Civil broadcasting and radio were invented in the early 20 th century. In the last hundred years, radio broadcasting and radio technology have undergone earth-shaking changes. Since the era of AM (AM) broadcasting, the broadcasting mode has experienced the stages of FM (FM) broadcasting, FM stereo (FM STEREO) broadcasting, digital audio broadcasting (DAB) and so on.
At present, scientists are studying short band digital broadcast (DRM). The frequency used in civil broadcasting has experienced the stage of long wave (LW), medium wave (MW), short wave (SW), ultrashort frequency modulated (FM), satellite FM broadcasting. The range and coverage of broadcasting also ranges from close proximity to the use of artificial Earth satellites for global transmission; Radios range from ore radios, tube radios, transistor radios, integrated circuit radios, to digital tuned radios using microcomputer processors; Radio basic circuit form, also from direct amplification, to superheterodyne, multiple frequency circuit.
The size of the radio has also changed from bulky to miniature, while the sound quality is getting better and better.
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