AET Communication Systems — Questions and Answers
Question 1: What frequency band does aviation VHF communication primarily use?
- 118–137 MHz (Correct answer)
- 88–108 MHz
- 406–512 MHz
- 960–1215 MHz
Correct answer: 118–137 MHz
Aviation VHF communications operate in the 118.000–136.975 MHz frequency band for air-to-ground and air-to-air voice communications.
Question 2: What modulation type is used by VHF aviation voice communication radios?
- FM
- AM (Correct answer)
- SSB
- DSB
Correct answer: AM
VHF aviation communications use Amplitude Modulation (AM) because it allows simultaneous reception from multiple stations and simulates 'breaking squelch' when multiple transmitters key at once.
Question 3: What is the channel spacing used by modern 8.33 kHz VHF aviation radios in Europe?
- 25 kHz
- 8.33 kHz (Correct answer)
- 50 kHz
- 100 kHz
Correct answer: 8.33 kHz
Europe mandates 8.33 kHz channel spacing to increase frequency spectrum capacity in congested airspace.
Question 4: Which component in a VHF comm transceiver ensures the carrier frequency is stable?
- Mixer
- Frequency synthesizer with PLL (Correct answer)
- IF amplifier
- Squelch circuit
Correct answer: Frequency synthesizer with PLL
A frequency synthesizer using a Phase-Locked Loop (PLL) generates precise, stable carrier frequencies across all selectable channels.
Question 5: What is the purpose of a squelch circuit in an aviation receiver?
- Amplify weak signals
- Mute the receiver when no signal is present (Correct answer)
- Filter harmonics
- Reduce transmitter power
Correct answer: Mute the receiver when no signal is present
The squelch circuit silences the audio output when received signal strength falls below a set threshold, eliminating background noise between transmissions.
Question 6: What does SELCAL stand for in aircraft communication systems?
- Selective Calling System (Correct answer)
- Self-Calibrating Amplifier Loop
- Sequential Electronic Link Call
- Satellite Electronic Communication Link
Correct answer: Selective Calling System
SELCAL (Selective Calling System) allows ground stations to alert a specific aircraft over HF/VHF without requiring continuous radio monitoring by the crew.
AET Communication Systems
What frequency band does aviation VHF communication primarily use?