Surveyof

Electronics

Development of Electronics

Wireless transmission can be taken as starting with the work of Heinrich Hertz, a German physicist. In 1887 he was the first to demonstrate by experiment the process of electromagnetic radiation through space. The distance of transmission was only a few feet.

Hertz proved that radio waves, although invisible, travel with the same velocity as light waves. In fact, radio waves and light waves are two examples of electromagnetic radiation.

The work of Hertz followed earlier experiments on electricity and magnetism. In 1820, a Danish physicist, H. C. Oersted, showed that an electric current produces magnetic effects. Then, in 1831, a British physicist, Michael Faraday, discovered that a magnet in motion can generate an electricity. In 1864, the British physicist James Clerk Maxwell, on the basis of work in electricity and magnetism., predicted the electromagnetic waves demonstrated later by Hertz.

In 1895, Guglielmo Marconi used a long wire antenna and developed a practical radio system for long-distance communication. He succeeded in producing wireless communication across the Atlantic Ocean in 1901.The rapid advances after that are due largely to the introduction and progress of the vacuum tube. In 1906 Dr. Lee De Forest, with his audion tube that could amplify electric signals, was a leader in this field.

As the design of vacuum tubes advanced, radio broadcasting progressed rapidly. Regularly scheduled programs were broadcast in 1920 by station KDKA in the AM radio band. The commercial FM (frequency modulation) broadcast service for sound programs was started in 1939. Stereo broadcasting in the FM radio band began in 1961.

With regard to television, after discarding previous mechanical systems that used rotating drums or disks, commercial television broadcasting was adopted officially in July 1941, although its popular use did not begin until 1945. Our present color-television system was adopted in 1953.

Now, with the invention of transistors in 1948 at Bell Telephone Laboratories, there are new applications in electronics and radio. The transistor is an application of controlled electron flow in solids such as germanium and silicon. Tubes and transistors both have similar applications for amplification. The transistor is smaller, however, and more efficient. Solid-state electronics using semiconductors includes not only transistors and diodes but also the integrated circuit (IC). It combines these semiconductor components in one solid chip with the required resistors and capacitors.

Wireless BroadcastingBroadcasting means to send out in all directions. The transmitter sends out electromagnetic radio waves radiated from its antenna. Receivers can pick up the transmitted radio signal by means of a receiving antenna or aerial. The leader reproduces the desired signal transmitted by the broadcast station.The electromagnetic wave is a RF carrier signal with AM. The amplitude or strength of the RF carrier varies in step with variations in the desired voice or music information, which is the audio signal.A higher-frequency carrier wave is chosen for the best radio transmission. Its modulation provides the desired signal information.

Radio Broadcast ServicesRadio is an abbreviated form of radiotelegraph and radiotelephone. The word radio means radiation for wireless transmission. At first, communication was by radiotelegraph, using short dots and long dashes in the Morse Code. Now radiotelegraph is used more for voice communications and for broadcasting voice and music programs for entertainment.The transmission distance for wireless communication can be less than a mile or as much as 5000 miles, depending on the type of service.

All radio services in the United States are regulated by the Federal Communications Commission (FCC). The FCC assigns the RF carrier wave for transmission and monitors use of the airwaves.

A few of the most important radio applications are described here briefly.-Standard AM Radio Broadcast Band-FM Radio Broadcast Band-Television Broadcasting-Amateur Radio-Citizen’s Band (CB) Radio

APPLICATIONS OF ELECTRONICSThree logical groupings of electronics applications1.Communications electronics – includes AM radio, FM radio with stereo, and television with color. The equipment is divided between transmitters and receivers. Also transmitters can be divided between radio-frequency equipment. High-fidelity audio equipment can be considered with radio receivers.2.Electric power – These applications are in the generation and distribution of 60-Hz ac power, as the source of energy for electrical equipment.3.Digital electronics – We see the digits 0 to 9 on an electronic calculator or digital watch, but digital electronics has a much broader meaning. The circuits for digital applications operate with pulses of voltage or current.

In addition to all the general applications in communications, digital equipment, and electric power services, several fields that could be of specific interest include:-Automotive electronics – more and more electronic equipment is used in cars for charging the battery, power-assist functions, measuring gages, and monitoring and control of engine performance.-industrial electronics – includes control of welding and heating processes; the use of elevator control; operation of copying machines; metal detectors and smoke detectors; moisture control; and computer-controlled machinery.-medical electronics – combines electronics with biology. Medical research, diagnosis, and treatment all use electronic equipment.

JOB TITLES

Different specialties in electronics are indicated by the following titles for engineers: antenna, audio, computer, digital, illumination, information theory, magnetics, microwave, motors and generators, packaging, power distribution, radio, semiconductor, television, and test equipment.

ELECTRONIC COMPONENTS

1.Semiconductors2.Electron tubes3.Visual display devices4.Resistors5.Capacitors or condensers6.Inductors or coils