Concept Flashcards

Concept Flashcards#

1. What is demodulation?

The process of recovering the original message signal from a modulated carrier.

2. What is AM efficiency?
\[ \eta = \frac{P_{USB} + P_{LSB}}{P_{total}} \]
3. What is the simplified AM efficiency equation?
\[ \eta = \frac{\alpha^2}{\alpha^2 + 2} \]
4. What is the efficiency of DSB-SC?
\[ \eta = 100\% \]
5. What is the efficiency when the modulation index is one (1)?
\[ \eta = 0.33 \ (33\%) \]
6. What is an envelope detector?

A circuit that recovers the message signal by tracking the envelope of an AM signal.

7. What are the three components of an envelope detector?

  • Diode

  • Low-pass filter (LPF)

  • High-pass filter (HPF)

8. What does the diode do in an envelope detector?

Removes the negative portion of the signal (rectification).

9. What does the LPF do in an envelope detector?

Removes the high-frequency carrier.

10. What does the HPF do in an envelope detector?

Removes the DC bias (0 Hz component).

11. When does an envelope detector work?

Only for under-modulated or 100%-modulated signals.

12. When does an envelope detector fail?

  • Over-modulated signals

  • DSB-SC signals

13. What is a synchronous detector?

A demodulator that multiplies the AM signal by the carrier to shift it back to baseband.

14. What are the components of a synchronous detector?

  • Function multiplier

  • Low-pass filter

  • High-pass filter

15. What are the key design rules for demodulators?

  • \(f_{demod} = f_c\)

  • \(f_{LPF} \ge f_{m,\ max}\)

  • \(f_{HPF} > 0\ \text{Hz}\) (typically 10 Hz)