Analog Modulation

a

The "envelope" of an AM signal is due to

a. the baseband signal

b. the carrier signal

c. the amplitude signal

d. none of the above

b

Spectrum analysis is used to view which of the following characteristics of an RF signal?

a. phase

b. bandwidth

c. modulating wave

d. modulating envelope

c

Amplitude modulation that vary the carrier amplitude with the modulating signal by passing it through an attenuator work on the principle of

a. rectification

b. resonance

c. variable resistance

d. absorption

c

Overmodulation causes:

a. distortion

b. splatter

c. both A and B

d. none of the above

c

In an AM wave, where is the audio intelligence located?

a. in the carrier frequency

b. in the spacing between the sideband frequencies

c. in the spacing between the carrier and sideband frequencies

d. in the sideband frequencies

d

The component used to produce AM at very high frequencies is a:

a. varactor

b. thermistor

c. cavity resonator

d. PIN diode

a

A single-sideband signal contains 2 kW. How much power is contained in the carrier?

a. 0W

b. 500 W

c. 1 kW

d. 2 kW

c

At 100% modulation, the total sideband power is:

a. equal to the carrier power

b. twice the carrier power

c. half the carrier power

d. 1.414 x carrier power

d

In an FM signal, (a) the rate of shift is proportional to what characteristic of the modulating signal, and (b) the amount of shift is proportional to what characteristic?

a. (a) amplitude (b) amplitude

b. (a) amplitude (b) frequency

c. (a) frequency (b) frequency

d. (a) frequency (b) amplitude

d

If an AM radio station increases its modulation index, you would expect:

a. the audio to get louder at the receiver

b. the received RF signal to increase

c. the signal-to-noise ratio to increase

d. all of the above

c

Frequencies that are located between adjacent channels to prevent interference are referred to as:

a. sidebands

b. bandwidths

c. guard bands

d. blank channels

c

The modulation index can be derived from

a. the time-domain signal

b. the frequency-domain signal

c. both a and b

d. none of the above

c

What type of circuit is used to remove the AM component in the output of a semiconductor reactance modulator?

a. a mixer

b. a filter

c. a limiter

d. a buffer amplifier

c

The most commonly used amplitude demodulator is the

a. diode mixer

b. balanced modulator

c. envelope detector

d. crystal filter

b

In AM, at 100% modulation:

a. overmodulation will occur

b. the peak voltages of the modulating signal and the carrier are equal

c. it is the typical value of the modulation index

d. all of these

c

The main problem in using quadrature AM would be:

a. requires too much bandwidth

b. requires too much power

c. incompatibility with ordinary AM radios

d. all of the above

d

Which symbol in radio signal emission designation is referred to type of modulation of the main carrier?

a. second

b. fourth

c. third

d. first

d

As compares to plain AM, SSB AM:

a. is more efficient

b. requires a more complex demodulator circuit

c. requires less bandwidth

d. all of the above

a

As the positive potential is increased on the cathode of a varactor, (a) what happens to reverse bias and (b) how is dielectric width affected?

a. (a) increases (b) increases

b. (a) increases (b) decreases

c. (a) decreases (b) decreases

d. (a) decreases (b) increases

c

A widely used balanced modulator is called the

a. diode bridge circuit

b. full wave bridge rectifier

c. lattice modulator

d. balanced bridge modulator

c

Which of the following is not true about AM?

a. the carrier amplitude varies

b. the carrier frequency remains constant

c. the carrier frequency changes

d. the information signal amplitude changes the carrier amplitude

d

If an SSB transmitter radiates 1000 watts at peak modulation, what will it radiate with no modulation?

a. 1000 Watts

b. 500 Watts

c. 250 Watts

d. 0 Watts

b

In a phase modulator, the frequency during the constant-amplitude portion of the modulating wave is the

a. peak frequency

b. rest frequency

c. deviation frequency

d. modulating frequency

b

In a diode ring modulator, the diode acts like

a. variable resistor

b. switches

c. rectifiers

d. variable capacitors

b

First symbol in the designation of radio signals emission which refers to use of an unmodulated carrier.

a. J

b. N

c. H

d. A

c

Music on AM radio stations is "low-fidelity" because:

a. AM is susceptible to noise

b. commercial AM stations use low power

c. commercial AM stations have a narrow bandwidth

d. all of the above

d

In phase modulation, (a) the amplitude of the modulating signal determines what characteristic of the phase shift, and (b) the frequency of the modulating signals determines what characteristic of the phase shift?

a. (a) rate (b) rate

b. (a) rate (b) amount

c. (a) amount (b) amount

d. (a) amount (b) rate

b

In AM, what is the modulation index?

a. the term used to describe the amount of frequency change in an am waveform

b. also known as depth of modulation

c. it is computed as the ratio of carrier voltage and modulating voltage

d. all of these

d

The type of information that can be sent using AM is

a. audio

b. video

c. digital data

d. all of the above

c

The primary advantage of phase modulation over frequency modulation is that phase modulation has better carrier

a. power stability

b. amplitude stability

c. frequency stability

d. directional stability

c

The most commonly used filter in SSB generators uses:

a. LC networks

b. mechanical resonators

c. crystal

d. RC networks and op amps

b

A third symbol emission which represent data transmission including telemetry and telecommand

a. B

b. D

c. C

d. N

c

To demodulate a USB SSB signal, the receiver must

a. be set to USB mode

b. reinsert the carrier

c. both a and b

d. none of the above

d

When a carrier is modulated by a square wave, what maximum number of sideband pairs will be generated?

a. 1

b. 9

c. 3

d. infinite

d

The equivalent circuit id a quartz crystal is a:

a. series resonant circuit

b. paralle resonant circuit

c. neither a nor b

d. both a and b

b

Indicate which one of the following is not an advantage of FM over AM

a. better noise immunity is provided

b. lower bandwidth is required

c. the transmitted power is more useful

d. less modulating power is required

b

The FM modulation index

a. increases with both deviation and modulation frequency

b. increases with deviation and decreases with modulation frequency

c. decreases with deviation and increases with modulation frequency

d. is equal to twice the deviation

b

When FM reception deteriorates abruptly due to noise, it is called

a. the capture effect

b. the threshold effect

c. reduced distortion

d. the limit effect

d

When compared to a conventional AM signal, an SSB signal provides which of the following advantages

a. improved frequency stability

b. increased receiver gain

c. reduced distortion

d. reduced bandwidth

b

If the amplitude of the modulating signal decreases, the carrier deviation

a. increases

b. decreases

c. remains constant

d. goes to zero

d

Widest bandwidth in a double-tuned circuit is obtained with

a. undercoupling

b. critical coupling

c. optimum coupling

d. overcoupling

b

Automatic gain control permits a wide range of signal amplitudes to be accommodated by controlling the gain of the

a. RF amplifier

b. IF amplifier

c. mixer

d. AF amplifier

d

An AFC is used to correct for

a. audio distortion

b. strong input signals

c. instability in the IF amplifier

d. frequency drift in the LO

b

The function of AFC is

a. maintain a constant IF frequency

b. match the local oscillator to the received signal

c. lock the discriminator to the IF frequency

d. none of the above

c

To maintain function of the AGC is to

a. keep the gain of the receiver constant

b. keep the gain of the IF amplifiers constant

c. keep the input to the detector at a constant amplitude

d. all of the above

c

A BFO is used in the demodulation of which types of signals?

a. AM

b. FM

c. SSB or CW

d. phase inversion

a

An FM receiver switching suddenly between two stations on nearby frequencies is called

a. the capture effect

b. the threshold effect

c. the "two-station" effect

d. none of the above

a

In the phasing method of SSB generation, one sideband is canceled out due to

a. phase shift

b. sharp selectivity

c. carrier suppression

d. phase inversion

c

Audio signals are not propagated directly to space because

a. to do so will entail additional costs

b. the signal will be highly attenuated

c. they will require antennas that are too long

d. the signal that will be propagated will be too weak

c

A resonant circuit is

a. a simple form of bandpass filter

b. used in narrowband RF amplifiers

c. both a and b

c. none of the above

d

What is the purpose of buffer amplifier?

a. to provide a direct connection between the oscillator and the load

b. to amplify the output signal of the oscillator

c. to remove frequency distortion from the oscillator

d. to prevent load variations from affecting the oscillator

b

A balanced modulator used to demodulate a SSB signal is called a(n)

a. transponder

b. product detector

c. converter

d. modulator

b

Loading down a tuned-circuit amplifier will

a. raise the Q of the tuned circuit

b. lower the Q of the tuned circuit

c. "multiply" the Q

d. have no effect on Q

d

In a buffer amplifier, what is the impedance in the (a) input and (b) output?

a. (a) low (b) low

b. (a) low (b) high

c. (a) high (b) high

d. (a) high (b) low

d

Frequency translation is done with a circuit called a

a. summer

b. multiplier

c. filter

d. mixer

b

In RF amplifiers, impedance matching is usually done with

a. RC coupling

b. transformer coupling

c. direct coupling

d. lumped reactance

a

The ability of a circuit to faithfully reproduce the input signal in the output is known by what term?

a. fidelity

b. fluctuation

c. directivity

d. discrimination

c

The inputs to mixer are fo and fm. In down conversion, which of the following mixer output signal is selected?

a. fo

b. fm

c. fo-fm

d. fo+fm

c

To provide two or more voice circuits with the same carrier, what system must be used?

a. vestigial sideband system

b. pilot carrier system

c. ISM emission

d. limcomplex

d

One of the following cannot be used to remove unwanted sideband in SSB. This is the

a. filter system

b. third method

c. phase shift method

d. balanced modulator

c

In an AM transmitter with 100% modulation, the voltage of the final RF stage will be

a. approximately half the DC supply voltage

b. approximately twice the DC supply voltage

c. approximately four times the DC supply voltage

d. none of the above

b

Over a narrow range of frequencies, the PLL acts like a

a. low-pass filter

b. bandpass filter

c. tunable oscillator

d. frequency modulator

b

With a sine-wave input, how will the output compare to the input in (a) a linear circuit (b) a nonlinear circuit?

a. (a) proportional (b) proportional

b. (a) proportional (b) not proportional

c. (a) not proportional (b) not proportional

d. (a) not proportional (b) proportional

a

For a "frequency multiplier" to work, it requires

a. a nonlinear circuit

b. a linear amplifier

c. a signal containing harmonics

d. an input signal that is an integer multiple of the desired frequency

a

Overall sensitivity of a receiver is limited by which of the following factors?

a. noise

b. bandwidth

c. output power

d. frequency response

d

On an FM signal, maximum deviation occurs at what point on the modulating signal?

a. zero-crossing point

b. peak positive amplitude

c. peak negative amplitude

d. both b and c

a

Pre-emphasis is used to

a. increase the signal to noise ratio for higher audio frequencies

b. increase the signal o noise ratio for lower audio frequencies

c.increase the signal to noise ratio for all audio frequencies

d. allow stereo audio to be carried by FM stations

a

Practical transmitters are usually designed to drive a load impedance of

a. 50 ohms resistive

b. 75 ohms resistive

c. 300 ohms resistive

d. 600 ohms resistive

b

A modulator circuit performs what mathematical operation on its two inputs?

a. addition

b. multiplication

c. division

d. square roots

b

Why are image frequencies somewhat less of a problem in FM receivers than they are in SSB or AM receivers?

a. SSB uses less bandwidth than does FM

b. FM signals have a capture effect characteristics

c. FM mixer stages are square-law devices

d. FM receivers do not use the superheterodyne design

d

A class D amplifier is

a. very efficient

b. essentially pulse-width modulation

c. essentially pulse-duration modulation

d. all of the above

d

What is the disadvantage of TRF?

a. the bandwidth is inconsistent and varies with center frequency when tuned over a wide range of frequencies

b. instability due to the large number of amplifier all tunes to the center frequency

c. gains are not uniform over a wide range of frequency range

d. all of the above

b

To generate a SSB signal

a. start with full-carrier AM

b. start with DSBSC

c. start with a quadrature signal

d. all of the above

d

If m is greater than 1, what happens?

a. normal operation

b. carrier drops to zero

c. carrier frequency shifts

d. information signal is distorted

c

What is the purpose of a buffer amplifier stage in a transmitter?

a. it prevents transmitters from producing spurious frequencies in the output signals

b. it provides power amplification with high efficiency

c. its high input impedance prevents oscillators from drifting off frequency

d. it amplifies audio frequencies before modulation occurs

a

The carrier is suppressed in

a. a balanced modulator

b. a mixer

c. a frequency multiplier

d. none of the above

b

For ideal AM, which of the following is true?

a. m=0

b. m=1

c. m<1

d. m>1

c

Image frequency problems would be reduced by

a. having an IF amplifier with the proper shape factor

b. having a wideband RF amplifier after the mixer

c. having a narrowband RF amplifier before the mixer

d. none of the above

c

To remove one AM sideband and leave the other you could use

a. a mechanical filter

b. a crystal filter

c. both a and b

d. none of the above

b

In superhet, which is considered as the first detector?

a. RF amplifier

b. mixer

c. IF section

d. detector

a

A direct FM modulator

a. varies the frequency of the carrier oscillator

b. integrates the modulating signal

c. both a and b

d. none of the above

a

Overmodulation occurs when

a. Vm > Vc

b. Vm < Vc

c. Vm= Vc

d. Vm= Vc = 0

b

In direct FM modulator

a. requires a varactor in the carrier oscillator

b. varies the phase of the carrier oscillator

c. both a and b

c. none of the above

d

The new signals produced by modulation are called

a. spurious emissions

b. harmonics

c. intermodulation products

d. sidebands

b

Frequency mutipliers are

a. essentially balanced modulators

b. essentially class C amplifiers

c. essentially mixers

d. none of the above

a

Most of the power in an AM signal is in the

a. carrier

b. upper sideband

c. lower sideband

d. modulating signal

c

With mixing

a. the carrier frequency can be raised

b. the carrier frequency can be lowered

c. the carrier frequency can be changed to any required value

d. the deviation is altered

c

In an AM signal, the transmitted information is contained within the

a. carrier

b. modulating signal

c. sidebands

d. envelope

a

The two basic specifications for a receiver are

a. the sensitivity and selectivity

b. the number of converters and the number of IFs

c. the spurious response and the tracking

d. the signal and the noise

c

What is the minimum AM signal needed to transmit information?

a. carrier plus sidebands

b. carrier only

c. one sideband

d. both sidebands

d

The "front end" of a receiver can include

a. the tuner

b. the RF amplifier

c. the mixer

d. all of the above

a

The main advantage of SSB over standard AM or DSB is

a. less spectrum space is used

b. simpler equipment is used

c. less power is consumed

d. a higher modulation percentage

c

In SSB which sideband is the best to use?

a. upper

b. lower

c. neither

d. depends upon the use

c

The frequency of the local oscillator

a. is above the RF frequency

b. is below the RF frequency

c. can be either above or below the RF frequency

d. is fixed, typically at 455 kHz

d

The local oscillator and mixer are combined in one device because

a. it gives a greater reduction of spurious responses

b. it increases sensitivity

c. it increases selectivity

d. it is cheaper

a

Basically, sensitivity measures

a. the weakest signal that can be usefully received

b. the highest-frequency signal that can be usefully received

c. the dynamic range of the audio amplifier

d. none of the above

c

The maximum power of typical transistor RF power amplifiers is in what range?

a. kilowatts

b. milliwatts

c. hundreds of watts

d. watts

b

Basically, selectivity measures

a. the range of frequencies that the receiver can select

b. with two signals close in frequency, the ability to receive one and reject the other

c. how well adjacent frequencies are separated by the demodulator

d. how well the adjacent frequencies are separated in the mixer

a

Maximum power transfer occurs when what relationship exists between the generator impedance Zi and the load impedance ZL:

a. Zi = ZL

b. Zi > ZL

c. Zi < ZL

d. Zi = 0 ohm

c

When comparing values for shape factor

a. a value of 1.414 dB is ideal

b. a value f 0.707 is ideal

c. a value of 1.0 is ideal

d. there is no ideal value