Engineer's Knowledge

Sine Wave in Frequency Domain

2013-03-15T10:42:00.000-07:00

A complete sine wave in the time domain can be represented by one single spike in the frequency domain.

The time-domain and frequency-domain plots of a sine wave

A single-frequency sine wave is not useful in data communication. We need to send a composite signal, a signal composed of many simple sine waves.

According to Fourier analysis, any composite signal is a combination of simple sine waves with different frequencies, amplitudes and phases.

A composite periodic signal

Decomposition of a composite periodic signal in the time and frequency domain

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Information about Frequency and Phase

2013-03-14T07:21:00.002-07:00

Units of Period and frequency

Frequency:

Frequency is the rate of change with respect to time.

Change in a short span of time means high frequency.

Change over a long span of time means low frequency.

The power we use at home has a frequency of 50-60 Hz.

If a signal does not change at all, its frequency is zero.

If a signal changes instantaneously, its frequency is infinite.

Phase

Phase describes the position of the waveform relative to time 0.

Fig.a shows a phase shift of 0 degrees.

Fig.b shows a phase shift of 90 degrees.

Fig.c shows a phase shift of 180 degrees.

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Periodic Analog Signals

2013-03-08T04:18:00.003-08:00

Periodic analog signals can be classified as simple or composite. A simple periodic analog signal, a sine wave, cannot be decomposed into simpler signals. A composite periodic analog signal is composed of multiple sine waves.

Topics discussed in this section:

Sine Wave
Wavelength
Time and Frequency Domain
Composite Signals

Bandwidth

Note:

In data communications, we commonly use periodic analog signals and non-periodic digital signals.

A sine wave

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Analog and Digital Data, Analog and Digital Signals

2013-03-07T07:21:00.001-08:00

Data can be analog or digital.

The term analog data refers to information that is continuous and digital data refers to the information that has discrete states.

Analog data take on continuous values and digital data take on discrete values.

Signals can be analog or digital.

Analog signals can have an infinite number of values in a range and digital signals can have only a limited

number of values.

Comparison of Analog and Digital Signals

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Sine Wave

2012-09-03T05:31:00.000-07:00

Peak Amplitude

Maximum strength of signal.

Volts.
Frequency

Rate of change of signal.

Hertz (Hz) or cycles per second.

Period = Time for one repetition (T)

T=1/f
Phase

Relative position in time.

Varying Sine Waves

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© Copyright Sajid Baloch

Components of Analog Signals

2012-09-02T05:07:00.004-07:00

Amplitude

The amplitude of a signal is the height of the wave above or below a given reference point.
Frequency

Frequency is the number of times a signal makes a complete cycle within a given time frame.

Spectrum: The range of frequencies that a signal spans from minimum to maximum.

Bandwidth: The absolute value of the difference between the lowest and highest frequencies of a signal

Example:-
The average voice has a frequency range of roughly 300 Hz to 3100 Hz.

The spectrum would thus be 300 - 3100 Hz.

The bandwidth would be 2800 Hz.
Phase

The phase of a signal is the position of the waveform relative to a given moment of time or relative to time zero. A change in phase can be any number of angles between 0 and 360 degrees. Phase changes often occur on common angles, such as 45, 90, 135, etc.

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© Copyright Sajid Baloch

Time Domain Concepts

2012-09-02T01:20:00.003-07:00

Continuous Signal

Various in a smooth way over time. e.g. speed.
Discrete Signal

Maintain a constant level then changes to another constant level. e.g. binary 1's and 0's.
Periodic Signal

Pattern repeated over time

Terminology

2012-09-01T11:01:00.000-07:00

Transmitter
Receiver
Medium

Guided Medium: Media in which signal is guided along a physical path. e.g. twisted pair, coax, optical fiber.

Unguided Medium: Media in which signal is not guided. e.g. air, water, vacuum.
Direct Link

No intermediate devices

Point to Point

Direct Link

Only 2 devices share link

Multi-point

More than two devices share link

Simplex

One Direction. e.g. Television

Half Duplex

Either Direction, but only one way at a time. e.g. Police radio

Data and Signals

2012-09-01T10:31:00.000-07:00

What is DATA and SIGNALS?

•Data are entities that convey meaning

•Signals are the electric or electromagnetic encoding of data

•Computer networks and data/voice communication systems transmit signals

•Data and signals can be analog or digital

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Engineer's Knowledge

Sine Wave in Frequency Domain

Information about Frequency and Phase

Periodic Analog Signals

Analog and Digital Data, Analog and Digital Signals

Sine Wave

Peak Amplitude

Maximum strength of signal.

Volts.

Frequency

Rate of change of signal.

Hertz (Hz) or cycles per second.

Period = Time for one repetition (T)

T=1/f

Phase

Relative position in time.

Varying Sine Waves

Components of Analog Signals

Amplitude

The amplitude of a signal is the height of the wave above or below a given reference point.

Frequency

Frequency is the number of times a signal makes a complete cycle within a given time frame.

Spectrum: The range of frequencies that a signal spans from minimum to maximum.

Bandwidth: The absolute value of the difference between the lowest and highest frequencies of a signal

Example:-The average voice has a frequency range of roughly 300 Hz to 3100 Hz.

The spectrum would thus be 300 - 3100 Hz.

The bandwidth would be 2800 Hz.

Phase

The phase of a signal is the position of the waveform relative to a given moment of time or relative to time zero. A change in phase can be any number of angles between 0 and 360 degrees. Phase changes often occur on common angles, such as 45, 90, 135, etc.

Time Domain Concepts

Continuous Signal

Various in a smooth way over time. e.g. speed.

Discrete Signal

Maintain a constant level then changes to another constant level. e.g. binary 1's and 0's.

Periodic Signal

Pattern repeated over time

Aperiodic Signal

Pattern not repeated over time

Terminology

Transmitter

Receiver

Medium

Guided Medium: Media in which signal is guided along a physical path. e.g. twisted pair, coax, optical fiber.

Unguided Medium: Media in which signal is not guided. e.g. air, water, vacuum.

Direct Link

No intermediate devices

Point to Point

Direct Link

Only 2 devices share link

Multi-point

More than two devices share link

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

Data and Signals

Example:-
The average voice has a frequency range of roughly 300 Hz to 3100 Hz.