Bandpass Signaling

Bandpass Signaling

The bandpass communication signal is obtained by modulating a baseband analog or digital signal. We will use complex envelopes because with them we can represent any type of banppass signal.

Definitions: Baseband, Bandpass, and Modulation

DEFINITION. A baseband waveform has a spectral magnitude that is nonzero for frequencies in the vicinity of the origin (i.e., f = 0) and negligible elsewhere.

DEFINITION. A bandpass waveform has a spectral magnitude that is nonzero for frequencies in some band concentrated about a frequency cff where cf . > 0. The spectral magnitude is negligible elsewhere. cf is called the carrier frequency.

DEFINITION. Modulation is the process of imparting the source information onto a bandpass signal with a carrier frequency cf by the introduction of amplitude or phase perturbations or both. This bandpass signal is called the modulated signal s(t), and the baseband source signal is called the modulating signal m(t).

Bandpass Signaling.

Representation of Modulated Signals

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)]([)( tmgtg

Spectrum of Bandpass Signals

22 )(21

)( tgtvPv

Spectrum of Bandpass Signals

Bandpass Filtering and Linear Distortion

Bandpass Filtering and Linear Distortion

AM Modulation

Amplitude Modulated Signal

AM Modulation

Spectrum

Peak Envelope Power

AM Modulation

Low Level AM Modulation

Low Level AM Modulation

AM Detection

High Level AM Modulation

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Can you use envelope detector in DSB ?

AM Modulation

Double Side Band Suppresed Carrier

ttmAtscc cos)()(

Efficiency

cc

c ffMffMA

fS )(2

)(

DSB Modulation

AM Modulation

PLL

Double Side Band Suppresed Carrier receivers

Single Sideband

ASYMMETRIC SIDEBAND SIGNALS Single SideBand

Bandpass Signaling

SOME FOURIER TRANSFORM PAIRS

Single Sideband

Single Sideband Transmitters

Remember, we are using s(t) =v(t)

Single Sideband Transmitters

Vestigial Sideband

Vestigial Sideband