Studieboek C - Review questions
3 important questions on Studieboek C - Review questions
Sketch the circuit for an AM diode envelope detector and briefly explain how it works
The diode conducts on positive half-cycles of the AM signal, charging C1 rapidly toward the peak envelope value. Between peaks C1 discharges through R1. The RC time constant is chosen so that 1
fc ≪ R1C1 ≪ 1/W : the carrier ripple is filtered out while the audio envelope is faithfully tracked.
List two methods used for generating SSB
1. Filter method: generate DSB-SC and pass it through a highly selective band-pass filter to retain only one sideband.
2. Phase-shift method: apply 90° phase shifts to both the carrier and the message signal; one sideband cancels when the two branches are summed
What happens to the recovered message in a coherent DSB-SC demodulator if there is a small frequency error ∆f between the transmitter carrier and the receiver local oscillator?
If the local oscillator is at fc + ∆f instead of fc, the demodulated signal is m(t) multiplied by cos(2π∆f t). This produces a slow amplitude variation at frequency ∆f . For voice, even a few Hz of offset produces an unpleasant warbling effect; the speech becomes unintelligible for offsets of tens of H
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