Appendix Analog ContinuousWave CW Modulation Appendix 1 Analog

Appendix: Analog Continuous-Wave (CW) Modulation Appendix 1

Analog CW Modulation: Definition Appendix 2

Analog CW Modulation: Types Modulator Appendix Demodulator 3

Continuous-Wave Modulation (a) Sinusoidal modulating signal (b) Carrier wave (c) Amplitude modulated signal Appendix (d) Phase modulated signal (e) Frequency modulated signal 4

Conventional (DSB-PC) Amplitude Modulation Appendix 5

DSB-PC AM Spectrum (a) Modulating signal Appendix 6

DSB-PC-AM Envelope (a) Modulating signal (b) Envelope is always positive (c) Envelope is not always positive Appendix 7

DSB-PC Amplitude Modulation: Switching Modulator (a) Switching modulator (b) Ideal diode input-output characteristic graph (c) Periodic pulse train Appendix 8

DSB-PC Amplitude Demodulation: Envelope Detection Appendix 9

DSB-SC Amplitude Modulation Modulating signal Modulated signal Appendix 10

Balanced Modulator and Coherent Detection for DBS-SC AM DSB-AM modulator Product modulator LPF Oscillator DSB-AM modulator Appendix Oscillator 11

SSB-SC AM Product modulator Bandpass filter Oscillator Modulating signal Modulator Product modulator Lowpass filter SSB-SC AM (USB) Oscillator Coherent demodulator SSB-SC AM (LSB) Appendix 12

VSB-SC AM Product modulator Oscillator Product modulator Lowpass filter Oscillator Appendix 13

Frequency Modulation Appendix 14

FM Bandwidth Appendix 15

FM Modulator Integrator Product modulator Oscillator NB FM NBFM modulator Product modulator BPF Oscillator WB FM Appendix 16

FM Demodulation Frequency response of ideal slope circuit Envelope detector Frequency discriminator Appendix 17

Preemphasis and Deemphasis in an FM System AWGN Preemphasis filter FM transmitter FM receiver Deemphasis filter Preemphasis filter characteristics Deemphasis filter characteristics Appendix 18

Block Diagram of an AM Superheterodyne Receiver Speaker Antenna Frequency converter (mixer) Common tuning (by a knob) Appendix Envelope detector Audio amplifier Automatic volume control 19

Image Interference (a) Desired signal Image signal (b) Appendix 20

Block Diagram of an FM Superheterodyne Receiver Antenna Speaker Frequency converter (mixer) Common tuning (by a knob) Appendix Lowpass filter Audio amplifier & de-emphasis Amplitude limiter Frequency discriminator Automatic frequency control 21

FM Stereo Broadcasting Preemphasis LHS signal RHS signal Frequency doubler Pilot tone FM modulator Preemphasis (a) FM stereo transmitter Lowpass filter FM discriminator Composite baseband spectrum Narrowband filter Bandpass filter Pilot tone Deemphasis Audio amplifier Frequency doubler (c) FM stereo receiver (b) Spectrum of FM stereo signal Appendix 22

Comparison of Analog CW Modulation Schemes Implementation – When the carrier wave in AM is transmitted, a simple receiver employing envelope detection can be employed. However, the transmission of the carrier wave represents a significant waste of power. A system, in which the carrier wave is suppressed, such as DSB-SC AM, SSB-SC AM, and VSB-SC AM, requires synchronous demodulation. Also, FM receivers widely used in high-fidelity radio broadcasting (with FM stereo) are rather easy to implement Bandwidth – A system employing a linear modulation (e. g. , DSB, VSB, SSB), with or without a carrier wave, requires a bandwidth that is a small fraction of what is required for an angle modulation. In AM radio broadcasting, the channel spacing is a mere 10 k. Hz, but in FM radio broadcasting, it is 200 k. Hz. The generous use of bandwidth in FM brings about a high degree of immunity to noise. Power – In a system employing an amplitude modulation scheme, the signal-to-noise ratio at the receiver output can be increased only by increasing the transmitted signal power. Unlike an AM system, the transmitted power in an FM system is completely independent of the modulating signal. Nonlinearity – Amplitude modulation is highly sensitive to amplitude nonlinearity in the communication channel, whereas frequency modulation is fundamentally unaffected by such nonlinearity. Frequency modulation is, however, quite sensitive to phase nonlinearity, such as AM-to-PM conversion experienced in radio channels. Appendix 23