Transmission Of Picture Iformation: An amplitude-modulated wave commonly re-[uires a bandwidth that is twice the highest fre-[uency of the modulating signal. For AM radio iroadcast, for instance, this bandwidth is 10 :Hz; it consists of two 5-kHz sidebands cen-ered about the carrier frequency (Fig. 7). In his case the frequency of the modulating signal 5 limited to 5 kHz. This limitation, which was nposed to accommodate as many AM stations as ossible with the broadcast band, is the main sason why these stations cannot provide high-delity reproduction of music. Besides standard iM radio broadcasting, other common uses of ^M systems include the transmission of picture iformation in television broadcasting.
Radio transmission generally occurs in one of three ways: (1) ground-wave transmission along the earth's surface; (2) sky-wave transmission reflected downward from the ionosphere to a distant receiving antenna; and (3) direct line-of-sight transmission from the transmitter to the receiver (Fig. 5). A fourth way, scatter transmission, is used for some special services. See section 5. Special Applications of Radio (Tropospheric Scatter Systems).
Transmission Line. An electrical transmission line connects the transmitter to the transmitting antenna. The antenna may be located a considerable distance from the rest of the transmitter, as it usually is for broadcasting, or the antenna may be rather close, as it is for police mobile radio. In both cases the transmission line should match the transmitter to the antenna and also prevent radiation loss from the line.
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Photography
