Analogue Modulation

Question 1

What are the two categories of analogue modulations?

Answer 1

AM (Amplitude modulation) and FM (frequency modulation)

Question 2

What are the three kinds of AM?

Answer 2

Simple Amplitude Modulation, DSB-SC (Double SideBand - Suppressed Carrier) and SSB-SC (Single SideBand - Suppressed Carrier)

Question 3

What is the power draw of each form of AM?

Answer 3

Simple AM: a₀²/2 + P_x/2

DSB-SC: P_x/2
SSB-SC: P_x/4

Question 4

How are FM signals decoded?

Answer 4

The signal goes through a differentiator (resulting in an amplitude modulated signal) and then an envelope detector is used

Question 5

What is an envelope detector?

Answer 5

An envelope detector is a very simple circuit used as a receiver. It is a diode, followed by a capacitor and resistor in parallel, creating a low pass filter. It removes the carrier frequency.

Question 6

What are the limits of an envelope detector?

Answer 6

Since it contains a diode, input signal must be entirely positive to avoid phase reversal, so modulation index (max X/a0) must be less than 1