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
radiation through space. The
distance of transmission was only a
Hertz proved that radio
waves, although invisible,
travel with the same velocity
as light waves. In fact, radio
waves and light waves are
The work of Hertz followed earlier
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
radio system for longdistance
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
broadcast in 1920 by station KDKA
in the AM radio band. The
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
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. Solidstate 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.
Broadcasting 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
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 Services
Radio 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
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
-Citizen’s Band (CB) Radio
APPLICATIONS OF ELECTRONICS
Three logical groupings of electronics applications
1.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
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
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 computercontrolled machinery.
-medical electronics – combines electronics with
biology. Medical research, diagnosis, and treatment
all use electronic equipment.
Different specialties in electronics are
indicated by the following titles for
engineers: antenna, audio, computer,
digital, illumination, information theory,
magnetics, microwave, motors and
distribution, radio, semiconductor,
television, and test equipment.
3.Visual display devices
5.Capacitors or condensers
6.Inductors or coils