RTV Theory and Practice - Special Issue

heretofore reserved for ГМ and pre-emphasis imwediately adding crisp highs to the reception . As countries and regions adopt pre-emphasis and sharp cutoff filter standards , two wonderful things will happen to AM reception ; First , the irritating whistle associated with nighttime reception will đisappear аз second channel interference is eliminated . Second , manufacturers will produce wide band AM receivers capable of much greater fidelity once they đon-'t have to muffle out that interf erence . The complacency of AM broadcasters has very nearly resulted in their demise in some countries . From this experience shoulđ came not only remedial action , but also vigilence; to maintain the medium current with the state of the electronic art, anđ to foster and promote research and development conducive to its constant improvement. ALL-DIGITAL AM BROADCAST An example of what the future might have in store is digital AM . The author is presently patenting a new system of AM transmission called "gated impulse modulation" (GIM), a method of combining clock (carrier) and information (modulation) in a single binary signal train which can be amplified by high-efficiency solid state switching circuits to апу desired power level before conversion to a conventional AM envelope for broađcast. GIM is entirely đigital, and offers significant advances for AM's future: 1 . A đramatic increase in power efficiency , typically double the 35-45Х prevalent in the industry . A transmitter now requiring 25 kW input power to produce a fully-modu!ated 10 kW carrier on the air might need only 12 kW to achieve the same output employing gated impulse modulation. Such efficiency levels are directly comparable to FM . 2. All-digital AM broadcast. The illustration below depicts how digitized audio entering f rom a CD , DAT or other source can directly input a transmitter with GIM , making possible a totally digital format from audio source to transmitter outpjt. This gives the broadcaster virtual control over transparenc/ , f idelity , and immunity f rom noise , hum and distortion , as well as the ability to computer -process the entire signal.

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