Wisconsin WI Communication System Specialty
Exam
**Question 1.** Which parameter directly determines the bandwidth of a sinusoidal RF carrier?
A) Amplitude
B) Frequency
C) Phase
D) Polarization
**Answer:** B
**Explanation:** Bandwidth is defined by the range of frequencies a signal occupies; the carrier’s
frequency sets its position in the spectrum.
**Question 2.** In Fourier analysis, the width of the main lobe of a rectangular pulse’s spectrum is
inversely proportional to:
A) Pulse amplitude
B) Pulse width
C) Sampling rate
D) Modulation index
**Answer:** B
**Explanation:** A narrower time‑domain pulse (smaller width) spreads its energy over a wider
frequency range (larger bandwidth).
**Question 3.** According to the Nyquist‑Shannon sampling theorem, the minimum sampling rate
required to perfectly reconstruct a signal with a maximum frequency of 5 kHz is:
A) 5 kHz
B) 7.5 kHz
C) 10 kHz
D) 15 kHz
**Answer:** C
**Explanation:** The sampling rate must be at least twice the highest frequency component
(2 × 5 kHz = 10 kHz).
**Question 4.** In a wireless link, the term “noise floor” refers to:
, Wisconsin WI Communication System Specialty
Exam
A) The maximum transmitted power allowed by regulation
B) The lowest detectable signal level due to thermal and environmental noise
C) The average received signal strength
D) The interference caused by adjacent channels
**Answer:** B
**Explanation:** The noise floor is the aggregate background noise level that limits the smallest usable
signal.
**Question 5.** Which modulation technique varies the instantaneous frequency of the carrier in
proportion to the message signal amplitude?
A) AM
B) FM
C) PM
D) QAM
**Answer:** B
**Explanation:** Frequency Modulation (FM) directly maps message amplitude to carrier frequency
deviation.
**Question 6.** Binary Phase Shift Keying (BPSK) provides which of the following advantages over
Amplitude Shift Keying (ASK) in a noisy environment?
A) Higher spectral efficiency
B Higher data rate
C) Better resistance to amplitude noise
D) Simpler demodulation circuitry
**Answer:** C
**Explanation:** BPSK encodes data in phase, making it immune to amplitude fluctuations that affect
ASK.
**Question 7.** In 16‑QAM, each symbol conveys how many bits?
A) 2
, Wisconsin WI Communication System Specialty
Exam
B) 4
C) 8
D) 16
**Answer:** B
**Explanation:** 16‑QAM has 16 distinct constellation points, representing log₂16 = 4 bits per symbol.
**Question 8.** Direct Sequence Spread Spectrum (DSSS) primarily improves resistance to:
A) Multipath fading
B) Co‑channel interference
C) Narrowband jamming
D) Path loss
**Answer:** C
**Explanation:** DSSS spreads the signal over a wide bandwidth, making narrowband interferers
ineffective.
**Question 9.** A convolutional encoder with constraint length 7 and rate 1/2 is best described as:
A) A block code that adds parity bits
B) A code that outputs two bits for every input bit, using 7 previous bits for memory
C) A Reed‑Solomon code for burst error correction
D) A turbo code with iterative decoding
**Answer:** B
**Explanation:** Rate 1/2 means two output bits per input bit; constraint length 7 indicates the
encoder uses the current bit plus six previous bits.
**Question 10.** The difference between theoretical data rate and actual throughput is most often
caused by:
A) Antenna gain
B) Propagation delay
C) Protocol overhead and retransmissions
, Wisconsin WI Communication System Specialty
Exam
D) Free‑space path loss
**Answer:** C
**Explanation:** Overhead (headers, acknowledgments) and error‑induced retransmissions reduce
usable throughput.
**Question 11.** In digital communications, a preamble is used for:
A) Power control
B) Channel coding
C) Frame synchronization
D) Frequency hopping
**Answer:** C
**Explanation:** The preamble provides a known pattern that receivers use to align to the start of a
frame.
**Question 12.** Which multiple‑access method assigns a unique code to each user to separate signals?
A) TDMA
B) FDMA
C) CDMA
D) OFDMA
**Answer:** C
**Explanation:** Code Division Multiple Access (CDMA) uses orthogonal spreading codes for user
separation.
**Question 13.** Orthogonal Frequency Division Multiplexing (OFDM) primarily combats which
impairment?
A) Co‑channel interference
B) Multipath delay spread
C) Adjacent‑channel interference
D) Thermal noise
Exam
**Question 1.** Which parameter directly determines the bandwidth of a sinusoidal RF carrier?
A) Amplitude
B) Frequency
C) Phase
D) Polarization
**Answer:** B
**Explanation:** Bandwidth is defined by the range of frequencies a signal occupies; the carrier’s
frequency sets its position in the spectrum.
**Question 2.** In Fourier analysis, the width of the main lobe of a rectangular pulse’s spectrum is
inversely proportional to:
A) Pulse amplitude
B) Pulse width
C) Sampling rate
D) Modulation index
**Answer:** B
**Explanation:** A narrower time‑domain pulse (smaller width) spreads its energy over a wider
frequency range (larger bandwidth).
**Question 3.** According to the Nyquist‑Shannon sampling theorem, the minimum sampling rate
required to perfectly reconstruct a signal with a maximum frequency of 5 kHz is:
A) 5 kHz
B) 7.5 kHz
C) 10 kHz
D) 15 kHz
**Answer:** C
**Explanation:** The sampling rate must be at least twice the highest frequency component
(2 × 5 kHz = 10 kHz).
**Question 4.** In a wireless link, the term “noise floor” refers to:
, Wisconsin WI Communication System Specialty
Exam
A) The maximum transmitted power allowed by regulation
B) The lowest detectable signal level due to thermal and environmental noise
C) The average received signal strength
D) The interference caused by adjacent channels
**Answer:** B
**Explanation:** The noise floor is the aggregate background noise level that limits the smallest usable
signal.
**Question 5.** Which modulation technique varies the instantaneous frequency of the carrier in
proportion to the message signal amplitude?
A) AM
B) FM
C) PM
D) QAM
**Answer:** B
**Explanation:** Frequency Modulation (FM) directly maps message amplitude to carrier frequency
deviation.
**Question 6.** Binary Phase Shift Keying (BPSK) provides which of the following advantages over
Amplitude Shift Keying (ASK) in a noisy environment?
A) Higher spectral efficiency
B Higher data rate
C) Better resistance to amplitude noise
D) Simpler demodulation circuitry
**Answer:** C
**Explanation:** BPSK encodes data in phase, making it immune to amplitude fluctuations that affect
ASK.
**Question 7.** In 16‑QAM, each symbol conveys how many bits?
A) 2
, Wisconsin WI Communication System Specialty
Exam
B) 4
C) 8
D) 16
**Answer:** B
**Explanation:** 16‑QAM has 16 distinct constellation points, representing log₂16 = 4 bits per symbol.
**Question 8.** Direct Sequence Spread Spectrum (DSSS) primarily improves resistance to:
A) Multipath fading
B) Co‑channel interference
C) Narrowband jamming
D) Path loss
**Answer:** C
**Explanation:** DSSS spreads the signal over a wide bandwidth, making narrowband interferers
ineffective.
**Question 9.** A convolutional encoder with constraint length 7 and rate 1/2 is best described as:
A) A block code that adds parity bits
B) A code that outputs two bits for every input bit, using 7 previous bits for memory
C) A Reed‑Solomon code for burst error correction
D) A turbo code with iterative decoding
**Answer:** B
**Explanation:** Rate 1/2 means two output bits per input bit; constraint length 7 indicates the
encoder uses the current bit plus six previous bits.
**Question 10.** The difference between theoretical data rate and actual throughput is most often
caused by:
A) Antenna gain
B) Propagation delay
C) Protocol overhead and retransmissions
, Wisconsin WI Communication System Specialty
Exam
D) Free‑space path loss
**Answer:** C
**Explanation:** Overhead (headers, acknowledgments) and error‑induced retransmissions reduce
usable throughput.
**Question 11.** In digital communications, a preamble is used for:
A) Power control
B) Channel coding
C) Frame synchronization
D) Frequency hopping
**Answer:** C
**Explanation:** The preamble provides a known pattern that receivers use to align to the start of a
frame.
**Question 12.** Which multiple‑access method assigns a unique code to each user to separate signals?
A) TDMA
B) FDMA
C) CDMA
D) OFDMA
**Answer:** C
**Explanation:** Code Division Multiple Access (CDMA) uses orthogonal spreading codes for user
separation.
**Question 13.** Orthogonal Frequency Division Multiplexing (OFDM) primarily combats which
impairment?
A) Co‑channel interference
B) Multipath delay spread
C) Adjacent‑channel interference
D) Thermal noise
