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DESIGN PROBLEMS IN TELEVISION 67
the signal be as narrow as possible in order that the signal may be transmitted as efficiently as possible and that there may be as many stations as possible in a given transmitting band.
The present standards that have been set up by the Radio Manufacturer's Association provide for the transmission of two separate carrier signals, one carrying the video signal, and the other the audio signal. The frequency-separation of the two carriers is specified in order that single-control tuning to any transmitter may be accomplished.
These RMA standards provide for the transmission of a video signal of negative polarity composed of 441 lines per frame, with 60 inter
FIG. 1. Television film projector, DuMont statio'n W2XVT.
laced fields and thirty frames per second. The television signal transmitted in accordance with these standards occupies a transmission band of approximately six megacycles. Synchronizing pulses are transmitted for controlling the sweep circuits that deflect the electron beam to generate the raster that develops the picture.
The receiver designed for such a transmission system must have circuits designed for this type of signal alone. Any variation from the standards will destroy the picture, and if any such variations were to be adopted in the future they would cause the obsolescence of all existing receiving equipment.
Engineering progress comes only through constant, continued research and development. It is obvious, therefore, that at some future