Unit 3-1

Front 1

1.(401) Modulation enables signals to be transmitted at frequencies

Back 1

Higher than original

Front 2

2.(401) What purpose of modulation involves modulationg low frequency signals for transmission over long distances?

Back 2

Ease of Radiation

Front 3

3.(402) What factor determines the spacing of the sidebands in an amplitude modulated signal?

Back 3

Frequency of the modulating signal

Front 4

4.(402) The relationship of the bandwidth required for DSBEC AM to the bandwidth of the modulating signal of the AM bandwidth alone is

Back 4

twice the modulating bandwidth

Front 5

5.(403) What type of device is used to recover the intelligence signal in DSBSC modulation?

Back 5

Heterodyne detector.

Front 6

6.(403) In double sideband suppressed carrier modulation, the intelligence is reconstrcuted by modulating the received signal at the exact frequency and phase relation as the

Back 6

carrier frequency

Front 7

7.(404) What is the relationship of the SSBSCs bandwidth compared to DSBEC or DSBSC signals?

Back 7

SSBSC requires half the bandwidth of the other two.

Front 8

8.(405) The ouptut of the oscillator in a FM modulator increases in frequency with each

Back 8

positive half cycle of the modulating signal

Front 9

9.(405) In FM, the amount of oscillator frequency change is

Back 9

directly proportional to the amplitude of the modulating signal

Front 10

10.(405) A 10kHz modulating signal has enough peak voltage to cause a deviation of 30 kHz. What is the modulation index?

Back 10

3

Front 11

11.(405) How many sidebands does FM produce?

Back 11

an unlimited number

Front 12

12.(406) In PM, the carrier's

Back 12

phase is shifted at the rate of the modulating signal

Front 13

13.(406) By using 8-PSK instead of binary phase shift keying, information capacity in increased

Back 13

three times

Front 14

14.(407) What is the first step in the pulse code modulation process?

Back 14

The analog signal is band-limited

Front 15

15.(407) Non-uniform quantizing and companding decreases the lengh of the code word from

Back 15

11 to 7 bits

Front 16

16.(408) How fast can an asychronous transfer mode network potentialy move data?

Back 16

600 Mbps

Front 17

17.(408) How does sychrounous transmission reduce the overhead costs of data transmission?

Back 17

blocks many characters together for transmission

Front 18

18.(409) Which RS-232C signal is the data from the data communications equipment to the data terminal equipment?

Back 18

recieve data

Front 19

19.(409) Which RS-232C siganl indicates the modem is ready to transfer data?

Back 19

Data set ready

Front 20

20.(409) The minimum pins required to establish a two-way data communications path with the RS-232 standard are

Back 20

Pins 2,3 7

Front 21

21.(410) Which standard designates the electrical standards for a balanced voltage digital interface circuit?

Back 21

RS-422

Front 22

22.(410) What is the transition region voltage in an RS-422 line driver?

Back 22

-2.0 to +2.0

Front 23

23.(410) Which standard uses many of the same pins and funcions as RS-232?

Back 23

RS-530

Front 24

24.(411) Approximately what percentage of all nework problems are cable related according to the National Assocition of Communications Contractors?

Back 24

70 percent

Front 25

25.(412) When using vertical redundancy check, what signaificance does the amount of ones have in a data bit pattern?

Back 25

Determines parity

Front 26

26.(412) Using the longitudianl redundancy check method of error correction, what does the reciever compare with the transmitter to ensure an accurate transmission of data?

Back 26

The checksum

Front 27

27.(412) What two error detection methods, when used together,are 98 percent effective in detecting errors?

Back 27

Vertical redundancy check and longitudianl redundancy check

Front 28

28.(413) What is the most common error correction technique?

Back 28

Automatic retransmit on request

Front 29

29.(413) When using forward error control as a method error correction, where does eror correction take place?

Back 29

Recieving end

Front 30

1.[401] What are the 2 primary purposes to modulate a signal?

Back 30

Ease of radiation and channel allocation

Front 31

2.[401] What first must be done to radiate a signal over long distances?

Back 31

The signal must first be converted to analog format

Front 32

1.[402] Name the part of the AM carrier that varies according to the modulating signal.

Back 32

The amplitude

Front 33

2.[402] What frequencies are present at the output of an AM modulator?

Back 33

Carrier frequency, carrier plus the modulating frequency, and carrier minus the modulating frequency

Front 34

3.[402] What would be the frequencies at the output of the modulator when you modulate a 500 kHz carrier with a 2 kHz tone?

Back 34

500kHz 498kHz and 502kHz

Front 35

4.[402] In conventional AM(DSBEC), what is the relation between the bandwidth required to transmit the signal and the bandwidth of the modulating signal?

Back 35

the bandwidth required is twice the modulating signal

Front 36

5.[402] What part of the bandwidth of a DSBEC signal carries the information signals?

Back 36

the sidebands

Front 37

6.[402] State the main disadvantage of DSBEC AM.

Back 37

it wastes power

Front 38

1.[403] Briefly describe the DSBSC process.

Back 38

An AM process that transmits both sidebands minus the carrier

Front 39

2.[403] In DSBSC operation, what parts of the transmitted signal carries information?

Back 39

Both the amplitude and phase of the output signal carry information.

Front 40

3.[403] In DSBSC, what must we do to recover the original intelligence signal?

Back 40

Reinsert the carrier

Front 41

1.[404] Briefly describe the SSBSC process.

Back 41

An AM process that transmits one sideband without a carrier

Front 42

2.[404] Why is SSBSC far more efficient than DSBEC and DSBSC?

Back 42

It makes better use of power and bandwidth.

Front 43

1.[405] What determines the amount of deviation of a FM carrier?

Back 43

the amplitude of the modulating signal

Front 44

2.[405] How does the rate of deviatoin relate to the frequency of the modulating signal?

Back 44

They are directly porportional

Front 45

3.[405] Who determines the maximum amount of deviation in FM?

Back 45

The FCC establishes the maximum amount of deviation.

Front 46

4.[405] How do you determine the modulation index in FM?

Back 46

by dividing the amount of frequency deviation by the frequency of the modulating signal

Front 47

5.[405] What is a significant sideband?

Back 47

a sideband that contains at least 1 percent of the total trnasmitted power.

Front 48

6.[405] Where do FM sidebands get their power?

Back 48

from the unmodulated carrier

Front 49

7.[405] What is the relationship between modulation index and sideband power?

Back 49

A higher modulation index means more power in the sidebands. It is even possible to have all the power in the sidebands and none in the carrier. At this point,any further increase in modulation would start taking power from the sidebands and placing it back in the carrier resulting in a redistribution of power.

Front 50

1.[406] What effect does the change in carrier frequency have in PM?

Back 50

None. The frequecy change in PM is incidental

Front 51

2.[406] Describe the effect the positive and negative alteration of a modulating signal has on the phase of the carrier in PM.

Back 51

During the positive alternation of the modulating signal, the phase of the carrier lags behind the unmodulated carrier. During the negative alternation it leads the unmodulated carrier.

Front 52

3.[406] When is the carrier at its rest frequency in PM?

Back 52

During the constant amplitude part of the modulating frequency.

Front 53

4.[406] What part of the modulating signal controls the amount of phase shift in PM?

Back 53

amplitude

Front 54

5.[406] What part of the modulating signal controls the rate of phase shift?

Back 54

frequency

Front 55

6.[406] How can you increase effieciency in digital modulation?

Back 55

by using multilevel encoding

Front 56

7.[406] Describe the QPSK process.

Back 56

The input NRZ signal is split into 2 directions (I-rail and Q-rail), each at 1/2 the data rate. The Q-rail signal is phase shifted 90 degrees and both are modulated in biphase modulators. The signals are recombined to form the QPSK signal

Front 57

8.[406] What are the 2 reasons for using higher levels of PSK?

Back 57

To increase capacity or decrease modulation rate

Front 58

9.[406] How many bits are grouped in 8 psk? 16 psk?

Back 58

3 bit combination; 4 bit combination

Front 59

10.[406] What is the main disadvantage of higher level PSK?

Back 59

You need a higher S/N ratio.

Front 60

1.[407] Define the term
"digitization"

Back 60

The process of converting analog signals into digital signals

Front 61

2.[407] Name the four steps of PCM

Back 61

Band limiting,sampling,quantizing, and encoding

Front 62

3.[407] State the main purpose of the band-limiting filter.

Back 62

It ensures the input to the sampler never exceeds a maximum frequency.

Front 63

4.[407] Define sampling

Back 63

converting a continuous time signal into a discrete time signal

Front 64

5.[407] What part of the pulse train is varied using PAM,PWM, and PPM?

Back 64

PAM=amplitude; PWM= width or duration; PPM= position

Front 65

6.[407] What is sthe Nyquist samping rate?

Back 65

Sampling the input at twice its highest frequency

Front 66

7.[407] Which step of PCM assigns discrete amplitude values to the sampled amplitude values?

Back 66

Quantization

Front 67

8.[407] Name the two methods of quantization.

Back 67

Uniform quantizing, non-uniform quantizing

Front 68

9.[407] Which method assigns amplitude values bases on an equal amplitude range?

Back 68

Uniform quantizing

Front 69

1.[408] At what speed does ATM operate?

Back 69

600 Mbps or higher

Front 70

2.[408] Which ATM, what is the length of each transmission unit?

Back 70

One character in length

Front 71

3.[408] What part of an ATM transmission tells the receiving device that a character is coming and that the character has been sent?

Back 71

The start and stop bits

Front 72

4.[408] How does the receiving device determine whether it has received a correct character?

Back 72

By summing the 1 bits

Front 73

5.[408] What is an advantage of synchronous transmission over asynchronous transmission?

Back 73

To reduce the overhead costs of data transmission

Front 74

6.[408] How does synchronous transmission differ from asychrounous transmisison?

Back 74

Sychronous transmission blocks many characters together for transmission

Front 75

1.[409] What capability does the RS-232C standard provide?

Back 75

A standard for compatibility between communications devices

Front 76

2.[409] What is data communicatins equipment?

Back 76

the modem

Front 77

3.[409] What is data terminal equipment?

Back 77

The terminal or computer

Front 78

4.[409] What is the maximum lenth of the RS-232C cable at 56 Kbps?

Back 78

50 feet

Front 79

5.[409] What voltages represent the logic levels for data in the RS-232C standard?

Back 79

Logic 0 equals a voltage between +5 and +15. Logic 1 equals a voltage between
-5 and -15 volts.

Front 80

6.[409] What indicates the start of serial data transmission?

Back 80

The start bit

Front 81

7.[409] How many stop bits are allowed by the RS-232C standard?

Back 81

1,1.5,or 2 stop bits

Front 82

8.[409]Which RS-232C pins carry data?

Back 82

Pin 2(transmits data) and pin 3 (receives data)

Front 83

9.[409] What is the purpose of the Clear to Send signal on pin 5?

Back 83

To indicate the modem is ready to recieve data from the computer.

Front 84

10.[409] What does the Data Terminal Ready signal on pin 20 indicate?

Back 84

The data terminal is powered up and operational.

Front 85

11.[409] Which lines are used for handshaking between the computer and peripheral equipment?

Back 85

DTE, DCE, Data Terminal Ready, and Data Set Ready.

Front 86

1.[410] What are the two ways to connect equipment to transmit serial data signals?

Back 86

By single-ended and differential transmission.

Front 87

2.[410] What are the distance and data rates for the RS-422 standard?

Back 87

For data rates up to 10Mbps, up to 40 feet; for data rates between 100 Kbps and 10 Mbps, up to 4,000 feet

Front 88

3.[410] What components make up the RS-422 digital interface?

Back 88

Line drivers(also called generators) and line recievers interconnected by a balanced cable.

Front 89

5.[410] What peak-to-peak voltage does the RS-422 driver produce?

Back 89

4.0 to 12.0 volts peak-to-peak

Front 90

6.[410] What are the distance and data rates for the RS-423?

Back 90

100 Kbps for up to 300 feet; if the data rate is less than 1 Kbps, up to 4,000 feet

Front 91

7.[410]What is the peak-to-peak voltage and the impedance for the Rs-423 line driver?

Back 91

4.0 to 12.0 volts peak-to-peak (maximum operating range); impedance is 100 ohms or less

Front 92

8.[410] What is the RS-530 physical specification?

Back 92

A 25 pin D-type connector

Front 93

9.[410] Why was the RS-530 standard developed?

Back 93

In response to the disadvantages of the RS-449 standard.

Front 94

10[410]. With which electrical interfaces was the RS-530 standard designed to be used?

Back 94

With the electrical interfaces of RS-422 adn RS-423 for synchronous or asynchronous transmission.

Front 95

11.[410] What are the data rates for the RS-530 standard with balanced circuits?

Back 95

20Kbps to 2Mbps, with balanced circuits

Front 96

12[410]. For what applications is V.35 most used currently?

Back 96

Internodal trunks between x.25 exchanges.

Front 97

1.[411] According to the National Association of Communications Contractors, what percentage of network problems can be traced to cabling problems?

Back 97

70 percent

Front 98

2.[411] In what year did the EIA develop the first building telecommucications cabling systems standards?

Back 98

1985

Front 99

3.[411]What is the useful life of a building distribution system using TIA/EIA 568 standards?

Back 99

10 years

Front 100

4.[411] How often are TIA/EIA standards reviewed for currency?

Back 100

five years

Front 101

5.[411]How many levels are contained in the TIA/EIA category system?

Back 101

5

Front 102

1.[412] What does VRC check each incoming character for?

Back 102

odd or even parity

Front 103

2.[412] What is even partity?

Back 103

There is and even number of ones in the bit pattern for each character

Front 104

3.[412]What is the difference between VRC and LRC?

Back 104

VRC checks each character for odd parity; LRC checks and entire horizontal line within a block for odd or even parity

Front 105

4.[412] What transmitted character does the receiver use to determine if a transmission was error-free?

Back 105

BCC

Front 106

5.[412]When using the checksum method of error detection, what binary number is used to divide the sum of all the characters in order to derive the checksum?

Back 106

255

Front 107

6.[412] How does the CRC method of error detection determine the dividend when computing the BCC?

Back 107

CRC treats the binary ones and zeros in the frame address,control, and information fields as one long binary number

Front 108

7.[412]How effective is CRC at detecting errors in most applications?

Back 108

99 percent

Front 109

1.[413] How does ARQ work?

Back 109

The reciever automatically sends a retransmittal request to the sender if an error is found in a recieved frame.

Front 110

2.[413] What is the most common method of error correction?

Back 110

ARQ

Front 111

3.[413] On what type of circuits is forward error control most useful?

Back 111

On circuits with extremely high error rates or on 1-way broadcast circuits

Front 112

4.[413]Using forward error control, at which end of the transmission link are errors corrected?

Back 112

recieving end

Front 113

5.[413] Using forward error control, what is the transmitter's function in error correction?

Back 113

to transmit multiple copies of the same message to the distant end.

Front 114

6.[413]Using forward error control, what is the receiver's function in error correction?

Back 114

To compare all copies of transmitted message, then reconstruct the message using the good portions of the message copies received.