1.6 Analogue Modulation

Question 1

What is amplitude modulation?

Answer 1

Question 2

What is the Modulation Index?

Answer 2

For m = 0.5, the carrier amplitude varies by 50% above and below its modulated level.

Question 3

What is Over Modulation?

Answer 3

Distortion caused by carrier phase inversion.

Question 4

Answer 4

Question 5

What is DSB-FC?

Answer 5

Double Side Band- Full Carrier

Simple receiver design, inexpensive.

Transmits twice the required bandwidth.
Power is also wasted, 66% of the power is wasted in the carrier.

Question 6

What is DSB-SC? What are Pro’s and Con’s?

Answer 6

Dual Side Band - Suppressed Carrier

Greater percentage of the power is transmitted in the sidebands

Complex receiver.

A local oscillator must be synchronized in frequency and phase with the original carrier signal to be coherent.

Question 7

What is SSB-SC?

Answer 7

Single Side Band - Suppressed Carrier

Removing one of the sidebands. This is most commonly done by filtering out one of the sidebands.

This is ideal for long distance communications where bandwidth is limited.

Question 8

What is VSB-SC

Answer 8

Vestigial Side Band - Suppressed Carrier

We only reduce part of one of the sidebands IOT conserve bandwidth.

Question 9

What is Transmission Efficiency?

Answer 9

Fraction of total power contained in the sidebands. Can be expressed as a percentage directly related to the modulation index.

Question 10

Is AM susceptible to noise? Why?

Answer 10

AM is very susceptible to noise because information is carried in the amplitude. Noise and interferference can directly affect the amplitude of the signal.