Lecture02 Spring04

Electrical Network IS AN INTERCONNECTION
OF ELECTRICAL COMPONENTS

L
R1
vS



R2 vO


+
-

C
TYPICAL
LINEAR
CIRCUIT

OBJECTIVES
• To analyze, design and measure a number of quantities (e.g. current, voltage) of linear analog electrical network systems, across engineering disciplines and within sub-disciplines of
Electrical Engineering.

EE Subdisciplines
• Power
• Electromagnetics
• Communication/
Signal Processing
• Digital
• Controls
• Solid State

The AM Radio
&
The Telephone System

The AM Radio
• Understanding the AM radio requires knowledge of several EE subdisciplines:
– Communications/signal processing (frequency domain analysis)
– Electromagnetics (antennas, high-frequency circuits) – Power (batteries, power supplies)
– Solid state (miniaturization, low-power electronics) The AM Radio “System”

Transmitter

Receiver

Signal
• The radio system can be understood in terms of its effect on signals.
• A signal is a quantity that may vary with time.
– Voltage or current in a circuit
– Sound (pressure wave traveling through air)
– Light or radio waves (electromagnetic energy traveling through free space)

Frequency
• The analysis and design of AM radios (and communication systems in general) is usually conducted in the frequency domain using
Fourier analysis.
• Fourier analysis allows us to represent signals as combinations of sinusoids (sines and cosines). Frequency
Frequency is the rate at which a signal oscillates. High Frequency

Low Frequency

Sound Waves
• Sound is a pressure wave in a transmission medium such as air or water.
• We perceive the frequency of the wave as the “pitch” of the sound.
• A single frequency sound sounds like a clear whistle.
• Noise (static) is sound with many frequencies. Fourier Analysis
• Mathematical analysis of signals in terms of frequency
• Most commonly encountered signals can be represented as a Fourier series or a
Fourier transform.
• A Fourier series is a weighted sum of cosines and sines.

Example-Fourier