RTV Theory and Practice - Special Issue

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ALL -DIGITAL AM BROADCAST SVSTEM WITH GATED IMPULSE MODULATION Кеу to diagrams: 1. Music and other audio is pre-recorded on digital tape or compact đisk . Piayer outputs string of digits representing original material. 2. Announcer's voice and other analog audio is changed to digitai in A/D converter unit. 3. Computer unifies all digital stanđards, performs miking, fading, level balance and processing f unctions. 4. In transmitter exciter, Gateđ Impulse Modulator converts incoming digital information into GIM binary form . 5. Ultra-efficient switch-mode amplifier in transmitter boosts power of GIM signal to authorized level (e .g . , 10 , 000 watts ) . 6 . Passive GIM/AM converter changes Gated Impulse Modulation train into standard Amplitude Modulation envelope for radiation from antenna . Digital communications experience can likewise be applied to AM receifers , most of which have circuitry about half as sophijticated as that used for FM. For example, the application of p)ase-locked-loops has gone far to ensure drift- and fadeffree pickup of FM . Similar circuits could assist AM , particularly in fringe areas and from moving

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