INTRODUCTION TO ANALOG COMMUNICATION(Chapter 1)

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Elements of a Communication System Communication involves the transfer of information or intelligence from a source to a recipient via a channel or medium.

Basic block diagram of a communication system:

Source Transmitter Receiver Recipient

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Brief Description

Source: analog or digital Transmitter: transducer, amplifier, modulator,

oscillator, power amp., antenna Channel: e.g. cable, optical fiber, free space Receiver: antenna, amplifier, demodulator,

oscillator, power amplifier, transducer Recipient: e.g. person, speaker, computer

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Frequency Bands

BAND Hz

4 ELF 30 - 300

4 AF 300 - 3 k

4 VLF 3 k - 30 k

4 LF 30 k - 300 k

4 MF 300 k - 3 M

4 HF 3 M - 30 M

BAND Hz

4 VHF 30M-300M

4 UHF 300M - 3 G

4 SHF 3 G - 30 G

4 EHF 30 G - 300G

•Wavelength, l = c/f

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Information and Bandwidth

Bandwidth required by a modulated signal depends on the baseband frequency range (or data rate) and the modulation scheme.

Hartley’s Law: I = k t Bwhere I = amount of information; k = system constant; t = time available; B = channel bandwidth

Shannon’s Formula: I = B log2 (1+ S/N) in bps

where S/N = signal-to-noise power ratio

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Transmission Modes

Simplex (SX) – one direction only, e.g. TV Half Duplex (HDX) – both directions but not at

the same time, e.g. CB radio Full Duplex (FDX) – transmit and receive

simultaneously between two stations, e.g. standard telephone system

Full/Full Duplex (F/FDX) - transmit and receive simultaneously but not necessarily just between two stations, e.g. data communications circuits

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Time and Frequency Domains Time domain: an oscilloscope displays the

amplitude versus time Frequency domain: a spectrum analyzer displays

the amplitude or power versus frequency Frequency-domain display provides information on

bandwidth and harmonic components of a signal

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Non-sinusoidal Waveform

Any well-behaved periodic waveform can be represented as a series of sine and/or cosine waves plus (sometimes) a dc offset:

e(t)=Co+SAn cos n w t + SBn sin nw t (Fourier series)