EMS 4

Question 1

Define Signal

Answer 1

A detectable quantity or impulse by which messages or information can be transmitted over time.
Signals can by physical, electrical or electromagnetic.

Question 2

Describe the attributes of a periodic signal

Answer 2

A periodic signal repeats indefinitely.
* Attributes of a periodic signal that can be altered are : amplitude,
frequency and phase

Question 3

List the types of modulation

Answer 3

Amplitude Modulation (AM)
Frequency Modulation (FM)
Phase Modulation (PM)

Question 4

Describe Amplitude Modulation (AM)

Answer 4

The amplitude of a carrier is varied by the
modulating signal (intelligence).
The modulating signal is typically audio.
The difference between the USB and LSB is the bandwidth (BW)

Question 5

List the advantages and disadvantages of AM

Answer 5

AM is relatively simple
AM is inexpensive

Excessive Bandwidth
– Each AM waveform sideband contains identical intelligence.
– Only one sideband need be transmitted.
Waste of Power
– 2/3 of the power is contained in the carrier of an AM waveform.

Question 6

List the types of AM enhancements

Answer 6

No reason to transmit the carrier.
* Options leading to single sideband transmission:
– Double Sideband Full Carrier (AM),
– Double Sideband Reduced Carrier (DSBRC)
– Double Sideband Suppressed Carrier (DSBSC)
– Single Sideband (SSB)

Question 7

Describe Frequency Modulation (FM)

Answer 7

The frequency of a carrier is varied by the
modulating signal (intelligence).
The modulating signal is typically the data.

Question 8

List the advantages and disadvantages of FM

Answer 8

Noise immunity

Large BW required.
More complex equipment .

Question 9

Explain FM noise immunity

Answer 9

Electrical noise consists of any voltage (amplitude) change that interferes with the operation of an electrical system
Due to FM transmissions relying on frequency change and not amplitude change (AM), FM transmissions are
said to have Noise Immunity.

Question 10

Describe multiplexing methods

Answer 10

Analogue signals:
* Frequency Division Multiplexing (FDM)
* Wavelength Division Multiplexing (WDM)
Digital Signals:
* Time Division Multiplexing (TDM)
Analogue and Digital signals:
* Code Division Multiple Access (CDMA)

Question 11

Describe the various types of modulation on signals and their uses.

Answer 11

FM radio and music: Frequency modulation is widely used in radio broadcasting. It is a wideband FM, and its frequency is much larger than that of AM. Due to its low radio frequency interference, it is preferred to use FM to broadcast music on the radio.
* Television sound: The video information in a television broadcast is transmitted using AM, while FM is used for sound transmission due to low interference.
* Satellite TV: Some satellites use FM to broadcast video signals on the receiver’s station.

Question 12

Explain the need for modulation

Answer 12

Modulation is the process of placing intelligence onto a carrier frequency.
Modulation allows practical antenna transmit/receive hardware to
pass intelligence over large distances.

Question 13

Describe Multiplexing

Answer 13

Enables transmission of multiple signals through a single shared communication channel.
* Takes multiple signals and combines them into one signal that is transmitted over a shared communication channel.