ELECTRONIC COMMUNICATIONS
I. Introduction
A. Humans have always communicated their ideas and feelings.
B. Throughout human history, people have looked for ways to communicate
over longer distances.
1. Out of this desire came electronic, or wave, communications.
C. This type of communication not only requires a message; but also is highly
dependent upon hardware to complete the communication process.
II. Electrical Principles
A. All matter is made up of atoms.
1. basic parts:
a. protons (positive charge)
b. neutrons (no charge)
c. electrons (negative charge)
B. In certain situations, electrons will travel from one atom to another.
1. This movement is called electron flow.
a. another word for this “electron flow” is electricity
2. The materials that permit the greatest amount of electron flow are
called conductors.
a. examples:
*gold
*silver
*copper
*aluminum
C. Types of electron flow:
1. direct current - the electrons are flowing in one direction only
2. alternating current - the electrons flow in both directions
a. this reversal occurs at regular intervals
D. Key principles of electron flow include:
1. magnetic lines of force (emf) - given off by moving electrons
2. induction - flow in one wire causing flow in another wire
3. transducers - converts pressure waves to electrical waves & vice versa
4. frequency - number of cycles per second (Hertz)
5. amplitude - strength of the wave (higher = stronger wave)
E. Electronic communication uses changes in the amplitude and/or frequency
of the waves to carry a communication signal.
1. radio waves - 30 Hertz to 300 gigahertz (300 billion cycles per second)
a. sound you can hear - 30 Hz to about 20 kHz
b. underwater communication - 10 Hz to 13.6 Hz
c. broadcast frequencies (above audible sound)
*police and fire department radio
*broadcast radio
*cellular telephones
*television signals
*military communications
III. Electronic Communication Systems
A. Electrical frequencies can be used to communicate data, information,
or ideas.
B. They are used in two major types of electronic communication systems:
1. hard-wired systems
2. broadcast systems
C. In hard-wired systems, the electrical codes are usually conducted over a
permanent wave guide that connects the sender and the receiver.
1. primary permanent wave guides:
a. copper wire
b. fiber optics
D. Often, a special system, called multiplexing, is used to increase the capacity
of the wave guide.
1. Allows several unrelated messages to travel down a single conductor
at the same time.
a. time division multiplexing
*message broken down into bits and by time
b. frequency division multiplexing
*one frequency - one message
E. Examples of hard-wired systems:
1. telegraph
2. telephone
3. some microphones
4. some intercom systems
F. Broadcast systems send radio waves through the air carrying the
signal from the sender to the receiver.
1. Sender changes sound into electrical wave containing message.
2. This signal radiates into the atmosphere from an antenna.
3. Another antenna attached to a receiver gathers the signal.
4. The receiver changes it back into audible sound.
G. The primary types of broadcast systems include:
1. radio broadcasting
a. carrier frequencies
*amplitude modulation (AM)
*frequency modulation (FM)
2. television systems
a. audio signal - frequency modulation
b. video signal - amplitude modulation
c. VHF (very high frequency) - channels 2 through 13
d. UHF (ultra high frequency) - channels 14 through 83
3. microwave systems
a. some telephone signals
b. satellite systems