L5 Modulation

Question 1

Communication systems

Answer 1

1- Analog Modulation:
AM and FM
2-Digital Modulation
ASK and; FSK
3- Modems

Question 2

Communication systems

Answer 2

1- Input Transducer
2- Transmitter
3- Transmission channel
4- Receiver
5- Output transducer

Question 3

Input transducer

Answer 3

The device that converts a physical signal from source to an electrical, mechanical or electromagnetic signal more suitable for communicating

Question 4

Transmitter:

Answer 4

The device that sends the transduced signal

Question 5

Transmission channel:

Answer 5

The physical medium on which the signal is carried

Question 6

Receiver:

Answer 6

The device that recovers the transmitted signal from the channel

Question 7

Output transducer

Answer 7

The device that converts the received signal back into a useful quantity

Question 8

The purpose of a communication system

Answer 8

transmit information signals (baseband signals) through a communication channel

Question 9

baseband

Answer 9

a signal that has a very narrow frequency range.

the band of frequencies representing the original signal as delivered by the input transducer

Question 10

Example of baseband signal

Answer 10

the voice signal from a microphone

Question 11

The voice signal from a microphone contains frequencies in the range of

Answer 11

0-3000 Hz

Question 12

modulation

Answer 12

a procedure that shifts the range of baseband frequencies to other frequency ranges suitable for transmission

Question 13

demodulation

Answer 13

shift back to the original frequency range after reception.

Question 14

AM radio system transmits electromagnetic waves with frequencies of

Answer 14

around a few hundred kHz (MF band)

Question 15

The FM radio system must operate with frequencies in the range of

Answer 15

88-108 MHz (VHF band)

Question 16

baseband signal contains frequencies in the audio frequency range

Answer 16

3 kHz

Question 17

The transmitter block in any communications system contains the …………….. device

Answer 17

modulator

Question 18

The receiver block in any communications system contains the ………………… device

Answer 18

demodulator

Question 19

The modulator modulates a …………………………….

Answer 19

carrier wave

Question 20

…………………….. is the process of impressing a low-frequency information signal (baseband signal )onto a higher frequency carrier signal

Answer 20

Modulation

Question 21

……………………….is done to bring information signals up to the Radio Frequency (or higher) signal

Answer 21

Modulation

Question 22

Amplitude Modulation (AM)

Answer 22

Amplitude modulation is the process of varying the amplitude of a carrier wave in proportion to the amplitude of a baseband signal. The frequency of the carrier remains constant

Question 23

Frequency Modulation (FM)

Answer 23

Frequency modulation is the process of varying the frequency of a carrier wave in proportion to the amplitude of a baseband signal. The amplitude of the carrier remains constant

Question 24

Types of analog modulation

Answer 24

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

Question 25

Digital communication systems also employ modulation techniques, some of which include:

Answer 25

Amplitude Shift Keying Frequency Shift Keying Phase Shift Keying

Question 26

Amplitude Shift Keying (ASK)

Answer 26

involves the process of switching the carrier either on or off, in correspondence to a sequence of digital pulses that constitute the information signal. Frequency remains fixed .

Question 27

Frequency Shift Keying (FSK)

Answer 27

involves the process of varying the frequency of a carrier wave by choosing one of two frequencies (binary FSK) in correspondence to a sequence of digital pulses that constitute the information signal. Amplitude remains fixed

Question 28

how is ASK represented?

Answer 28

One binary digit is represented by the presence of a carrier, the other binary digit is represented by the absence of a carrier.

Question 29

how is FSK represented?

Answer 29

Two binary digits are represented by two frequencies around the carrier frequency.

Question 30

Modems

Answer 30

devices used to enable the transfer of data over the public switched telephone network (PSTN)

Question 31

The name modem comes from the name

Answer 31

MOulator- DEModulator

Question 32

MOulator- DEModulator describes

Answer 32

describes the function the modem performs to transfer digital information over an analog network

Question 33

The goal of modems is to

Answer 33

produce a signal that can be transmitted easily and decoded to reproduce the original digital data.

Question 34

what are modems used for?

Answer 34

communicate via telephone lines, modems can be used over any means of transmitting analog signals

Question 35

kinds of modems available

Answer 35

1- Internal modem 2- external modem 3- DSL (Digital Subscriber line) 4- cable modem

Question 36

Internal modem

Answer 36

A modem card in your computer that is integrated within the system Less expensive than external modems Disadvantage is that you need to access inside the computer to replace the modem

Question 37

External modem

Answer 37

A device that connects externally to your computer through a serial port External power supply does not drain power from the computer Modem activity can easily be observed More expensive than an internal modem

Question 38

DSL (Digital Subscriber Line)

Answer 38

A high-speed data service that works over conventional telephone lines and is typically offered by telephone companies It does not occupy the phone line-you can still talk on the phone Speed is much higher than regular modem

Question 39

Cable modem

Answer 39

A device that connects to the existing cable feed and to an Ethernet network card in the PC (also called a NIC for Network Interface Card) Is different than a common dial up modem Supports higher speeds Typically offered by cable companies