Transmitters

The evolution of the type, form and scope of radio transmitters is traceable from the nascent technology of not yet a century ago to today´s elaborately sophisticated systems, among which are included radar, multichannel microwave, aircraft and marine communications and navigation and commercial broadcast. Apparatus and techniques progressed from the early spark and arc transmitters to alternators of various designs and powers, through the era of the first vacuum-tube transmitters to the later highly efficient vacuum-tube types. More recently, transmitter design has utilized high-power tetrode and klystron amplifiers. Although code signaling was the first practical method of communicating intelligence, interest in voice transmission resulted in concurrent efforts to adapt the then existing transmitters to this purpose. The discovery of ionospheric phenomena permitted advances into areas of transmitter development previously considered impractical for other than short-distance communications. Regulations governing transmitter power, frequency and use were established by government agency as the need became apparent. The regulations have been adjusted to keep pace with the increase in power capabilities and the use of the frequency spectrum as the trend continues toward higher-power transmitters.