ch3 - modulation

Upload: norman-oco

Post on 08-Oct-2015

207 views

Category:

Documents


11 download

DESCRIPTION

Modulation: 3001 Comms

TRANSCRIPT

- AM/FM- ____________ determines the number of sideband components in FM. a. Carrier frequency b. Modulation frequency c. Modulation index d. Deviation ratio ans: c- One of the following transmits only sideband. a. H3E b. R3E c. A3E d. B8E ans: a- What produces the sidebands on FM? a. Signal amplitude b. Carrier harmonics c. Baseband frequency d. Broadband frequency ans: c- Which test instrument displays the carrier and the sidebands amplitude with frequency to frequency? a. Oscilloscope b. Spectrum analyzer c. Frequency analyzer d. Amplitude analyzer ans: b- Mixer is also known as __________. a. modulator b. suppressor c. converter d. beater ans: c- Which one of the following emission transmit the lower sideband and half of the upper sideband. a. A5C b. J3E c. A3J d. A3H ans: d- An FM receive signal ___________. a. vary in amplitude with modulation b. vary in frequency with modulation c. vary in frequency and amplitude with wideband modulation d. is not immune to noise ans: b- The process of impressing intelligence on the carrier is called a. modulation b. detection c. mixing d. impression ans: a- _________ is an electronic instrument used to show both the carrier and the sidebands of a modulated signal in the frequency domain. a. Spectrum analyzer b. Oscilloscope c. Digital counter d. Frequency counter ans: a- What part of the carrier is varied by the intelligence during modulation in an AM system? a. Phase b. Frequency c. Amplitude d. Phase and amplitude ans: c- The difference between the RF carrier and the modulating signal frequencies is called the a. USB b. LSB c. Sideband d. Carrier frequency ans: b- What stage in a radio transmitter isolates the oscillator from the load? a. Oscillator b. Buffer c. Separator d. Mixer ans: b- The frequency of the unmodulated carrier in FM system is a. modulating frequency b. center frequency c. carrier frequency d. deviation frequency ans: b- The ratio of maximum deviation to the maximum modulating frequency is called a. carrier swing b. deviation ratio c. modulation factor d. modulation index ans: b- A carrier signal has a. constant amplitude b. a frequency of 20 kHz and above c. a varying amplitude d. the information content ans: b- The modulated peak value of a signal is 125 V and the unmodulated carrier value is 85 V. What is the modulation index? a. 0.47 b. 0.68 c. 0.32 d. 1.47 ans: d- An 891 kHz carrier having an amplitude of 80 V is modulated by a 4.5 kHz audio signal having an amplitude of 45 V.. The modulation factor is a. 0.56 b. 0.65 c. 1.78 d. 1.25 ans: a- What is the modulation index of an FM signal having a carrier swing of 75 kHz when the modulating signal has frequency of 3 kHz? a. 25 b. 12.5 c. 0.04 d. 0.08 ans: b- In a FM system, if modulation index is doubled by halving the modulating frequency, what will be the effect on the maximum deviation? a. No effect b. Maximum deviation doubles c. Decreases by 1/2 d. Increases by 1/4 ans: a- Which of the following is considered as an indirect method of generating FM? a. Reactance modulator b. Balanced modulator c. Varactor diode modulator d. Armstrong system ans: d- To generate an SSB or DSB signal one must use a circuit known as a. filter modulator b. ring modulator c. balanced modulator d. reactance modulator ans: c- Which is the first radio receiver? a. TRF receiver b. Superheterodyne receiver c. Crystal radio receiver d. Heterodyne receiver ans: c- An interfering signal with a frequency equal to the received signal plus twice the IF is called a. image frequency b. center frequency c. rest frequency d. interference frequency ans: a- Double sideband full carrier emission type. a. A3J b. H3E c. R3A d. A3E ans: d- Single sideband reduced carrier emission type. a. H3E b. R3E c. J3E d. B8E ans: b- A single sideband suppressed carrier emission type. a. H3E b. R3E c. J3E d. B8E ans: c- Independent sideband emission type. a. H3E b. R3E c. J3E d. B8E ans: d- Vestigial sideband emission type a. C3F b. J3E c. R3E d. B8E ans: a- Single sideband full carrier emission type. a. R3E b. H3E c. J3E d. B8E ans: b- Phase modulation emission type. a. F3E b. F3C c. F3F d. G3E ans: d- Which one is not an advantage of SSB over AM? a. Power saving b. Requires half the bandwidth c. Wider area of reception d. Better fidelity ans: d- The advantage of a high level modulated AM transmitter is a. less audio power required b. better fidelity c. higher value of operating power d. less distortion ans: c- The advantage of a low-level modulated AM transmitter is a. less audio power required b. better fidelity c. higher value of operating power d. less distortion ans: a- _________ is the bad effect caused by overmodulation in AM transmission. a. Increase in noise b. Deviation in the operating frequency c. Interference to other radio services d. Decrease in the output power ans: c- Which characteristic of a radio receiver refers to its ability to reject an unwanted signal? a. Sensitivity b. Selectivity c. Fidelity d. Quality ans: b- What type of emission is frequency modulation? a. F3E b. G3E c. A3E d. B3E ans: a- AM transmission power increases with ________. a. frequency b. source c. load d. modulation ans: d- ________ locks the FM receiver to a stronger signal. a. Hall effect b. Capture effect c. Image frequency d. Homing ans: b- What is the highest percentage of modulation for AM? a. 50 % b. 75 % c. 100 % d. 80 % ans: c- In FM, the Carson's Rule states that the bandwidth is equal to twice the sum of the modulating frequency and _______. a. carrier signal b. modulating index c. frequency deviation d. image frequency ans: c- What is the carrier swing of an FM transmitter when modulated by 75 %? a. 53.2 kHz b. 48 kHz c. 56.25 kHz d. 112.5 kHz ans: d- The modulation system inherently more resistant to noise. a. Single sideband suppressed carrier b. Frequency modulation c. Pulse-position modulation d. Amplitude shift keying ans: b- Subcarriers that are arranged so that the channels occupying adjacent frequency bands with some frequency space between them is known as a. guard bands b. AM bands c. band gap d. void band ans: a- Modulation of an RF carrier results in a. multiple channels b. smaller antennas c. directional propagation d. all of the above ans: d- A process which occurs in the transmitter. a. Mixing b. Modulation c. Heterodyning d. Demodulation ans: b- A process which occurs in the receiver. a. Beating b. Modulation c. Mixing d. Demodulation ans: d- One part of the transmitter that protects the crystal oscillator from "pulling". a. Buffer amplifier b. Modulator c. Power amplifier d. Antenna coupler ans: a- What aspect of the carrier is changed by modulation? a. Frequency b. Phase c. Amplitude d. Depends on the type of modulation ans: d- The amplitude of a sine wave which is modulated by a musical program will a. be complex b. contain fundamental frequencies c. contain harmonic frequencies d. all of the above ans: d- What will be the result of the gain level being too high for signals entering the modulator? a. Receiver noise b. Excessive volume of receiver output c. Oscillator disturbance d. Distortion and splatter ans: d- Amplitude modulation causes the amount of transmitter power to a. increase b. decrease c. remain the same d. double ans: a- When a carrier is modulated 100%, the total power increases by what percentage over that of the carrier alone? a. 25 % b. 50 % c. 75 % d. 100 % ans: b- When the amplitude of the modulating voltage is increased for AM, the antenna current will a. increase b. decrease c. remain constant d. decrease exponentially ans: a- An increase in transmitter power from 25 W to 30 W will cause the antenna current to increase from 700 mA to a. 800 mA b. 750 mA c. 767 mA d. 840 mA ans: c- A second modulating tone having the same amplitude but a different frequency is added to the first at the input to the modulator. The modulation index will be increased by a factor of a. square root of 3 b. square root of 2 c. 2 d. 3 ans: b- A 1000 kHz carrier is modulated by a 2500 Hz tone. One frequency component of the modulated signal is a. 1200 Hz b. 5000 Hz c. 1002.5 kHz d. 2500 Hz ans: c- A 1200 kHz carrier is amplitude-modulated by two tones of 500 Hz and 700 Hz. Which one is a frequency component of the modulated wave? a. 1195 kHz b. 1199.3 kHz c. 1199.7 kHz d. 1205 kHz ans: b- Identify a modulation method, or methods in use for a common-emitter configuration. a. Base modulation b. Emitter modulation c. Collector modulation d. Both A and C ans: d- The RF signal injected into a balanced modulator is 10 MHz and the modulating frequency is 1 kHz. Which frequency, or frequencies, will not appear in the output? a. 9.999 MHz b. 10 MHz c. 10.0001 MHz d. both A and B ans: b- Unwanted sidebands in SSB equipment can be suppressed by one or more of the following methods. a. Phasing method b. Filter method c. Decoder method d. Both A and B ans: d- Envelope detection is concerned with the process of a. mixing b. heterodyning c. modulation d. rectification ans: d- Diagonal clipping in envelope detection will result in a. distortion b. phase reversal c. reduced sensitivity d. amplitude damage ans: a- Product detection requires the process of a. rectification b. heterodyning c. decoding d. phase shifting ans: b- A sine wave which is coherent with carrier has identical a. amplitude b. frequency c. phase angle d. both B and C ans: d- Frequency modulation and phase modulation are collectively referred to as a. stereo b. angle modulation c. high fidelity modulation d. FCC modulation ans: b- In FM the change in carrier frequency is proportional to what attribute of the modulating signal? a. angle b. frequency c. amplitude d. tone ans: c- A louder sound, when generating the modulating waveform for FM, will cause a greater a. carrier amplitude b. angle amplitude c. distortion at the receiver d. frequency deviation ans: d- If a positive change in modulation signal level of 200 mV will cause a positive frequency deviation of 10 kHz, what will be the frequency deviation for a negative change of 100 mV in the level of the modulating signals? a. 0 b. -5 kHz c. +5 kHz d. +0 kHz ans: b- A particular 15 kHz modulation tone results in a peak frequency deviation of 75 kHz. What is the modulation index? a. 5 b. 15 c. 75 d. 3 ans: a- A 15 kHz sine wave frequency-modulates an 88 MHz carrier. A sideband frequency will be found at a. 87.970 MHz b. 87.985 MHz c. 88.015 MHz d. All of these ans: d- A device whose capacitance is deliberately made to be a function of the applied voltage. a. Varactor diode b. UJT c. SAW d. Variable capacitor ans: a- A reactance modulator is one method of obtaining a. indirect FM b. direct FM c. demodulation d. low frequency filtering ans: b- A device, now available in IC form, is useful for direct FM and as one element in the phase-locked loop. a. AFC b. AGC c. VCO d. LPF ans: c- ________ is a frequency change process, whereby the phase deviation and frequency deviation are multiplied by some fixed constant. a. Translation b. Multiplication c. Division d. Addition ans: b- A circuit that has the function of demodulating the frequency-modulated signal. a. AFC b. Envelope detector c. Decoder d. Foster-Seeley discriminator ans: d- The ratio detector is superior to the slope detector because a. it is less sensitive to phase modulation b. it is less sensitive to noise spikes c. it is less sensitive to interference causing AM d. Both B and C ans: d- One implementation of a pulse-averaging discriminator is a. a free-running multivibrator b. a crystal-controlled oscillator c. a quartz crystal filter d. a triggered multivibrator ans: d- A 10% increase in the frequency of a constant-width pulse train should cause what change in its average value? a. -10% b. -1% c. +1% d. +10% ans: d- Two different signals can be coherent if they a. have the same amplitude b. are both sine waves of different frequencies c. originate in the same physical equipment simultaneously d. have the same frequency ans: d- A quadrature detector requires that a. four gates be provided b. the inputs are coherent c. the inputs are incoherent d. the inputs are identical ans: b- In a phase-locked loop, the VCO is the abbreviation for a. Variable coherent output b. VHF communication oscillator c. Voltage-controlled oscillator d. Vien-count oscillator (neutralized) ans: c- Identify an advantage , or advantages, of a properly designed FM system. a. Relative immunity to atmospheric noise (lightning) b. Reduced bandwidth required c. No noise of any kind d. The noise figure is inversely proportional to the modulation index. ans: a- The output of a balanced modulator a. LSB and USB b. LSB c. USB d. Carrier ans: a- If the modulation index of an AM wave is changed from 0 to 1, the transmitted power is a. unchanged b. halved c. doubled d. increased by 50% ans: d- Which of the following is not a baseband signal of modulation? a. Audio signal b. Video signal c. RF carrier d. Binary coded pulses ans: c- If the unmodulated level peak carrier amplitude is doubled in and AM signal, the percent modulation is ___________. a. 20 b. 50 c. 100 d. 200 ans: c- Balanced modulator circuit when inserted in the equipment suppresses the _________. a. carrier b. upper sideband c. lower sideband d. baseband signal ans: a- The carrier of a 100% modulated AM wave is suppressed, the percentage power saving is _________. a. 100 % b. 50 % c. 83 % d. 66.66 % ans: d- If the modulation index of an AM wave is doubled, the antenna current is also doubled, the AM system being used is a. H3E b. J3E c. C3F d. A3E ans: b- 100 % modulation in AM means a corresponding increase in total power by _________. a. 100 % b. 50 % c. 75 % d. 25 % ans: b- A single-tone amplitude modulated wave has _________. a. 2 components b. 3 components c. 4 components d. 2n + 1 components ans: b- A carrier signal has ____________. a. constant peak amplitude b. frequency range of 20-20,000 Hz c. a varying amplitude d. the information ans: a- The modulating system is ___________ if the modulating frequency is doubled, the modulation index is halved, and the modulating voltage remains constant. a. amplitude modulation b. phase modulation c. frequency modulation d. pulse modulation ans: c- What is the modulation index of an FM signal if its modulating frequency is doubled? a. No effect b. Twice the original index c. Four times the original index d. One-half the original index ans: d- An AM transmitter is rated 1000 W at 100 % modulation. How much power required for the carrier? a. 1000 W b. 666.6 W c. 333.3 W d. 866.6 W ans: b- Standard way of designating AM. a. A3E b. B3E c. AHE d. C3F ans: a- __________ is the circuit used to detect frequency modulated signal. a. Discriminator b. Modulator c. Modem d. Detector ans: a- __________ is an information signal that is sent directly without modulating any carrier. a. C-band b. Q-band c. Baseband d. Broadband ans: c- Both frequency and phase modulation utilize __________ modulation. a. digital b. phase c. amplitude d. angle ans: d- It is the width of frequencies within the spectrum occupied by a signal and used by the signal for conveying information. a. Band b. Bandwidth c. Electronic spectrum d. Frequency band ans: b- Which transmit only one sideband? a. H3E b. C3F c. A3E d. B8E ans: a- __________ is a kind of modulation in which the modulated wave is always present. a. Carrier modulation b. Continuous modulation c. Log-periodic modulation d. Square-wave modulation ans: b- A type of modulation in which no signal is present between pulses. a. Pulse modulation b. FSK c. QAM d. PAM ans: a- What describes the amount of amplitude change present in an AM waveform? a. Percent modulation b. Modulation constant c. Envelope of modulation d. Coefficient of modulation ans: d- __________ is a form of amplitude distortion introduced when the positive and negative alternations in the AM modulated signals are not equal. a. Envelope distortion b. Spurious emission c. Carrier shift d. Johnson noise ans: c- What is the advantage of phase modulation over direct FM frequency modulation? a. Multipliers can be used b. The deviation is smaller c. Simplicity and practicality d. The oscillator is crystal-controlled ans: d- If the spectrum is shifted in frequency with no other changes, this is known as a. frequency multiplication b. sideband movement c. baseband reorientation d. frequency translation ans: d- A device which is capable of causing frequency translation a. High-Q tank circuit b. Balanced modulator c. Low-Q tank circuit d. 1F strip ans: b- If the frequency of each component in a signal spectrum is increased by the same fixed amount, this is known as a. modulation b. frequency translation c. up conversion d. both B and C ans: d- A particular amplifier is designed to be a frequency doubler. If the input signal frequency is 15.4 MHz, a circuit in the output will be tuned to a. 7.7 MHz b. 15.4 MHz c. 30.8 MHz d. 61.6 MHz ans: c- A sine wave of 293 MHz is phase-modulated to achieve a maximum phase deviation of 0.2 radian. After passing through a frequency tripler, the maximum phase deviation will be a. 0.2 radian b. 0.3 radian c. 0.4 radian d. 0.6 radian ans: d- Any device to be used as a frequency multiplier must be a. active b. passive c. linear d. nonlinear ans: d- A particular amplifier circuit used for frequency doubling. a. Push-push b. Push-pull c. Pull-push d. Pull-pull ans: a- Frequency division is useful in the implementation of a a. AM demodulator b. frequency synthesizer c. AGC circuit d. FM demodulator ans: b- Frequency division by 12 will require how many flip-flops in the counter? a. 3 b. 4 c. 6 d. 12 ans: b- Identify an electronic device, not specifically designed for the purpose, which can be used as a phase detector. a. Wien bridge b. Colpitts oscillator c. Balanced modulator d. Butterworth filter ans: c- A particular frequency synthesizer contains only a single crystal. What words describe this synthesizer? a. Crystal modulated b. Inexact c. Indirect d. Deficient ans: c- A recognizable feature of a CW transmitter is a. Keyed transmitter b. Power amplification c. Frequency generation d. All of these ans: d- The term "pulling" refers to a. the change of the crystal oscillator frequency by loading b. one half-cycle operation of a push-pull amplifier c. loading on the transmitter caused by the antenna connection d. reduction of the power supply terminal voltage as the transmitter is keyed. ans: a- When frequency modulation is achieved by initial phase modulation, this is called a. angular modulation b. direct FM c. indirect FM d. indirect synthesis ans: c- A disadvantage of direct FM is the need for a. AGC b. AFC c. a frequency synthesizer d. phase modulation ans: b- Direct FM can be achieved by a. a reactance tube modulator b. a varactor diode c. an AGC circuit d. both A and B ans: d- A receiver in which all RF amplifier stages require manual tuning to the desired RF is called a. superheterodyne b. autodyne c. TRF d. AFC ans: c- Why is it often necessary to precede the demodulator by amplifier stages in a receiver? a. To improve fidelity b. To reduce receiver noise c. To eliminate image response d. To amplify weak antenna signals ans: d- A serious disadvantage of the TRF receiver a. Bandwidth variations over the tuning range b. The weight and cost c. The requirements for a closely regulated power supply d. The requirements for a half-wave antenna ans: a- Identify which is not a part of a superheterodyne receiver. a. Local oscillator b. Modulator c. IF amplifier d. Demodulator ans: b- Which major element will not be found in every superheterodyne receiver? a. R-F amplifier b. Mixer c. Local oscillator d. IF amplifier ans: a- Which major element of a superheterodyne receiver must be nonlinear? a. R-F amplifier b. Mixer c. Local oscillator d. IF amplifier ans: b- The change of the modulated carrier frequency from the original RF to the I-F of the superheterodyne receiver is known as a. frequency multiplication b. frequency allocation c. frequency substitution d. frequency translation ans: d- The key to achieving receiver sensitivity is the reduction of a. image response b. mixer harmonic products c. spurious frequency response d. internal noise ans: d- Which of the following receiver design objectives is not impossible? a. Elimination of galactic noise b. Elimination of atmospheric noise c. Elimination of man-made noise d. Reduction of receiver internal noise ans: d- In comparing the S/N ratio for the input to the receiver with the S/N ratio for the output, the latter is a. smaller b. the same c. greater d. infinite ans: a- The characteristic of a receiver that specifies the self-generated noise. a. Noise immunity b. Noise factor c. Noise figure d. Noise margin ans: c- An FM receiver with an I-F of 10.7 MHz is tuned to 98.7 MHz. What is the numerical value of the image frequency? a. 77.3 MHz b. 88.0 MHz c. 109.4 MHz d. 120.1 MHz ans: d- A source of RF interference exists at 109.9 MHz. For which frequency in the FM broadcast band will this be the image frequency? a. 21.4 MHz b. 88.5 MHz c. 99.2 MHz d. 110.7 MHz ans: b- The ratio of the superheterodyne receiver response at the desired carrier frequency to that at the image frequency is called a. the sensitivity b. the selectivity c. the image frequency d. the image rejection ratio ans: d- The core of an IF transformer usually contains a. teflon b. computer nylon c. powdered iron d. laminated steel ans: c- Shape factor is a measure of a. bandwidth b. skirt steepness c. coupling coefficient d. critical coupling ans: b- __________ is the function which tends to maintain the sound volume level of a voice receiver nearly constant for a large signal strength range. a. Squelch b. Muting c. AGC d. AFC ans: c- The function which tends to silence the receiver in the absence of transmitted carrier a. Squelch b. Muting c. AGC d. AFC ans: a- What device is incorporated in a communications receiver to reduce impulse noise? a. Front-end processor b. Squelch circuit c. AGC d. Noise blanker ans: d- What type of signal in which a receiver selectivity of 2.4 kHz in the I-F circuitry is optimum? a. FM voice b. Double-sideband AM voice c. FSK data d. SSB voice ans: d- If the input to a detector stage is an amplitude-modulated (A3E) IF signal then the output from the stage is a. a lower frequency carrier b. the audio voice information c. a morse-code signal d. the upper or lower set of sidebands ans: b- In a capacitive type, reactance-tube modulator connected across in oscillator tuned circuit, a more negative voltage on the grid of the reactance tube will cause a. an increase of the oscillator frequency b. a decrease of oscillator frequency c. an increase of the reactance-tube capacitance d. an increase of the reactance tube, ac plate current ans: a- The limiting condition for sensitivity in a communications receiver is a. the noise floor of the receiver b. the power-supply output ripple c. the two-tone intermodulation distortion d. the input impedance to the detector ans: a- When a communications receiver is tuned to a strong signal, the AGC bias is measured and found to be zero. The fault cannot be caused by a/an a. defective IF stage b. defective local oscillator c. defective RF stage d. open circuit in the AGC's filter capacitor ans: d- The term used to refer to the condition where the signals from a very strong station are superimposed on other signals being received. a. Cross-modulation interference b. Intermodulation interference c. Receiver quieting d. Capture effect ans: a- The limiter stage of an FM receiver. a. behaves as a low-pass filter b. limits the amplitude of the IF signal to the required level c. behaves as a high-pass filter d. behaves as a bandstop filter ans: b- Motorboating (low-frequency oscillations) in an amplifier can be stopped by a. grounding the screen grid b. connecting a capacitor between the B+ and lead ground c. by passing the screen grid resistor with a 0.1 uF capacitor d. grounding the plate ans: b- An effect in which, the modulation of an unwanted signal is transferred to the desired carrier a. Crossmodulation b. intermodulation c. Modulation mixing d. Image-channel interference ans: a- Leads should be kept as short as possible in radio circuit so that a. skin effect is reduced b. there is less hysteresis effect c. there is less dielectric loss d. stray coupling is minimized ans: d- The number of voice transmissions that can be packed into a given frequency band for amplitude-compandored single-sideband systems over conventional FM-phone systems. a. 2 b. 8 c. 16 d. 4 ans: d- Neutralization of an RF amplifier stage can be necessary in order to a. increase the amplifier's gain b. prevent the generation of spurious oscillations c. reduce the amplifier's gain d. reduce the level of the output harmonics ans: b- The ability of a communications receiver to perform well in the presence of strong signals outside the band of interest is indicated by what parameter? a. Blocking dynamic range b. Noise figure c. Signal-to-noise ratio d. Audio output ans: a- Stages that are common to both AM and FM receivers. a. tuner, local oscillator, detector, AF amplifier b. RF amplifier, mixer, IF amplifier, AF amplifier c. local oscillator, RF amplifier, frequency discriminator, detector d. tuner, IF amp, detector, AF amp ans: b- Occurs during CW reception if too narrow a filter bandwidth is used in the IF stage of a receiver a. Filter ringing b. Undesired signals will reach the audio stage c. Output-offset overshoot d. Cross-modulation distortion ans: a- What stage mainly determines a communication receiver's sensitivity? a. IF amplifier b. Mixer stage c. Detector stage d. RF amplifier ans: a- What is the main advantage of FM over AM? a. Better signal-to-noise ratio b. Narrower bandwidth c. Greater propagation range d. Total freedom from adjacent-channel interference ans: a- An amplitude modulation created in an amplifier before the final RF stage. a. Low-level modulation b. High-level modulation c. Direct modulation d. Indirect modulation ans: a- Receiver desensitizing can be reduced by a. increasing the transmitter audio gain b. decreasing the receiver squelch gain c. increasing the receiver bandwidth d. ensuring good RF shielding between the transmitter ans: d- In a narrow-band FM system, the deviation ratio is commonly one and the highest audio frequency is generally limited to a. 300 Hz b. 10,000 Hz c. 3,000 Hz d. 7,500 Hz ans: c- A type of emission is produced when an amplitude modulated transmitter is modulated by a facsimile signal. a. A3F b. F3F c. A3C d. F3C ans: c- Where is the noise generated which primarily determines the signal to noise ratio in a VHF (150 MHz) marine band receiver? a. In the detector b. In the atmosphere c. In the ionosphere d. In the receiver front end ans: d- Cross-modulation in a receiver can be reduced by a. installing a filter at the receiver b. using a filter at the receiver c. increasing the receiver's RF gain while decreasing the AF d. adjusting the pass-band tuning ans: a- What is the emission designation for FM telephony? a. F3E b. G3E c. J3E d. H3E ans: a- What is the cause of receiver desensitizing? a. The presence of a strong signal on a nearby frequency b. Audio gain adjusted too low c. Squelch gain adjusted too high d. Squelch gain adjusted too low ans: a- In a phase-modulated signal (indirect FM), the frequency deviation is directly proportional to the a. carrier amplitude only b. amplitude of the modulating tone and frequency of the carrier c. carrier frequency only d. modulating signal amplitude only ans: b- An RF stage precedes the mixer stage in a superhet receiver. One advantage of including this RF stage is a. better selectivity b. better rejection ratio c. greater sensitivity d. improved signal-to-noise ratio ans: b- Two factors that determine the sensitivity of a receiver. a. Dynamic range and third-order intercept b. Cost and availability c. Bandwidth and noise figure d. Intermodulation distortion and dynamic range ans: c- What is an undesirable effect of using too-wide a filter bandwidth in the IF section of a receiver? a. Undesired signals will reach the audio stage b. Output-offset overshoot c. Thermal-noise distortion d. Filter ringing ans: a- A system containing a limiter stage, a discriminator, and a de-emphasis circuit? a. Direct FM transmitter b. Indirect FM transmitter c. Single sideband AM receiver d. FM receiver ans: d- The limiter stage of an FM receiver a. prevents any amplitude modulation of the IF signal b. limits the amount of frequency deviation in the IF signal c. limits the overall bandwidth of the IF stages d. corrects any deviation in carrier frequency ans: a- High selectivity occurs when the degree of coupling between a receiver's RF stages is a. tight b. loose c. critical d. adjusted for maximum power transfer ans: b- A carrier is phase modulated by a test tone. If the amplitude and the frequency of the tone are both doubled, the amount of the deviation is a. doubled b. unchanged c. halved d. multiplied by four ans: d- The degree of selectivity desirable in the IF circuitry of a single-sideband receiver. a. 1 kHz b. 2.4 kHz c. 4.2 kHz d. 4.8 kHz ans: b- The base in an RF amplifier is grounded in order to a. avoid the requirement of neutralizing the stage b. raise the input impedance c. lower the output impedance d. obtain maximum power output ans: a- The AM detector performs two basic functions in the receiver. a. Rectifies and filters b. Amplifiers and filters c. Buffer and amplifier d. Buffer and detector ans: a- A varactor diode can be used in a/an a. direct FM modulator circuit b. AFC circuit in a direct FM transmitter c. phase-modulator circuit d. all of these ans: d- Receiver interference is not reduced by including a/an a. crystal filter b. insulating enclosures around the receiver c. wave trap d. RF stage ans: b- What is the emission C3F? a. RTTY b. SSB c. Television d. Modulated CW ans: c- What is the approximate dc input power to a class AB RF power amplifier stage in an unmodulated carrier transmitter when the PEP output is 500 W? a. Approximately 1000 W b. Approximately 800 W c. Approximately 250 W d. Approximately 600 W ans: a- Which of the following stages in an FM receiver is responsible for drastically reducing the effect of static noise during the reception of a signal? a. De-emphasis circuit b. Mixer stage c. Squelch circuit d. Limiter stage ans: d- The letters "SSSC" stand for a. single sideband, single carrier b. suppressed sideband, single channel c. suppressed sideband, single carrier d. single sideband, suppressed carrier ans: d- For many types of voices, what is the ratio of PEP-to-average power during a modulation peak in a single-sideband phone signal? a. Approximately 1.0 to 1 b. Approximately 25 to 1 c. Approximately 100 to 1 d. Approximately 2.5 to 1 ans: d- In most mixers, the oscillator frequency is ______ than the carrier frequency of he input signal. a. higher b. lower c. the same d. 10 kHz above ans: a- Features of a transmitter's buffer stage include a. high gain b. harmonic generation c. improvement in frequency stability of the oscillator d. low input impedance ans: c- Type of emission produced when an amplitude modulated transmitter is modulated by a television signal. a. F3F b. A3C c. F3C d. A3F ans: d- A pi-network is a. a network consisting entirely of four inductors or four capacitors b. a power incidence network c. an antenna matching network that is isolated from ground d. a network consisting of one inductor and two capacitors ans: d- How is a G3E FM-phone signals produced? a. A network consisting modulator on the audio amplifier b. With a reactance modulator on the final amplifier c. With a reactance modulator on the oscillator d. With a balanced modulator on the oscillator ans: c- A way of eliminating auto interference to radio reception a. Installing resistive spark plugs b. Installing capacitive spark plugs c. Installing resistors in series with the spark plugs d. Installing two copper-braid ground strips ans: a- The carrier in an AM transmitter is the a. transmitter's output signal when the modulation is zero b. transmitter's output signal when the modulation is present c. output signal from the crystal oscillator d. RMS value of the AM signal ans: a- What stage feeds the discriminator of an FM receiver? a. Local oscillator b. Mixer stage c. Final IF amplifier, which also acts as a limiter stage d. Buffer ans: c- In an FM receiver, the stage that has the IF signal as input and the audio signal as output. a. Limiter b. Audio amplifier c. IF amplifier d. Discriminator ans: d- What is capture effect? a. All signals on a frequency are demodulated by an FM receiver b. The loudest signal received is the only demodulated signal c. All signals on a frequency are demodulated by an AM receiver d. The weakest signal received is the only demodulated signal ans: b- A double-sideband phone signal can be generated by a. feeding a phase-modulated signal into a low-pass filter b. modulating the plate voltage of a class-C amplifier c. using a balanced modulator followed by a filter d. detuning a Hartley oscillator ans: b- Pre-emphasis is used in FM transmitters to improve the signal-to-noise ratio of a. high modulating frequencies b. low modulating frequencies c. all modulating frequencies d. frequency carrier ans: a- The result of cross-modulation is that a. the modulation of an unwanted signal is heard on the desired signal b. a decrease in modulation level of transmitted signals c. a receiver quieting d. of inverting sidebands in the final stage of the amplifier ans: a- Which of the following contains de-emphasis circuit? a. FM transmitter b. FM receiver c. VHF transmitter d. VHF receiver ans: b- What is emission F3F? a. AM b. Facsimile c. Television d. RTTY ans: c- What type of emission is produced when a frequency modulated transmitter is modulated by a facsimile signal? a. F3C b. A3C c. F3F d. A3F ans: a- Two AM transmitting antennas are close together. As a result the two modulated signals are mixed in the final RF stage of both transmitters. What is the resultant effect on the other station? a. Harmonic interference b. Intermodulation interference c. Spurious interference d. Crossmodulation interference ans: b- The term used to refer to the reduction of receiver gain caused by the signal or a nearby station transmitter in the same frequency band? a. Quieting b. Cross-modulation interference c. Squelch gain rollback d. Desensitizing ans: d- What is the bandwidth occupied by the carrier, both sidebands and harmonics? a. Authorized bandwidth b. Bandwidth of emission and occupied bandwidth c. Operating bandwidth d. All of these ans: b- A class-C RF amplifier is collector amplitude modulated and its average dc level collector current does not change. This means a. a normal condition b. excessive drive to the base c. insufficient drive to the base d. insufficient audio modulation ans: a- What determines the percentage modulation of an FM transmitter? a. Amplitude of the carrier b. Modulating frequency c. Carrier frequency d. Amplitude of the modulating signal ans: d- Deviation ratio of an FM transmitter is the ratio of the a. maximum frequency swing to the highest modulating frequency b. operating frequency of the assigned frequency c. frequency swing to the modulating frequency d. highest modulating frequency to the minimum frequency ans: a- The main purpose of the beat frequency oscillator (BFO) is to generate a. a 1 kHz not for morse reception b. aid in the reception of weak voice-modulated signals c. an output, whose frequency differs from the IF by 1 kHz d. a signal, whose frequency is the same as the intermediate frequency ans: c- Normally, a linear class B RF power amplifier operates with a bias approximately equal to a. twice cut-off b. ten times cut-off value c. 50 % of cut-off value d. projected cut-off ans: d- The purpose why an RF amplifier is operated under linear class-B conditions (as opposed to class-C) is to a. generate only even harmonics b. generate only odd harmonics c. increase the efficiency d. amplify an AM signal ans: d- The term used to refer to the condition where the signal from a very strong station are superimposed on other signal being received. a. Cross-modulation interference b. Intermodulation distortion c. Receiver quieting d. Capture effect ans: a- __________ is the amplitude of the maximum negative excursion of a signal as viewed on an oscilloscope. a. Peak-to-peak voltage b. Inverse peak positive voltage c. RMS voltage d. Peak negative voltage ans: d- The type of emission that suffer most from selective fading. a. CW and SSB b. SSB and TV c. FM and double sideband AM d. SSTV and CW ans: c- In an FM-phone signal, _______ is the ratio between the actual frequency deviation to the maximum frequency deviation. a. FM compressibility b. modulation index c. percentage of modulation d. quieting index ans: c- __________ is used to refer to the reception blockage of one FM-phone signal by another FM-phone signal. a. Capture effect b. Desensitization c. Cross-modulation interference d. Frequency discrimination ans: a- A receiver selectivity of 10 kHz in the IF circuitry is optimum for what type of signals? a. SSB voice b. Facsimile c. FM d. Double-sideband AM ans: d- If the envelope of modulation is constant in amplitude this means a. zero beat b. under-modulation c. zero-modulation d. over-modulation ans: c- What is the approximate bandwidth of an FM with a modulation factor of 12.5 and a modulating frequency of 10 kHz? a. 20 kHz b. 270 kHz c. 250 kHz d. 45 kHz ans: b- Amplitude modulation is the same as a. linear mixing b. analog multiplication c. signal summation d. multiplexing ans: a- The negative half of the AM wave is supplied by a/an _________ in a diode modulator. a. the tuned circuit b. transformer c. capacitor d. inductor ans: a- One of the following can produce AM. a. Having the carrier vary a resistance b. Having the modulating signal vary a capacitance c. Varying the carrier frequency d. Varying the gain of an amplifier ans: a- Amplitude modulators that vary the carrier amplitude with the modulating signal by passing it through an attenuator network is the principle of a. rectification b. amplification c. variable resistance d. absorption ans: c- Which component is used to produce AM at very high frequencies? a. Varactor diode b. Thermistor c. Cavity resonator d. PIN diode ans: d- A collector modulator has a supply voltage of 48 V. What is the peak-to-peak amplitude of the modulating signal for 100 percent modulation? a. 24 V b. 48 V c. 96 V d. 120 V ans: c- What circuit recovers the original modulating information from an AM signal? a. Modulator b. Demodulator c. Mixer d. Crystal set ans: b- What is most commonly used amplitude demodulator? a. Envelope detector b. Balanced modulator c. Mixer d. Crystal set ans: a- What circuit generates the upper and lower sidebands and suppresses the carrier? a. Amplitude moderator b. Diode detector c. Class C amplifier d. Balanced modulator ans: d- _________ is a widely used balanced modulator. a. Diode bridge circuit b. Full-wave bridge rectifier c. Lattice modulator d. Balanced bridge modulator ans: c- In a diode ring modulator, the diodes act like a. variable resistors b. switches c. rectifiers d. variable capacitors ans: b- The output of a balanced modulator is a. AM b. FM c. SSB d. DSB ans: d- The principal circuit in the popular 1496/1596 IC balanced modulator is a a. Differential amplifier b. Rectifier c. Bridge d. Constant current source ans: a- The most commonly used filter in SSB generators uses a. LC networks b. Mechanical resonators c. Crystals d. RC networks and op amps ans: c- In the phasing method of SSB generation, one sideband is canceled out due to a. phase shifting b. sharp selectivity c. carrier suppression d. phase inversion ans: a- A balanced modulator used to demodulate a SSB signal is called a/an a. transponder b. product detector c. converter d. remodulator ans: b- Frequency translation is done with a circuit called a a. summer b. multiplier c. divider d. mixer ans: d- Mixing for frequency conversion is the same as a. Rectification b. AM c. linear summing d. filtering ans: c- Which of the following is not a major advantage of FM over AM? a. Greater efficiency b. Noise immunity c. Capture effect d. Lower complexity and cost ans: d- The primary disadvantage of FM is its a. higher cost and complexity b. excessive use of spectrum space c. noise susceptibility d. lower efficiency ans: b- Noise is primarily a. high-frequency spikes b. low-frequency variations c. random level shifts d. random frequency variations ans: a- The receiver circuit that rids FM of noise is the a. modulator b. demodulator c. limiter d. low-pass filter ans: c- The AM signals generated at a low level may only be amplified by what type of amplifier? a. Class A b. Class B c. Class C d. All of these ans: c- SSB means a. Single sideband with suppressed carrier b. Single sideband with carrier c. Double sideband with no carrier d. Single sideband with reduced carrier ans: a- A circuit used to select the desired output from a mixer a. Transformer b. Resonant circuit c. Filter d. Phase-shift circuit ans: c- What is the output of a balanced modulator? a. AM b. DSB c. SSB d. ISB ans: b- The acronym SSSC refer to a. Suppressed sideband, single carrier b. Suppressed sideband, suppressed carrier c. Single sideband, suppressed carrier d. Single sideband, single carrier ans: c- Which process occurs in the receiver? a. Demodulation b. Reception c. Modulation d. Recreation ans: a- What is usually used to demodulate SSB or CW signal? a. PLL b. BFO c. Ratio detector d. All of these ans: b- Which of the following is the most widely used amplitude modulator? a. Diode detector b. PLL circuit c. VCO d. All of these ans: a- Which of the following is the most widely used balanced modulator? a. Full-wave bridge circuit b. Balanced bridge modulator c. Lattice modulator d. None of these ans: c