NYC RADIO REPAIR MECHANIC EXAM QUESTIONS AND CORRECT ANSWERS
(VERIFIED ANSWERS) PLUS RATIONALES
Question 1: What is the primary function of an RF choke in a radio frequency circuit?
A. To amplify high-frequency signals while suppressing low-frequency noise B. To pass
direct current while offering a high impedance to radio frequency alternating currents C. To
tune the receiver to a specific carrier frequency by varying capacitance D. To match the
output impedance of a transmitter to an unbalanced antenna feedline
CORRECT ANSWER: B. To pass direct current while offering a high impedance to radio
frequency alternating currents
Rationale: An RF choke is an inductor designed to block high-frequency alternating current
(AC) while allowing direct current (DC) or lower-frequency signals to pass through. Its high
inductive reactance at RF frequencies effectively isolates different stages of a circuit.
Question 2: Which test instrument is most appropriate for measuring the standing wave ratio
(SWR) of a transmission line connected to an antenna?
A. An oscilloscope B. A spectrum analyzer C. A directional wattmeter / SWR bridge D. A
digital multimeter in resistance mode
CORRECT ANSWER: C. A directional wattmeter / SWR bridge
Rationale: A directional wattmeter or SWR bridge measures forward and reflected power in
a transmission line, allowing technicians to calculate the Standing Wave Ratio to ensure
efficient power transfer and minimal signal reflection.
Question 3: In a superheterodyne receiver, what is the primary purpose of the intermediate
frequency (IF) stage?
A. To convert audio frequencies into radio frequency signals for transmission B. To provide
the majority of the receiver's gain and selectivity at a fixed frequency C. To generate the
local oscillator frequency required for mixing D. To demodulate the FM carrier into
baseband audio signals
CORRECT ANSWER: B. To provide the majority of the receiver's gain and selectivity at a fixed
frequency
Rationale: The IF stage operates at a constant, fixed frequency regardless of the incoming RF
signal. This allows optimized filter design and stable, high-gain amplification across the
entire tuning range of the receiver.
Question 4: What is the skin effect in electrical conductors at radio frequencies?
,A. The tendency of high-frequency current to flow primarily along the outer surface of a
conductor B. The reduction of conductor resistance due to magnetic field cancellation C. The
physical expansion of coaxial cables when exposed to high transmitter power D. The
degradation of insulation materials caused by ultraviolet radiation
CORRECT ANSWER: A. The tendency of high-frequency current to flow primarily along the
outer surface of a conductor
Rationale: Skin effect is caused by eddy currents induced by the alternating magnetic field
generated inside the conductor. At higher frequencies, current density is highest near the
surface, effectively reducing the cross-sectional area available for current flow and
increasing effective AC resistance.
Question 5: Which modulation scheme combines phase shift keying and amplitude shift keying
to transmit digital data efficiently?
A. Frequency Modulation (FM) B. Amplitude Modulation (AM) C. Quadrature Amplitude
Modulation (QAM) D. Single Sideband (SSB)
CORRECT ANSWER: C. Quadrature Amplitude Modulation (QAM)
Rationale: QAM varies both the amplitude and the phase of a carrier wave to encode digital
data, allowing for high data density within a given bandwidth.
Question 6: When servicing a two-way radio transmitter, what hazard is primarily associated
with high-voltage power amplifier vacuum tubes or final RF stages?
A. High levels of infrared radiation B. Exposure to lethal DC voltages, often exceeding
several hundred to thousands of volts C. Immediate chemical burns from electrolyte leakage
D. Severe acoustic trauma from high-frequency whistling
CORRECT ANSWER: B. Exposure to lethal DC voltages, often exceeding several hundred to
thousands of volts
Rationale: Transmitters utilizing vacuum tubes or high-power solid-state final amplifiers
operate with high-voltage DC power supplies that pose severe electrical shock or
electrocution hazards even after the equipment is powered off, due to charged filter
capacitors.
Question 7: What does a decibel (dB) measure in electronic communications?
A. Absolute power levels in watts relative to zero B. A logarithmic ratio between two power
or voltage levels C. The precise frequency stability of a crystal oscillator D. The physical
length of an antenna element relative to wavelength
CORRECT ANSWER: B. A logarithmic ratio between two power or voltage levels
,Rationale: The decibel is a dimensionless logarithmic unit used to express the ratio of two
values, such as power, voltage, or sound intensity, making it convenient for handling large
dynamic ranges in electronics.
Question 8: Which parameter of a coaxial cable indicates its characteristic impedance under
matched conditions?
A. The physical length of the cable in meters B. The ratio of distributed inductance to
distributed capacitance per unit length C. The DC resistance measured with an ohmmeter
between the center conductor and shield D. The maximum voltage breakdown rating of the
dielectric material
CORRECT ANSWER: B. The ratio of distributed inductance to distributed capacitance per unit
length
Rationale: Characteristic impedance ($Z_0$) is determined by the physical geometry and
materials of the cable, specifically the square root of the ratio of its inductance per unit
length to its capacitance per unit length ($Z_0 = \sqrt{L/C}$).
Question 9: What is the function of a squelch circuit in a communications receiver?
A. To automatically tune the receiver to the strongest nearby station B. To mute the audio
output when the received signal strength falls below a designated threshold C. To prevent
audio distortion caused by overmodulation of the transmitter D. To compress the dynamic
range of audio signals before transmission
CORRECT ANSWER: B. To mute the audio output when the received signal strength falls below
a designated threshold
Rationale: A squelch circuit eliminates the annoying static or background noise heard in a
receiver speaker when no valid signal is present by disabling the audio amplifier until an
adequate carrier is received.
Question 10: Which type of filter passes frequencies within a specific band while attenuating
frequencies above and below that band?
A. High-pass filter B. Low-pass filter C. Band-pass filter D. Notch filter
CORRECT ANSWER: C. Band-pass filter
Rationale: A band-pass filter allows signals within a specific frequency range to pass
unhindered while strongly attenuating any frequencies outside of that designated passband.
Question 11: What is the primary purpose of a Phase-Locked Loop (PLL) circuit in modern radio
transceivers?
, A. To convert analog voice signals into digital data streams B. To synthesize stable, precise,
and selectable local oscillator frequencies C. To automatically match antenna impedance
across multiple frequency bands D. To protect the final amplifier from excessive reflected
power
CORRECT ANSWER: B. To synthesize stable, precise, and selectable local oscillator frequencies
Rationale: A PLL uses a phase detector, loop filter, voltage-controlled oscillator (VCO), and
frequency divider to generate highly stable and agile frequencies derived from a single
reference crystal oscillator.
Question 12: How does thermal noise (Johnson-Nyquist noise) vary with bandwidth in a
receiving system?
A. It is inversely proportional to the square root of the bandwidth B. It is directly
proportional to the square root of the noise bandwidth C. It remains entirely independent of
bandwidth D. It increases exponentially with bandwidth
CORRECT ANSWER: B. It is directly proportional to the square root of the noise bandwidth
Rationale: Thermal noise power generated by a resistor is given by $P = kTB$ (where $k$ is
Boltzmann's constant, $T$ is temperature, and $B$ is bandwidth). Thus, noise voltage is
proportional to the square root of the bandwidth.
Question 13: What tool is essential for visualizing the frequency spectrum of an RF signal to
check for harmonics and spurious emissions?
A. Logic analyzer B. Spectrum analyzer C. Function generator D. LCR meter
CORRECT ANSWER: B. Spectrum analyzer
Rationale: A spectrum analyzer displays signal amplitude as a function of frequency, making
it the ideal instrument for identifying harmonic distortion, intermodulation products, and
spurious emissions in radio transmitters.
Question 14: What is the primary characteristic of an omnidirectional antenna?
A. It radiates and receives radio frequency energy equally well in all horizontal directions B.
It focuses all transmitted power into a very narrow beam toward a specific horizon C. It only
operates effectively at frequencies below 300 kHz D. It requires an active DC power source
mounted at the antenna mast
CORRECT ANSWER: A. It radiates and receives radio frequency energy equally well in all
horizontal directions
(VERIFIED ANSWERS) PLUS RATIONALES
Question 1: What is the primary function of an RF choke in a radio frequency circuit?
A. To amplify high-frequency signals while suppressing low-frequency noise B. To pass
direct current while offering a high impedance to radio frequency alternating currents C. To
tune the receiver to a specific carrier frequency by varying capacitance D. To match the
output impedance of a transmitter to an unbalanced antenna feedline
CORRECT ANSWER: B. To pass direct current while offering a high impedance to radio
frequency alternating currents
Rationale: An RF choke is an inductor designed to block high-frequency alternating current
(AC) while allowing direct current (DC) or lower-frequency signals to pass through. Its high
inductive reactance at RF frequencies effectively isolates different stages of a circuit.
Question 2: Which test instrument is most appropriate for measuring the standing wave ratio
(SWR) of a transmission line connected to an antenna?
A. An oscilloscope B. A spectrum analyzer C. A directional wattmeter / SWR bridge D. A
digital multimeter in resistance mode
CORRECT ANSWER: C. A directional wattmeter / SWR bridge
Rationale: A directional wattmeter or SWR bridge measures forward and reflected power in
a transmission line, allowing technicians to calculate the Standing Wave Ratio to ensure
efficient power transfer and minimal signal reflection.
Question 3: In a superheterodyne receiver, what is the primary purpose of the intermediate
frequency (IF) stage?
A. To convert audio frequencies into radio frequency signals for transmission B. To provide
the majority of the receiver's gain and selectivity at a fixed frequency C. To generate the
local oscillator frequency required for mixing D. To demodulate the FM carrier into
baseband audio signals
CORRECT ANSWER: B. To provide the majority of the receiver's gain and selectivity at a fixed
frequency
Rationale: The IF stage operates at a constant, fixed frequency regardless of the incoming RF
signal. This allows optimized filter design and stable, high-gain amplification across the
entire tuning range of the receiver.
Question 4: What is the skin effect in electrical conductors at radio frequencies?
,A. The tendency of high-frequency current to flow primarily along the outer surface of a
conductor B. The reduction of conductor resistance due to magnetic field cancellation C. The
physical expansion of coaxial cables when exposed to high transmitter power D. The
degradation of insulation materials caused by ultraviolet radiation
CORRECT ANSWER: A. The tendency of high-frequency current to flow primarily along the
outer surface of a conductor
Rationale: Skin effect is caused by eddy currents induced by the alternating magnetic field
generated inside the conductor. At higher frequencies, current density is highest near the
surface, effectively reducing the cross-sectional area available for current flow and
increasing effective AC resistance.
Question 5: Which modulation scheme combines phase shift keying and amplitude shift keying
to transmit digital data efficiently?
A. Frequency Modulation (FM) B. Amplitude Modulation (AM) C. Quadrature Amplitude
Modulation (QAM) D. Single Sideband (SSB)
CORRECT ANSWER: C. Quadrature Amplitude Modulation (QAM)
Rationale: QAM varies both the amplitude and the phase of a carrier wave to encode digital
data, allowing for high data density within a given bandwidth.
Question 6: When servicing a two-way radio transmitter, what hazard is primarily associated
with high-voltage power amplifier vacuum tubes or final RF stages?
A. High levels of infrared radiation B. Exposure to lethal DC voltages, often exceeding
several hundred to thousands of volts C. Immediate chemical burns from electrolyte leakage
D. Severe acoustic trauma from high-frequency whistling
CORRECT ANSWER: B. Exposure to lethal DC voltages, often exceeding several hundred to
thousands of volts
Rationale: Transmitters utilizing vacuum tubes or high-power solid-state final amplifiers
operate with high-voltage DC power supplies that pose severe electrical shock or
electrocution hazards even after the equipment is powered off, due to charged filter
capacitors.
Question 7: What does a decibel (dB) measure in electronic communications?
A. Absolute power levels in watts relative to zero B. A logarithmic ratio between two power
or voltage levels C. The precise frequency stability of a crystal oscillator D. The physical
length of an antenna element relative to wavelength
CORRECT ANSWER: B. A logarithmic ratio between two power or voltage levels
,Rationale: The decibel is a dimensionless logarithmic unit used to express the ratio of two
values, such as power, voltage, or sound intensity, making it convenient for handling large
dynamic ranges in electronics.
Question 8: Which parameter of a coaxial cable indicates its characteristic impedance under
matched conditions?
A. The physical length of the cable in meters B. The ratio of distributed inductance to
distributed capacitance per unit length C. The DC resistance measured with an ohmmeter
between the center conductor and shield D. The maximum voltage breakdown rating of the
dielectric material
CORRECT ANSWER: B. The ratio of distributed inductance to distributed capacitance per unit
length
Rationale: Characteristic impedance ($Z_0$) is determined by the physical geometry and
materials of the cable, specifically the square root of the ratio of its inductance per unit
length to its capacitance per unit length ($Z_0 = \sqrt{L/C}$).
Question 9: What is the function of a squelch circuit in a communications receiver?
A. To automatically tune the receiver to the strongest nearby station B. To mute the audio
output when the received signal strength falls below a designated threshold C. To prevent
audio distortion caused by overmodulation of the transmitter D. To compress the dynamic
range of audio signals before transmission
CORRECT ANSWER: B. To mute the audio output when the received signal strength falls below
a designated threshold
Rationale: A squelch circuit eliminates the annoying static or background noise heard in a
receiver speaker when no valid signal is present by disabling the audio amplifier until an
adequate carrier is received.
Question 10: Which type of filter passes frequencies within a specific band while attenuating
frequencies above and below that band?
A. High-pass filter B. Low-pass filter C. Band-pass filter D. Notch filter
CORRECT ANSWER: C. Band-pass filter
Rationale: A band-pass filter allows signals within a specific frequency range to pass
unhindered while strongly attenuating any frequencies outside of that designated passband.
Question 11: What is the primary purpose of a Phase-Locked Loop (PLL) circuit in modern radio
transceivers?
, A. To convert analog voice signals into digital data streams B. To synthesize stable, precise,
and selectable local oscillator frequencies C. To automatically match antenna impedance
across multiple frequency bands D. To protect the final amplifier from excessive reflected
power
CORRECT ANSWER: B. To synthesize stable, precise, and selectable local oscillator frequencies
Rationale: A PLL uses a phase detector, loop filter, voltage-controlled oscillator (VCO), and
frequency divider to generate highly stable and agile frequencies derived from a single
reference crystal oscillator.
Question 12: How does thermal noise (Johnson-Nyquist noise) vary with bandwidth in a
receiving system?
A. It is inversely proportional to the square root of the bandwidth B. It is directly
proportional to the square root of the noise bandwidth C. It remains entirely independent of
bandwidth D. It increases exponentially with bandwidth
CORRECT ANSWER: B. It is directly proportional to the square root of the noise bandwidth
Rationale: Thermal noise power generated by a resistor is given by $P = kTB$ (where $k$ is
Boltzmann's constant, $T$ is temperature, and $B$ is bandwidth). Thus, noise voltage is
proportional to the square root of the bandwidth.
Question 13: What tool is essential for visualizing the frequency spectrum of an RF signal to
check for harmonics and spurious emissions?
A. Logic analyzer B. Spectrum analyzer C. Function generator D. LCR meter
CORRECT ANSWER: B. Spectrum analyzer
Rationale: A spectrum analyzer displays signal amplitude as a function of frequency, making
it the ideal instrument for identifying harmonic distortion, intermodulation products, and
spurious emissions in radio transmitters.
Question 14: What is the primary characteristic of an omnidirectional antenna?
A. It radiates and receives radio frequency energy equally well in all horizontal directions B.
It focuses all transmitted power into a very narrow beam toward a specific horizon C. It only
operates effectively at frequencies below 300 kHz D. It requires an active DC power source
mounted at the antenna mast
CORRECT ANSWER: A. It radiates and receives radio frequency energy equally well in all
horizontal directions
