HAM HAM Radio Extra Class Test Modulation and Digital Signals Questions and Answers 2 — Questions and Answers
Question 1: What is the approximate bandwidth of a conventional FM phone signal on the HF bands?
- About 16 kHz (Correct answer)
- About 6 kHz
- About 30 kHz
- About 3 kHz
Correct answer: About 16 kHz
A conventional FM phone signal occupies approximately 16 kHz of bandwidth due to the deviation and modulation index used.
Question 2: Which digital mode uses orthogonal frequency-division multiplexing (OFDM) for amateur HF communication?
- WINMOR (Correct answer)
- PSK31
- RTTY
- CW
Correct answer: WINMOR
WINMOR uses OFDM techniques to provide robust digital communication over HF amateur radio channels.
Question 3: What is the function of a balanced modulator in a single sideband transmitter?
- It suppresses the carrier while producing upper and lower sidebands (Correct answer)
- It amplifies only the desired sideband
- It filters out audio frequencies above 3 kHz
- It generates the intermediate frequency
Correct answer: It suppresses the carrier while producing upper and lower sidebands
A balanced modulator combines the carrier and audio signals in a way that cancels the carrier, outputting only the two sidebands.
Question 4: What happens to the bandwidth of an FM signal if the deviation is held constant and the modulating frequency is doubled?
- The bandwidth increases (Correct answer)
- The bandwidth decreases
- The bandwidth stays the same
- The bandwidth is cut in half
Correct answer: The bandwidth increases
Increasing the modulating frequency while keeping deviation constant increases the occupied bandwidth per Carson's rule.
Question 5: In a PSK31 signal, what type of modulation shift represents a binary zero?
- A 180-degree phase shift (Correct answer)
- No phase shift
- A 90-degree phase shift
- A frequency shift of 31 Hz
Correct answer: A 180-degree phase shift
In BPSK31, a binary zero is represented by a 180-degree phase reversal of the carrier signal.
Question 6: What is the purpose of interleaving in digital communication modes used on amateur radio?
- To spread burst errors across multiple code blocks so error correction can recover the data (Correct answer)
- To increase the data transmission rate
- To reduce the power required for transmission
- To compress the signal bandwidth
Correct answer: To spread burst errors across multiple code blocks so error correction can recover the data
Interleaving distributes consecutive bits across different time slots so that burst errors affect only a few bits in each code block, making them correctable.
HAM HAM Radio Extra Class Test Modulation and Digital Signals Questions and Answers 2
What is the approximate bandwidth of a conventional FM phone signal on the HF bands?