lecture 6 data&signals

Question 1

data can be either

Answer 1

analog or digital

Question 2

analog data

Answer 2

the information is continuous and takes continuous values

Question 3

digital data

Answer 3

the information is discontinuous, has discrete states and takes discrete values

Question 4

examples of analog data

Answer 4

• a clock with moving minute/hour hands

- sound of human voice

Question 5

examples of digital data

Answer 5

• a digital clock (goes from 8:05 to 8:06)
• WhatsApp message
• email

Question 6

what is meant by discrete values

Answer 6

• stored on the computer in the form of 0’s and 1’s

Question 7

signals can be either

Answer 7

analog or digital

Question 8

analog signal

Answer 8

has an infinite number of values in a range

Question 9

digital signal range and levels

Answer 9

• has a limited number of defined values in a range

- can have more than two levels

Question 10

what is periodic analog signal

Answer 10

• a signal which completes a pattern within a period of time

- repeats that pattern over subsequent identical periods

Question 11

non-periodic digital signal

Answer 11

• a signal that changes without exhibiting a pattern or repetitiveness

Question 12

periodic analog signal can be classified as

Answer 12

• simple or composite

Question 13

simple periodic analog signal consists of:

Answer 13

one sine wave, and it cannot be decomposed into smaller signals

Question 14

composite periodic analog signal:

Answer 14

it is composed of various sine waves (combination)

Question 15

peak value=

Answer 15

sqrt2 x root mean square value (rms)

Question 16

period(s)=

Answer 16

T=1/F (inverse of frequency)

Question 17

frequency(Hz)=

Answer 17

F=1/T (inverse of period)

Question 18

peak value is called

Answer 18

the amplitude

Question 19

frequency refers to

Answer 19

how many cycles (oscillations) per second

Question 20

period refers to

Answer 20

the time taken for one cycle (oscillation)

Question 21

frequency and change

Answer 21

1. change over a short period of time = higher frequency
2. change over a long period of time = lower frequency
3. no change = frequency equals zero

Question 22

phase shift

Answer 22

how much you shifted from time 0

Question 23

radians=

Answer 23

degrees * pi/180

Question 24

a cycle represents

Answer 24

2 pi’s and 360 degrees

Question 25

frequency and wavelength

Answer 25

1. the higher the frequency, the smaller the wavelength | 2. the lower the frequency, the bigger the wavelength

Question 26

frequency domain represents

Answer 26

a periodic sine wave using a single vertical line

Question 27

why is a single frequency sine wave not | useful in data communications?

Answer 27

because we need to send a composite signal, which is a combination of sine waves of different frequencies, amplitudes and phases

Question 28

If the composite signal is periodic, the | decomposition gives

Answer 28

a series of signals with discrete frequencies

Question 29

if the composite signal is non-periodic, | the decomposition gives

Answer 29

a combination of sine waves with continuous frequencies

Question 30

bandwidth(Hz)=

Answer 30

maximum frequency - minimum frequency

Question 31

example of non-periodic composite signal

Answer 31

- AM and FM radio stations

Question 32

number of bits per level=

Answer 32

Log2(level)

Question 33

the more bits you can encode

Answer 33

the faster the data rate

Question 34

a digital signal is a composite analog | signal but..

Answer 34

it has an infinite bandwidth

Question 35

why is that what is sent, may not be what is received (what causes this effect)

Answer 35

- because of the bandwidth supported by the medium

Question 36

baseband (unfiltered) transmission of a digital signal, that preserves its shape, is possible only if..

Answer 36

we have a low pass channel with an infinite or very wide bandwidth

Question 37

what is a low pass channel

Answer 37

- a channel that allows frequencies that are near zero to be transferred - e.g BASEBAND

Question 38

bits and bandwidth in baseband transmission

Answer 38

- bandwidth is proportional to the bit rate | - to send bits faster, we need more bandwidth

Question 39

which type of signal does baseband transmit?

Answer 39

DIGITAL

Question 40

which type of signal does bandpass transmit?

Answer 40

ANALOG (CONVERT DIGITAL 2 ANALOG)

Question 41

two types of channels

Answer 41

- baseband | - bandpass

Question 42

transmission process in a bandpass channel

Answer 42

1. input digital signal 2. convert to analog 3. pass through the bandpass channel 4. convert to digital 5. digital signal output

Question 43

three causes for transmission impairment

Answer 43

1. distortion 2. attenuation 3. noise

Question 44

what is attenuation

Answer 44

amplitude has decreased

Question 45

how to *try* to fix attenuation

Answer 45

by amplification

Question 46

problem with amplification

Answer 46

will increase noise (MORE JUNK)

Question 47

what is distortion

Answer 47

sent signal differs from received signal

Question 48

what is noise

Answer 48

- unwanted signal(s)

Question 49

what is SNR

Answer 49

power of signal to power of noise ratio

Question 50

SNR(dB)=

Answer 50

power of signal/power of noise

Question 51

SNR (converting to dB)

Answer 51

10Log10(SNR)

Question 52

what device converts analog and digital signals to the other

Answer 52

MODEM | MODULATOR & DEMODULATOR