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Flashcards in L5 Modulation Deck (39):
1

Communication systems

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

2

Communication systems

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

3

Input transducer

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

4

Transmitter:

The device that sends the transduced signal

5

Transmission channel:

The physical medium on which the signal is carried

6

Receiver:

The device that recovers the transmitted signal from the channel

7

Output transducer

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

8

The purpose of a communication system

transmit information signals (baseband signals) through a communication channel

9

baseband

a signal that has a very narrow frequency range.
the band of frequencies representing the original signal as delivered by the input transducer

10

Example of baseband signal

the voice signal from a microphone

11

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

0-3000 Hz

12

modulation

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

13

demodulation

shift back to the original frequency range after reception.

14

AM radio system transmits electromagnetic waves with frequencies of

around a few hundred kHz (MF band)

15

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

88-108 MHz (VHF band)

16

baseband signal contains frequencies in the audio frequency range

3 kHz

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

modulator

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

demodulator

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

carrier wave

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

Modulation

21

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

Modulation

22

Amplitude Modulation (AM)

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

23

Frequency Modulation (FM)

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

24

Types of analog modulation

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

25

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

Amplitude Shift Keying
Frequency Shift Keying
Phase Shift Keying

26

Amplitude Shift Keying (ASK)

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 .

27

Frequency Shift Keying (FSK)

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

28

how is ASK represented?

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

29

how is FSK represented?

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

30

Modems

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

31

The name modem comes from the name

MOulator- DEModulator

32

MOulator- DEModulator describes

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

33

The goal of modems is to

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

34

what are modems used for?

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

35

kinds of modems available

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

36

Internal modem

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

37

External modem

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

38

DSL (Digital Subscriber Line)

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

39

Cable modem

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