298 and 14302 MHz In SSB only one side band is used Figure 3 17 a shows that

298 and 14302 mhz in ssb only one side band is used

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modulation would produce sidebands of 14.298 and 14.302 MHz. In SSB, only one side- band is used. Figure 3-17( a ) shows that only the upper sideband is generated. The RF signal is simply a constant-power 14.302-MHz sine wave. A time-domain display of this SSB signal is shown in Fig. 3-17( b ). Of course, most information signals transmitted by SSB are not pure sine waves. A more common modulation signal is voice, with its varying frequency and amplitude con- tent. The voice signal creates a complex RF SSB signal that varies in frequency and amplitude over the narrow spectrum defined by the voice signal bandwidth. The wave- form at the output of the SSB modulator has the same shape as the baseband waveform, but it is shifted in frequency. Disadvantages of DSB and SSB The main disadvantage of DSB and SSB signals is that they are harder to recover, or demodulate, at the receiver. Demodulation depends upon the carrier being present. If the carrier is not present, then it must be regenerated at the receiver and reinserted into the signal. To faithfully recover the intelligence signal, the reinserted carrier must have the same phase and frequency as those of the original carrier. This is a difficult requirement. When SSB is used for voice transmission, the reinserted carrier can be made variable in frequency so that it can be adjusted manually while listening to recover an intelligible signal. This is not possible with some kinds of data signals. Amplitude Modulation Fundamentals 111 Suppressed LSB Carrier USB SSB signal 14.298 14.3 14.302 Frequency (MHz) SSB signal 14.302-MHz sine wave ( a ) ( b ) Figure 3-17 An SSB signal produced by a 2-kHz sine wave modulating a 14.3-MHz sine wave carrier. Selective fading