Book 4

Question 1

List advantages of using digital modulation

Answer 1

Easier to encrypt

Easier to update systems

Multiplexing can be used

Less vulnerable to noise and static

Question 2

In pulse coded modulation what is meant by quantisation error

Answer 2

Difference between the measured amplitude and digital code

Question 3

How is quantisation error reduced

Answer 3

Using more digital levels

Question 4

In pulse coded modulation what is meant by aliasing

Answer 4

Production of ghost signals

Question 5

How is aliasing reduced

Answer 5

Higher sampling rate

Question 6

Advantages of multiplexing

Answer 6

Allows many signals to be transmitted on one Channel

Allows Sharing a given bandwidth between several signal sources

Question 7

Describe time division multiplexing

Answer 7

Each channel assigned a time slot

Question 8

Describe frequency division multiplexing

Answer 8

Bandwidth divided into different frequencies

Question 9

Describe code division multiplexing

Answer 9

Each signal is given a different code

Question 10

Disadvantage of digital modulation

Answer 10

Much greater bandwidth needed

Question 11

Explain Frequency Hopping Spread Spectrum

Answer 11

The transmitted bandwidth is wider than the bandwidth of the modulating signal

This is achieved by another signal