GROL Modulation and Signal Types 2 — Questions and Answers
Question 1: An AM carrier has a peak amplitude of 100V and is modulated at 80%. What is the peak amplitude of each individual sideband?
- 40V (Correct answer)
- 80V
- 160V
- 20V
Correct answer: 40V
Each sideband amplitude equals (m/2) × carrier amplitude = (0.8/2) × 100 = 40V.
Question 2: An AM transmitter produces 1000W of carrier power. What is the total output power at 100% modulation?
- 2000W
- 1500W (Correct answer)
- 1250W
- 3000W
Correct answer: 1500W
Total AM power = Pc(1 + m²/2) = 1000(1 + 0.5) = 1500W at 100% modulation.
Question 3: What is the RF bandwidth of an AM signal with an audio frequency range of 300Hz to 5kHz?
- 5kHz
- 4.7kHz
- 10kHz (Correct answer)
- 9.4kHz
Correct answer: 10kHz
AM bandwidth = 2 × highest audio frequency = 2 × 5000Hz = 10kHz.
Question 4: What occurs when an AM signal is overmodulated (modulation index exceeds 1.0)?
- The signal automatically converts to FM
- The carrier is cut off during negative peaks, causing distortion and adjacent-channel splatter (Correct answer)
- Bandwidth is reduced by half
- Power efficiency improves significantly
Correct answer: The carrier is cut off during negative peaks, causing distortion and adjacent-channel splatter
Overmodulation clips the carrier on negative audio peaks, producing flat-topping that generates harmonics and causes splatter interference on adjacent channels.
Question 5: An AM transmitter operates on 1600kHz and is modulated by a 4kHz audio tone. Where are the two sidebands located?
- 1592kHz and 1608kHz
- 1596kHz and 1604kHz (Correct answer)
- 1598kHz and 1602kHz
- 1590kHz and 1610kHz
Correct answer: 1596kHz and 1604kHz
The upper sideband is at 1600 + 4 = 1604kHz and the lower sideband is at 1600 − 4 = 1596kHz.
Question 6: What percentage of total AM transmitter power is contained in both sidebands combined at 100% modulation?
- 50%
- 25%
- 33.3% (Correct answer)
- 66.7%
Correct answer: 33.3%
Sideband power = Pc × m²/2 = 500W; total power = 1500W; 500/1500 = 33.3%.
Question 7: Which ITU emission designator identifies a standard double-sideband full-carrier AM voice transmission?
- F3E
- J3E
- A3E (Correct answer)
- R3E
Correct answer: A3E
A3E designates double-sideband full-carrier amplitude modulation used for analog voice telephony.
GROL Modulation and Signal Types 2
An AM carrier has a peak amplitude of 100V and is modulated at 80%.
What is the peak amplitude of each individual sideband?