Question

The role of envelope detector in an AM receiver is to

• A. retrieve the message signal
• B. rectify the AM signal
• C. modify the AM signal
• D. modulate the message signal
• E. retrieve the AM signal

Hint:

Envelope detector = demodulator → extracts message from AM wave.

Answer 1

The Correct Option is A

Concept: Amplitude Modulation (AM) and Demodulation
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Step 1: Understand AM signal structure
In AM (Amplitude Modulation):
• A high-frequency carrier wave is used
• The amplitude of the carrier is varied according to the message signal Mathematically: \[ \text{AM signal} = [A + m(t)] \cos(\omega t) \] where:
• $m(t)$ = message signal
• $\cos(\omega t)$ = carrier wave ---

Step 2: What happens at receiver
At the receiver:
• We receive the AM signal
• We need to extract $m(t)$ (original information) ---

Step 3: Role of envelope detector
Envelope detector:
• Tracks the outer shape (envelope) of the AM wave
• This envelope represents the message signal ---

Step 4: Working mechanism
It consists of:
• Diode → rectifies signal
• Capacitor + resistor → smoothens output Steps:
• Diode removes negative half cycles
• Capacitor charges to peak values
• Output follows envelope shape ---

Step 5: Important distinction

• Rectification is only a step
• Final goal = recover message signal ---

Step 6: Evaluate options

• (A) Correct → retrieves original signal ✔
• (B) Partial step only ❌
• (C) Wrong ❌
• (D) Opposite process ❌
• (E) Already available ❌ --- Final Answer: \[ \boxed{\text{Retrieve the message signal}} \]