Radio broadcast .. (1922-30)

CHARACTERISTICS OF TELEVISION SIGNALS (Continued from page 319) is only necessary to employ synchronous motors of the same speed for rotating both mechanisms. Temporarily, while the television audience consists mainly of amateurs interested in results with the minimum expenditure, this method is ideal. However, as the service areas of visual broadcasting stations are increased it will become necessary to employ more intricate means of synchronizing. A synchronizing tone, let us say 720 cycles (which is the scanning frequency of a 48-line picture at 15 pictures per second), is transmitted to the receiving point. 1000 . 10000 FREQUENCY IN CYCLES Fig. 11 This may be supplied by a photo-electric cell operated by a light ray passing through the scanning apertures or by a small alter- nator operated from the same motor as the scanning mechanism. This 720-cycle signal may be transmitted to the receiving point as a modulation of a second carrier, or as a modulation of a 30-kc. wave which in turn modulates the same carrier as the picture signal, or it may be intermixed with the picture signal in the correct pro- portion. In the first two cases it would be necessary to employ two receivers or a special receiving system of the "double- modulation" type. The third case merely involves a filter circuit arranged so as to remove the 720-cycle component from the last stage of the picture amplifier. The synchronizing signal is employed sepa- rately and applied to a 720-cycle motor operating the scanning mechanism. In or- der to reduce the power required in the synchronizing motor, two sources of power are employed. A simple d.c. or a.c. motor supplies enough power to neutralize the friction and windage losses and starts the scanning mechanism in rotation. The 720- 180 W VOLTS Fig. n cycle synchronous motor serves merely to maintain rotation and synchronous speed. In starting up, the power input to the first motor is raised so as to pass through the re- quired speed, and then the motion is re- tarded until interlocking occurs. Errors in Adjustment Certain aspects of the image indicate errors in adjustment which may be readily corrected if they are borne in mind. Thus an inverted picture tells us that the scan- (Continued on page 358) CASH On a New Demand Every city and town offers opportunities for the sale and installation of sound equipment, and local radio dealers are the logical men to cash in on this demand. Wright-De Coster Reproducers and horns are meeting with tremendous success wherever in- stalled—for either indoor or outdoor use. WRIGHT-DE COSTER REPRODUCER There is a most efficient type of equipment for every purpose ranging from a tremendous battery for outdoor or arena use to single units for theatrical use and smaller sizes for home radio. Reproduced from RADIO January, 1930 Public ceremonies of all kinds such as in the dedication of new buildings, public institu- tions, memorials, etc., offer opportunities for the sound equipment specialist. Formerly, if one man could talk to a hundred people with- out straining his voice he was lucky. If peo- ple cannot hear clearly what is being said they soon lose interest. Today, with good ampli- fier equipment and reproducers, one person can make himself heard by many thousands, and a large proportion of those thousands can actually see the one who is addressing them. Amplification brings the individual to the multitude as never before. 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