Communication Systems

COMMUNICATION SYSTEMS

Barriers to Human Communication

„X Language

„X Distance

Electronic Communications

The transmission, reception, and processing of information using electronic circuits.

History

mid-19th century ЎV James Clark Maxwell studied electromagnetic wave and predicted that it can be propagated through free space.

1837 ЎV Samuel Morse invented the telegraph.

1876 ЎV Alexander Graham Bell and Thomas A. Watson transmitted human conversation over a functional telephone system.

1888 ЎV Heinrich Hertz radiated electromagnetic energy from a machine he called oscillator.

1894 ЎV Guglielmo Marconi was the first to accomplish wireless transmission.

1908 ЎV Lee DeForest invented the triode vacuum tube.

1933 ЎV Major Howard Armstrong invented frequency modulation.

1948 ЎV William Shockley, Walter Brattain and John Bardeen invented the transistor.

Electromagnetic Spectrum

Electromagnetic Spectrum

The entire range of frequency.

Frequency

The number of times an alternating current goes through its complete cycle per second is known as its frequency. The international unit of measurement of frequency is hertz, abbreviated Hz. The English unit is cycles per second, abbreviated cps (1 Hz = 1 cps). It is rarely used.

To simplify terminology, 1000 Hz is called kilohertz, abbreviated kHz, and 1000000 Hz is called a megahertz, abbreviated MHz.

The vibration rate of sound waves in air may also use the term frequency. When middle C is played on a musical instrument, for example, an air disturbance with a frequency of 262 Hz is set up. The lowest tone that can be heard by human beings is about 15 Hz. The highest audible, audio, or sonic tones are usually 12 to 22 kHz (22 kHz for youngsters, 12 kHz for seniors). A microphone is a device or transducer that can change sound waves in air to an equivalent-frequency ac in wires.

Frequencies