E4 Questions
59 questions in this subelement. Click any question ID for more details.
Answer: B
Which of the following parameters does a spectrum analyzer display on the vertical and horizontal axes?
ASignal amplitude and time
BSignal amplitude and frequency
CSWR and frequency
DSWR and time
Answer: B
Which of the following test instruments is used to display spurious signals and/or intermodulation distortion products generated by an SSB transmitter?
ADifferential resolver
BSpectrum analyzer
CLogic analyzer
DNetwork analyzer
Answer: A
How is compensation of an oscilloscope probe performed?
AA square wave is displayed, and the probe is adjusted until the horizontal portions of the displayed wave are as nearly flat as possible
BA high frequency sine wave is displayed, and the probe is adjusted for maximum amplitude
CA frequency standard is displayed, and the probe is adjusted until the deflection time is accurate
DA DC voltage standard is displayed, and the probe is adjusted until the displayed voltage is accurate
Answer: D
What is the purpose of using a prescaler with a frequency counter?
AAmplify low-level signals for more accurate counting
BMultiply a higher frequency signal so a low-frequency counter can display the operating frequency
CPrevent oscillation in a low-frequency counter circuit
DReduce the signal frequency to within the counter's operating range
Answer: A
What is the effect of aliasing on a digital oscilloscope when displaying a waveform?
AA false, jittery low-frequency version of the waveform is displayed
BThe waveform DC offset will be inaccurate
CCalibration of the vertical scale is no longer valid
DExcessive blanking occurs, which prevents display of the waveform
Answer: B
Which of the following is an advantage of using an antenna analyzer compared to an SWR bridge?
AAntenna analyzers automatically tune your antenna for resonance
BAntenna analyzers compute SWR and impedance automatically
CAntenna analyzers display a time-varying representation of the modulation envelope
DAll these choices are correct
Answer: D
Which of the following is used to measure SWR?
ADirectional wattmeter
BVector network analyzer
CAntenna analyzer
DAll these choices are correct
Answer: A
Which of the following is good practice when using an oscilloscope probe?
AMinimize the length of the probe's ground connection
BNever use a high-impedance probe to measure a low-impedance circuit
CNever use a DC-coupled probe to measure an AC circuit
DAll these choices are correct
Answer: D
Which trigger mode is most effective when using an oscilloscope to measure a linear power supply’s output ripple?
ASingle-shot
BEdge
CLevel
DLine
Answer: D
Which of the following can be measured with an antenna analyzer?
AVelocity factor
BCable length
CResonant frequency of a tuned circuit
DAll these choices are correct
Answer: A
What is the significance of voltmeter sensitivity expressed in ohms per volt?
AThe full scale reading of the voltmeter multiplied by its ohms per volt rating is the input impedance of the voltmeter
BThe reading in volts multiplied by the ohms per volt rating will determine the power drawn by the device under test
CThe reading in ohms divided by the ohms per volt rating will determine the voltage applied to the circuit
DThe full scale reading in amps divided by ohms per volt rating will determine the size of shunt needed
Answer: A
Which S parameter represents input port return loss or reflection coefficient (equivalent to VSWR)?
AS11
BS12
CS21
DS22
Answer: B
What three test loads are used to calibrate an RF vector network analyzer?
A50 ohms, 75 ohms, and 90 ohms
BShort circuit, open circuit, and 50 ohms
CShort circuit, open circuit, and resonant circuit
D50 ohms through 1/8 wavelength, 1/4 wavelength, and 1/2 wavelength of coaxial cable
Answer: D
How much power is being absorbed by the load when a directional power meter connected between a transmitter and a terminating load reads 100 watts forward power and 25 watts reflected power?
A100 watts
B125 watts
C112.5 watts
D75 watts
Answer: A
What do the subscripts of S parameters represent?
AThe port or ports at which measurements are made
BThe relative time between measurements
CRelative quality of the data
DFrequency order of the measurements
Answer: C
Which of the following can be used to determine the Q of a series-tuned circuit?
AThe ratio of inductive reactance to capacitive reactance
BThe frequency shift
CThe bandwidth of the circuit's frequency response
DThe resonant frequency of the circuit
Answer: B
Which of the following can be measured by a two-port vector network analyzer?
APhase noise
BFilter frequency response
CPulse rise time
DForward power
Answer: B
Which of the following methods measures intermodulation distortion in an SSB transmitter?
AModulate the transmitter using two RF signals having non-harmonically related frequencies and observe the RF output with a spectrum analyzer
BModulate the transmitter using two AF signals having non-harmonically related frequencies and observe the RF output with a spectrum analyzer
CModulate the transmitter using two AF signals having harmonically related frequencies and observe the RF output with a peak reading wattmeter
DModulate the transmitter using two RF signals having harmonically related frequencies and observe the RF output with a logic analyzer
Answer: D
Which of the following can be measured with a vector network analyzer?
AInput impedance
BOutput impedance
CReflection coefficient
DAll these choices are correct
Answer: A
Which of the following receiver circuits can be effective in eliminating interference from strong out-of- band signals?
AA front-end filter or preselector
BA narrow IF filter
CA notch filter
DA properly adjusted product detector
Answer: C
What is the term for the suppression in an FM receiver of one signal by another stronger signal on the same frequency?
ADesensitization
BCross-modulation interference
CCapture effect
DFrequency discrimination
Answer: D
What is the noise figure of a receiver?
AThe ratio of atmospheric noise to phase noise
BThe ratio of the noise bandwidth in hertz to the theoretical bandwidth of a resistive network
CThe ratio in dB of the noise generated in the receiver to atmospheric noise
DThe ratio in dB of the noise generated by the receiver to the theoretical minimum noise
Answer: B
What does a receiver noise floor of -174 dBm represent?
AThe receiver noise is 6 dB above the theoretical minimum
BThe theoretical noise in a 1 Hz bandwidth at the input of a perfect receiver at room temperature
CThe noise figure of a 1 Hz bandwidth receiver
DThe receiver noise is 3 dB above theoretical minimum
Answer: D
How much does increasing a receiver’s bandwidth from 50 Hz to 1,000 Hz increase the receiver’s noise floor?
A3 dB
B5 dB
C10 dB
D13 dB
Answer: B
What does the MDS of a receiver represent?
AThe meter display sensitivity
BThe minimum discernible signal
CThe modulation distortion specification
DThe maximum detectable spectrum
Answer: D
An SDR receiver is overloaded when input signals exceed what level?
AOne-half of the maximum sample rate
BOne-half of the maximum sampling buffer size
CThe maximum count value of the analog-to-digital converter
DThe reference voltage of the analog-to-digital converter
Answer: C
Which of the following choices is a good reason for selecting a high IF for a superheterodyne HF or VHF communications receiver?
AFewer components in the receiver
BReduced drift
CEasier for front-end circuitry to eliminate image responses
DImproved receiver noise figure
Answer: C
What is an advantage of having a variety of receiver bandwidths from which to select?
AThe noise figure of the RF amplifier can be adjusted to match the modulation type, thus increasing receiver sensitivity
BReceiver power consumption can be reduced when wider bandwidth is not required
CReceive bandwidth can be set to match the modulation bandwidth, maximizing signal-to-noise ratio and minimizing interference
DMultiple frequencies can be received simultaneously if desired
Answer: D
Why does input attenuation reduce receiver overload on the lower frequency HF bands with little or no impact on signal-to-noise ratio?
AThe attenuator has a low-pass filter to increase the strength of lower frequency signals
BThe attenuator has a noise filter to suppress interference
CSignals are attenuated separately from the noise
DAtmospheric noise is generally greater than internally generated noise even after attenuation
Answer: C
How does a narrow-band roofing filter affect receiver performance?
AIt improves sensitivity by reducing front-end noise
BIt improves intelligibility by using low Q circuitry to reduce ringing
CIt improves blocking dynamic range by attenuating strong signals near the receive frequency
DAll these choices are correct
Answer: D
What is reciprocal mixing?
ATwo out-of-band signals mixing to generate an in-band spurious signal
BIn-phase signals cancelling in a mixer resulting in loss of receiver sensitivity
CTwo digital signals combining from alternate time slots
DLocal oscillator phase noise mixing with adjacent strong signals to create interference to desired signals
Answer: C
What is the purpose of the receiver IF Shift control?
ATo permit listening on a different frequency from the transmitting frequency
BTo change frequency rapidly
CTo reduce interference from stations transmitting on adjacent frequencies
DTo tune in stations slightly off frequency without changing the transmit frequency
Answer: A
Which of the following describes problems caused by poor dynamic range in a receiver?
ASpurious signals caused by cross modulation and desensitization from strong adjacent signals
BOscillator instability requiring frequent retuning and loss of ability to recover the opposite sideband
CPoor weak signal reception caused by insufficient local oscillator injection
DOscillator instability and severe audio distortion of all but the strongest received signals
Answer: B
What creates intermodulation interference between two repeaters in close proximity?
AThe output signals cause feedback in the final amplifier of one or both transmitters
BThe output signals mix in the final amplifier of one or both transmitters
CThe input frequencies are harmonically related
DThe output frequencies are harmonically related
Answer: B
Which of the following is used to reduce or eliminate intermodulation interference in a repeater caused by a nearby transmitter?
AA band-pass filter in the feed line between the transmitter and receiver
BA properly terminated circulator at the output of the repeater’s transmitter
CUtilizing a Class C final amplifier
DUtilizing a Class D final amplifier
Answer: A
What transmitter frequencies would create an intermodulation-product signal in a receiver tuned to 146.70 MHz when a nearby station transmits on 146.52 MHz?
A146.34 MHz and 146.61 MHz
B146.88 MHz and 146.34 MHz
C146.10 MHz and 147.30 MHz
D146.30 MHz and 146.90 MHz
Answer: C
What is the term for the reduction in receiver sensitivity caused by a strong signal near the received frequency?
AReciprocal mixing
BQuieting
CDesensitization
DCross modulation interference
Answer: A
Which of the following reduces the likelihood of receiver desensitization?
AInsert attenuation before the first RF stage
BRaise the receiver’s IF frequency
CIncrease the receiver’s front-end gain
DSwitch from fast AGC to slow AGC
Answer: C
What causes intermodulation in an electronic circuit?
ANegative feedback
BLack of neutralization
CNonlinear circuits or devices
DPositive feedback
Answer: C
What is the purpose of the preselector in a communications receiver?
ATo store frequencies that are often used
BTo provide broadband attenuation before the first RF stage to prevent intermodulation
CTo increase the rejection of signals outside the band being received
DTo allow selection of the optimum RF amplifier device
Answer: C
What does a third-order intercept level of 40 dBm mean with respect to receiver performance?
ASignals less than 40 dBm will not generate audible third-order intermodulation products
BThe receiver can tolerate signals up to 40 dB above the noise floor without producing third-order intermodulation products
CA pair of 40 dBm input signals will theoretically generate a third-order intermodulation product that has the same output amplitude as either of the input signals
DA pair of 1 mW input signals will produce a third-order intermodulation product that is 40 dB stronger than the input signal
Answer: A
Why are odd-order intermodulation products, created within a receiver, of particular interest compared to other products?
AOdd-order products of two signals in the band being received are also likely to be within the band
BOdd-order products are more likely to overload the IF filters
COdd-order products are an indication of poor image rejection
DOdd-order intermodulation produces three products for every input signal within the band of interest
Answer: C
What is the link margin in a system with a transmit power level of 10 W (+40 dBm), a system antenna gain of 10 dBi, a cable loss of 3 dB, a path loss of 136 dB, a receiver minimum discernable signal of -103 dBm, and a required signal-to-noise ratio of 6 dB?
A-8dB
B-14dB
C+8dB
D+14dB
Answer: A
What is the received signal level with a transmit power of 10 W (+40 dBm), a transmit antenna gain of 6 dBi, a receive antenna gain of 3 dBi, and a path loss of 100 dB?
A-51 dBm
B-54 dBm
C-57 dBm
D-60 dBm
Answer: D
What power level does a receiver minimum discernible signal of -100 dBm represent?
A100 microwatts
B0.1 microwatt
C0.001 microwatts
D0.1 picowatts
Answer: D
Which of the following types of noise can often be reduced by a digital noise reduction?
ABroadband white noise
BIgnition noise
CPower line noise
DAll these choices are correct
Answer: B
Which of the following types of noise are removed by a noise blanker?
ABroadband white noise
BImpulse noise
CHum and buzz
DAll these choices are correct
Answer: D
How can conducted noise from an automobile battery charging system be suppressed?
ABy installing filter capacitors in series with the alternator leads
BBy installing a noise suppression resistor and a blocking capacitor at the battery
CBy installing a high-pass filter in series with the radio’s power lead and a low-pass filter in parallel with the antenna feed line
DBy installing ferrite chokes on the charging system leads
Answer: B
What is used to suppress radio frequency interference from a line-driven AC motor?
AA high-pass filter in series with the motor’s power leads
BA brute-force AC-line filter in series with the motor’s power leads
CA bypass capacitor in series with the motor’s field winding
DA bypass choke in parallel with the motor’s field winding
Answer: C
What type of electrical interference can be caused by computer network equipment?
AA loud AC hum in the audio output of your station’s receiver
BA clicking noise at intervals of a few seconds
CThe appearance of unstable modulated or unmodulated signals at specific frequencies
DA whining-type noise that continually pulses off and on
Answer: B
Which of the following can cause shielded cables to radiate or receive interference?
ALow inductance ground connections at both ends of the shield
BCommon-mode currents on the shield and conductors
CUse of braided shielding material
DTying all ground connections to a common point resulting in differential-mode currents in the shield
Answer: B
What current flows equally on all conductors of an unshielded multiconductor cable?
ADifferential-mode current
BCommon-mode current
CReactive current only
DMagnetically-coupled current only
Answer: C
What undesirable effect can occur when using a noise blanker?
AReceived audio in the speech range might have an echo effect
BThe audio frequency bandwidth of the received signal might be compressed
CStrong signals may be distorted and appear to cause spurious emissions
DFM signals can no longer be demodulated
Answer: D
Which of the following can create intermittent loud roaring or buzzing AC line interference?
AArcing contacts in a thermostatically controlled device
BA defective doorbell or doorbell transformer inside a nearby residence
CA malfunctioning illuminated advertising display
DAll these choices are correct
Answer: B
What could be the cause of local AM broadcast band signals combining to generate spurious signals on the MF or HF bands?
AOne or more of the broadcast stations is transmitting an over-modulated signal
BNearby corroded metal connections are mixing and reradiating the broadcast signals
CYou are receiving skywave signals from a distant station
DYour station receiver IF amplifier stage is overloaded
Answer: A
What causes interference received as a series of carriers at regular intervals across a wide frequency range?
ASwitch-mode power supplies
BRadar transmitters
CWireless security camera transmitters
DElectric fences
Answer: C
Where should a station AC surge protector be installed?
AAt the AC service panel
BAt an AC outlet
COn the single point ground panel
DOn a ground rod outside the station
Answer: D
What is the purpose of a single point ground panel?
ARemove AC power in case of a short-circuit
BPrevent common-mode transients in multi-wire systems
CEliminate air gaps between protected and non-protected circuits
DEnsure all lightning protectors activate at the same time