Unit 1 Modulation and Multiplexer

Question 1

The process of modifying any characteristic of an information signal or carrier signal so that it varies in step with the instantaneous value of another information signal.

Answer 1

Modulation. (1-2)

Question 2

What are the 2 basic types of modulation techniques used in communications?

Answer 2

Analog and Digital Modulation. (1-2)

Question 3

What is the conversion of an analog signal (the information) into another analog signal (the carrier)?

Answer 3

Analog Modulation. (1-2)

Question 4

Analog modulation can be divided into what three techniques?

Answer 4

AM - varies amplitude, or strength, of carrier signal
FM - varies frequency, or pitch, of carrier signal
PM - varies phase , or time displacement of signal (1-2)

Question 5

What are the basic types of digital conversion techniques?

Answer 5

ASK - Amplitude shift keying
FSK - Frequency shift keying
PSK - Phase shift keying (1-2)

Question 6

What converts a digital signal to analog form by varying the amplitude of the carrier signal. Also known as on-off keying (OOK) because amplitude of carrier was either on or off depending on state of digital input.

Answer 6

ASK - Amplitude shift keying (1-2)

Question 7

What converts a digital signal to analog form by varying the frequency of the carrier signal. It changes the center frequency from one value to another depending on state of the digital input.

Answer 7

FSK - Frequency shift keying (1-2)

Question 8

What converts a digital signal to analog form by varying the phase, or time displacement, of the carrier signal. It changes the phase of frequency from one value to another depending on state of the digital input.

Answer 8

PSK - Phase shift keying (1-3)

Question 9

What are three forms of PSK?

Answer 9

BPSK - Binary phase shift keying
QPSK - Quadrature phase shift keying
DPSK - Differential phase shift keying (1-3)

Question 10

Simplest form of PM. Converts digital signal to analog form by varying phase of carrier signal. Two phase shifts (0 or 180 degrees) for data transmission depending on whether a binary 1 or 0 is to be transmitted.

Answer 10

BPSK - Binary phase shift keying (1-3)

Question 11

Uses 4 different carrier phases (0, 90, 180, and 270 degrees) to represent 2 transmission bits.

Answer 11

QPSK - Quadrature phase shift keying (1-3)

Question 12

Encodes different digital values as changes in signal phase, Easier to implement and is more robust that PSK because it looks for differences, rather than specific values. Can be found in LAN technologies.

Answer 12

DPSK - Differential phase shift keying (1-3)

Question 13

What can use all 3 variable parameters of frequency, amplitude, or phase at the same time to convert digital signal information. An example is Quadrature Amplitude Modulation (QAM).

Answer 13

Combined modulation systems (1-3)

Question 14

Combination of Amplitude Modulation and Phase Modulation. Converts a digital signal to analog form by varying the amplitude and phase of the carrier signal. Able to encode 4 data bits for transmission. Similar to QPSK.

Answer 14

Quadrature Amplitude Modulation (QAM) (1-3)

Question 15

Conversion of analog signal (the information) into a digital signal (the carrier). The technique can be pulse or delta modulation.

Answer 15

Digital Modulation (1-3)

Question 16

Varies one or more parameters of a pules according to a modulating signal to transmit the desired information.

Answer 16

Pulse modulation (1-3)

Question 17

Simplest kind of pulse-modulation technique and is amplitude-modulated. Used for time-division multiplexing and differs from AM mainly in the use of a rectangular pulse train rather than a sine wave for the carrier signal.

Answer 17

Pulse-amplitude modulation (1-3)

Question 18

Also known as pulse-width modulation (PWM), pulse-length modulation (PLM), or pulse-time modulation (PTM). Duration, or width, of each sample pulse is varied to encode an analog signal at the point of sampling. Less affected by noise than the PAM method.

Answer 18

PDM - Pulse-duration modulation (1-3,1-4)

Question 19

Used in military TDM. Uses a pulse time method that represents an analog signal by varying the position (the time displacement) of a discrete pulse within a bit interval,

Answer 19

PPM - Pulse-position modulation (1-4)

Question 20

Complete digitization process since it converts an analog signal into one that is discrete with respect to both time and amplitude (or polarity). Based on analog signal already modulated (by PAM, PDM, or PPM). Uses quantizer.

Answer 20

PCM - Pulse code modulation (1-4)

Question 21

Variation of PCM. Amplitude represented using 4-bit values (rather than 8 used in PCM), and 32Kbs data transfer rate instead of 64Kps, as in PCM.

Answer 21

ADPCM - Adaptive differential pulse-code modulation (1-4)

Question 22

Converts an analog signal by scanning it a specified amount of times. If value of sample is different from previous scan, the digital signal is modified by a discrete step.

Answer 22

DM - Delta Modulation (1-4)

Question 23

Variation of DM where a signal’s step may vary in size from sample to sample. A simple form is CVSD.

Answer 23

ADM - Adaptive delta modulation (1-4)

Question 24

Varies the signal step size according to the input signal amplitude. Lower input = smaller steps. Higher input = larger steps.

Answer 24

CVSD - Continuous variable slope delta modulation (1-4)

Question 25

What are 4 basic types of pulse modulation?

Answer 25

PAM, PDM, PPM, and PCM. (1-5)

Question 26

What frequencies are present at the output of an AM modulator?

Answer 26

Frequency Carrier, carrier minus the modulated signal frequency, carrier plus the modulated frequency.