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Flashcards in Mod 12 CH 2,3 Deck (69)
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1

What are the two types of angle modulation?

Frequency and phase

2

Name the modulation system in which the frequency alternates between two discrete values in response to the opening and closing of a key?

Frequency-shift keying.

3

What is the primary advantage of an fsk transmission system?

Resistance to noise interference.

4

What characteristic of a carrier wave is varied in frequency modulation?

Instantaneous frequency.

5

How is the degree of modulation expressed in an fm system?

As the ratio of the frequency deviation to the maximum frequency deviation allowable.

6

What two values may be used to determine the bandwidth of an fm wave?

The number of significant sidebands and the modulating frequency.

7

How does the reactance-tube modulator impress intelligence onto an rf carrier?

By changing the reactance of an oscillator circuit in consonance with the modulating voltage

8

What characteristic of a transistor is varied in a semiconductor-reactance modulator?

Collector-to-emitter capacitance.

9

What circuit section is required in the output of a multivibrator modulator to eliminate unwanted output frequencies?

An LCR filter.

10

What characteristic of a varactor is used in an fm modulator?

Capacitance.

11

What type of modulation depends on the carrier-wave phase shift?

Phase.

12

What components may be used to build a basic phase modulator?

A phase-shift network such as a variable resistor and capacitor in series.

13

Phase-shift keying is similar to what other two types of modulation?

Cw and frequency-shift keying.

14

Overmodulating an rf carrier in amplitude modulation produces a waveform which is similar to what modulated waveform?

Pulse modulation.

15

What is prt?

Pulse-repetition time.

16

What is nonpulse time?

Rest time.

17

What is average power in a pulsed system?

Peak power during a pulse averaged over pulse time plus rest time.

18

What is the primary component for a spark-gap modulator?

Either a fixed spark gap that uses a trigger pulse to ionize the air between the contacts, or a rotary gap that is similar to a mechanical switch.

19

What are the basic components of a thyratron modulator?

Power source, a circuit for storing energy, a circuit for discharging the storage circuit, and a pulse transformer.

20

What action is necessary to impress intelligence on the pulse train in pulse modulation?

Some characteristic of the pulses has to be varied.

21

To ensure the accuracy of a transmission, what is the minimum number of times a modulating wave should be sampled in pulse modulation?

2.5 times the highest modulating frequency.

22

What, if any, noise susceptibility advantage exists for pulse-amplitude modulation over analogamplitude modulation?

Both are susceptible to noise and interference.

23

What characteristics of a pulse can be changed in pulse-time modulation?

The time duration of the pulses or the time of occurrence of the pulses.

24

Which edges of the pulse can be modulated in pulse-duration modulation?

Either, or both at the same time.

25

What is the main disadvantage of pulse-position modulation?

It requires synchronization between the transmitter and receiver.

26

What is pulse-frequency modulation?

A method of pulse modulation in which a modulating wave is used to frequency modulate a pulse-generating circuit

27

Pulse-code modulation requires the use of approximations of value that are obtained by what process?

Quantization.

28

If a modulating wave is sampled 10 times per cycle with a 5-element binary code, how many bits of information are required to transmit the signal?

50.

29

What is the primary advantage of pulse-modulation systems?

Low susceptibility to noise.

30

What is demodulation?

Re-creating original modulating frequencies (intelligence) from radio frequencies.