Network

Electronic TransmissionTransmitter

The transmitter itself is a collection of electronic components and circuits designed to convert the electrical signal to a signal suitable for transmission over a given communication medium. Transmitters are made up of oscillators, amplifiers, tuned circuits and filters, modulators, frequency mixers, frequency synthesizers, and other circuits.

Communication Channel

• Electrical Conductors: In its simplest form, the medium may simply be a pair of wires that carry a voice signal from a microphone to a headset. It may be a coaxial cable such as that used to carry cable TV signals. Or it may be a twisted-pair cable used in a local-area network (LAN).
• Optical Media: The communication medium may also be a fiber-optic cable or “light pipe” that carries the message on a light wave. These are widely used today to carry long-distance calls and all Internet communications. The information is converted to digi- tal form that can be used to turn a laser diode off and on at high speeds. Alternatively, audio or video analog signals can be used to vary the amplitude of the light.
• Free Space: When free space is the medium, the resulting system is known as radio. Also knownas wireless, radiois the broad general term applied to any form of wireless communication from one point to another. Radio makes use of the electromagnetic spec- trum. Intelligence signals are converted to electric and magnetic fields that propagate nearly instantaneously through space over long distances.

Receivers

A receiver is a collection of electronic components and circuits that accepts the transmitted message from the channel and converts it back to a form understandable by humans.

Note that, most electronic communication is two-way, and so both parties must have both a transmitter and a receiver. As a result, most communication equipment incorporates circuits that both send and receive. These units are commonly referred to as transceivers.

Noise

Noise is mentioned here because it is the bane of all electronic communications. Its effect is experienced in the receiver part of any communications system. For that reason, we cover noise at that more appropriate time in Chapter 9. While some noise can befiltered out, the general way to minimize noise is to use components that contribute less noise and to lower their temperatures. The measure of noise is usually expressed in terms of the signal-to-noise (S/N) ratio (SNR), which is the signal power divided by the noise power and can be stated numerically or in terms of decibels (dB). Obviously, a very high SNR is preferred for best performance.

Types of Electronic Communications

Simplex// half duplex // full duplex

note that, why use half duplex? Mostly legacy. Some equipment (especially in 10Base-T days) is only capable of half-duplex operation. These days I usually assume full duplex unless I see collisions/errors on the interface, etc.

Modulation and Multiplexing

Modulation and multiplexing are electronic techniques for transmitting information efficiently from one place to another. Modulation makes the information signal more compatible with the medium, andmultiplexingallows more than one signal to be trans- mitted concurrently over a single medium. Modulation and multiplexing techniques are basic to electronic communication.

Baseband Transmission

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