Communication Systems: Why Noise Sets the Speed Limit
From AM radio to Wi-Fi, the surprising rules that decide how much information can cross a noisy channel.
Communication Systems · 50 questions
Try 3 questions
1. In standard AM at 100% modulation, roughly what share of the transmitted power sits in the carrier?
- About one third
- About two thirds
- About one half
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Answer: About two thirds
With full modulation the two sidebands together carry half the carrier's power, so the carrier holds 1 of 1.5 units: two thirds.
2. An AM transmitter is modulated by a pure 5 kHz tone. How much bandwidth does the double-sideband signal occupy?
- 10 kHz
- 2.5 kHz
- 5 kHz
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Answer: 10 kHz
Sidebands appear 5 kHz above and 5 kHz below the carrier, so the signal spans twice the highest audio frequency.
3. Why can a cheap envelope detector demodulate standard AM but not suppressed-carrier DSB?
- The carrier keeps the envelope tracing the message
- DSB-SC signals always use a much higher frequency
- DSB-SC places the audio in only one sideband
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Answer: The carrier keeps the envelope tracing the message
Without the large carrier, the envelope follows the absolute value of the message and crosses zero, so the audio is distorted.
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