Single sideband

Chapter Single sideband

Teach Yourself Electricity and Electronics Third Edition Book
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Summary of Contents

Teach Yourself Electricity and Electronics Third Edition Book

  • In an AM signal, the bandwidth is twice the highest audio modulating frequency. Inthe example of Fig. 26-7, the voice energy is all below 3 kHz, and the bandwidth of thecomplete RF signal is 6 kHz. At 3 kHz above and below the carrier, the frequency cut-offs are abrupt. This transmitter uses an audio lowpass filter that cuts out the audioabove 3 kHz. Audio above 3 kHz contributes nothing to the intelligibility of a humanvoice. It’s important to keep the bandwidth of a signal as narrow as possible, so therewill be room for many signals in a given band of frequencies.Single sidebandAs mentioned previously, AM is not efficient. Most of the power is used up by the car-rier; only 33 percent of it carries data. Besides that, the two sidebands are mirror-imageduplicates. An AM signal is redundant, as well as inefficient, for voice transmission.480 Data transmission26-6At A, transmitter using low-level AM. At B, a transmitter using high-level AM.