of antenna plugs for use in place of aerials, and the transmission of radio programs over power lines, by the "wired wireless" method. Those who live in or adjacent to buildings having elevators or electric motors have frequently heard the annoying hum which is radiated from the power lines and picked up by the antenna system. In some cases, it is necessary to wait for the offending elevator to complete its trip before satisfactory reception, even from local stations, can be secured. When using a current tap device you make a direct connection with the power conductors supplying such elevator motors, amplifying the resulting noises through vacuum tubes and feeding them to the most sensitive circuits of your receiving set. The interfering noises from such sources are therefore tremendously increased. Every time a light is switched on and off in the building, a decided click is heard, although noise from