Analog Signals No. 1  Seattle Pacific University Band Limited Signals: Sending Analog Data with Band Limited Signals Based on Chapter 5 of William Stallings, Data and Computer Communication Kevin Bolding Electrical Engineering Seattle Pacific University

Analog Signals No. 2  Seattle Pacific University Pulse Trains vs. Band-Limited Signals Pulse Trains consume the entire bandwidth of the transmission medium Band-Limited signals are waves (compositions of sine waves) and constrained to a specified band of a medium’s bandwidth Line coding uses pulse trains to send digital data Band-limited signals may be used to send analog or digital data

Analog Signals No. 3  Seattle Pacific University Modulation Modulation is the process of combining a signal wave and a carrier wave Carrier wave has frequency f c, which must be greater than the modulating wave’s frequency, f m Modulation allows the engineer to move the base frequency of a band Allows the use of higher-frequency media Makes frequency-division multiplexing possible

Analog Signals No. 4  Seattle Pacific University Amplitude Modulation Generate a signal by modulating the amplitude of the carrier with the signal wave CarrierSignal Modulation Index

Analog Signals No. 5  Seattle Pacific University Multiplying Sine/Cosine Waves If the signal x(t) is a single cosine wave, we get (with a modulation index of 1): CarrierDifference Sum fcfc f c - f x f c + f x 0 pwr f Spectrum Analyzer view

Analog Signals No. 6  Seattle Pacific University AM Signal Spectrum Modulating signal covers a band from 0Hz to B Carrier signal is concentrated at F c Combined signal has bandwidth of 2B, centered at F c Includes a large amount of power at F c Sending just one sideband reduces the bandwidth to B Filtering out the carrier reduces the power required 0F c -B S(f) fFcFc F c +B Upper sideband Lower sideband 0B M(f) fFcFc SignalCarrier 0F c -B S(f) fFcFc F c +B Single Sideband Carrier F c Bandpass Filter (F c to F c +B) Signal BW: B

Analog Signals No. 7  Seattle Pacific University Power of an AM Signal Carrier Power Total Power Note: Largest practical modulation index is 1 Modulation Index

Analog Signals No. 8  Seattle Pacific University AM Detection To Detect (Demodulate) an AM Signal: V in V out Rectify it to remove the negative portion of the waveform Low pass filter using a simple RC filter

Analog Signals No. 9  Seattle Pacific University Frequency/Phase Modulation Generate a signal by modulating the frequency/phase of the carrier with the signal wave Angle OffsetCarrier For phase modulation: For frequency modulation: Carrier Signal

Analog Signals No. 10  Seattle Pacific University FM/PM Signal Spectrum FM/PM frequencies vary according to an analog signal Analog signal --> Unlimited precision Unlimited bandwidth needed Some practical limits Maximum frequency deviation  F is proportional to maximum amplitude in the modulating signal Carson’s rule for FM bandwidth requirement: works well