**Simplex**

**—**One direction

• e.g. Television

**Half duplex**

— Either direction, but only one way at a time

• e.g. police radio

**• Full duplex**

— Both directions at the same time

• e.g. telephone

**Frequency, Spectrum and**

**Bandwidth**

**Time domain concepts**

Analog signal

• Varies in a smooth way over time

— Digital signal

• Maintains a constant level then changes to another constant

level

— Periodic signal

• Pattern repeated over time

— Aperiodic signal

• Pattern not repeated over time

**Analogue & Digital Signals**

Periodic

Signals

__Frequency Domain Concepts__

Signal is usually made up of many frequencies

• Components are sine waves

• It can be shown (Fourier analysis) that any

signal is made up of component sine waves

• One can plot frequency domain functions

**Data Rate and Bandwidth**

**• Any transmission system has a limited band of**

**frequencies**

**• This limits the data rate that can be carried**

**Reference :-**

# Data Communication

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