ModulationRadio Telephony — DGCA CPL practice questions
Question 1 of 16
In amplitude modulation, what is varied?
All 16 questions — Modulation
Radio Telephony · DGCA CPL. The correct option is marked on each.
Q1. In amplitude modulation, what is varied?
- A.The amplitude of the carrier✓
- B.The frequency of the carrier
- C.The speed of light
- D.The antenna length
Why: AM varies the carrier's amplitude in step with the audio; frequency stays fixed.
Q2. One reason a voice cannot be transmitted directly is that it would require:
- A.Too little power
- B.An impractically long antenna (its wavelength is enormous)✓
- C.A satellite
- D.Frequency modulation
Why: n impractically long antenna (its wavelength is enormous). Audio wavelengths are hundreds of km; modulating a high-frequency carrier allows a short antenna and frequency sharing.
Q3. The information in an AM signal is carried in the:
- A.Carrier
- B.Sidebands✓
- C.Antenna
- D.Local oscillator
Why: The carrier carries no information; the sidebands do.
Q4. If the highest audio frequency is 3 kHz, the AM bandwidth is:
- A.3 kHz
- B.6 kHz✓
- C.1.5 kHz
- D.9 kHz
Why: AM bandwidth = 2 × highest audio frequency = 2 × 3 = 6 kHz.
Q5. Modulating beyond 100% depth causes:
- A.A clearer signal
- B.More range
- C.Distortion and interference to adjacent channels✓
- D.Lower frequency
Why: istortion and interference to adjacent channels. Over-modulation distorts the audio and splatters into neighbouring channels.
Q6. At 100% AM modulation, the proportion of power in the carrier is about:
- A.33%
- B.67%✓
- C.100%
- D.0%
Why: About two-thirds of the power is in the carrier, which carries no information.
Q7. In FM, what is held constant?
- A.Frequency
- B.Amplitude✓
- C.Wavelength of the audio
- D.Bandwidth
Why: mplitude. FM varies frequency while amplitude stays constant — hence its noise immunity.
Q8. FM is generally NOT used for VHF aviation voice because of its:
- A.Low cost
- B.Capture effect (weaker signal silenced)✓
- C.Wide range
- D.Use of sidebands
Why: apture effect (weaker signal silenced). FM's capture effect would silently suppress a second transmitting aircraft — unsafe.
Q9. Aviation VHF voice uses AM mainly because:
- A.It is cheaper
- B.Two simultaneous transmissions produce an audible heterodyne, alerting users✓
- C.It has the longest range
- D.It needs no antenna
Why: AM reveals when two stations transmit together (a squeal); FM's capture effect would silently lose one.
Q10. SSB is preferred for HF because it is:
- A.Simpler to receive
- B.More power- and bandwidth-efficient✓
- C.Immune to all fading
- D.Higher frequency
Why: SSB suppresses the carrier and one sideband, concentrating power and halving bandwidth.
Q11. SSB uses how much bandwidth compared with full AM?
- A.Twice
- B.Half✓
- C.The same
- D.Four times
Why: Transmitting one sideband instead of two halves the bandwidth.
Q12. The emission designator for aviation VHF voice (AM telephony) is:
- A.J3E
- B.A3E✓
- C.F3E
- D.A1A
Why: 3E. A3E = AM double-sideband telephony (VHF voice); J3E = SSB telephony (HF voice).
Q13. The aviation receiver architecture that converts every signal to a fixed intermediate frequency is the:
- A.Direct-conversion receiver
- B.Superheterodyne receiver✓
- C.Crystal set
- D.Regenerative receiver
Why: The superheterodyne mixes the signal down to a fixed IF for easy selectivity and gain.
Q14. In the transmitter chain, the stage that generates the carrier is the:
- A.Modulator
- B.Oscillator✓
- C.Power amplifier
- D.Antenna
Why: The oscillator generates the carrier; the modulator then mixes the audio onto it.
Q15. Modulation depth m is defined as:
- A.Carrier voltage ÷ audio voltage
- B.Audio (modulating) voltage ÷ carrier voltage✓
- C.Frequency ÷ wavelength
- D.Power ÷ bandwidth
Why: udio (modulating) voltage ÷ carrier voltage. m = Vm/Vc, usually expressed as a percentage.
Q16. Compared with AM, FM generally requires:
- A.Less bandwidth
- B.More bandwidth✓
- C.No bandwidth
- D.The same bandwidth
Why: By Carson's rule, FM bandwidth ≈ 2(deviation + fmax), usually more than AM.