Amateur Extra E8B: Modulation index and multiplexing
These are the 11 official questions in group E8B of the 2024–2028 Amateur Extra question pool, with the correct answer marked and a plain-English explanation of why it's right. The real exam asks one question from this group.
Learn E8B step by stepThe Amateur Extra course teaches this group in a short guided lesson, then drills you on the questions you miss. Start with the free lessons to see how it works.
- E8B01Question 1
What is the modulation index of an FM signal?
- AThe ratio of frequency deviation to modulating signal frequency Correct
- BThe ratio of modulating signal amplitude to frequency deviation
- CThe modulating signal frequency divided by the bandwidth of the transmitted signal
- DThe bandwidth of the transmitted signal divided by the modulating signal frequency
Why: Modulation index = frequency deviation ÷ modulating frequency.
- E8B02Question 2
How does the modulation index of a phase-modulated emission vary with RF carrier frequency?
- AIt increases as the RF carrier frequency increases
- BIt decreases as the RF carrier frequency increases
- CIt varies with the square root of the RF carrier frequency
- DIt does not depend on the RF carrier frequency Correct
Why: A PM signal's modulation index doesn't depend on the carrier frequency.
- E8B03Question 3
What is the modulation index of an FM phone signal having a maximum frequency deviation of 3000 Hz either side of the carrier frequency if the highest modulating frequency is 1000 Hz?
- A3 Correct
- B0.3
- C6
- D0.6
Why: 3,000 Hz ÷ 1,000 Hz = 3.
- E8B04Question 4
What is the modulation index of an FM phone signal having a maximum carrier deviation of plus or minus 6 kHz if the highest modulating frequency is 2 kHz?
- A0.3
- B3 Correct
- C0.6
- D6
Why: 6 kHz ÷ 2 kHz = 3.
- E8B05Question 5
What is the deviation ratio of an FM phone signal having a maximum frequency swing of plus or minus 5 kHz if the highest modulation frequency is 3 kHz?
- A6
- B0.167
- C0.6
- D1.67 Correct
Why: 5 kHz ÷ 3 kHz ≈ 1.67.
- E8B06Question 6
What is the deviation ratio of an FM phone signal having a maximum frequency swing of plus or minus 7.5 kHz if the highest modulation frequency is 3.5 kHz?
- A2.14 Correct
- B0.214
- C0.47
- D47
Why: 7.5 kHz ÷ 3.5 kHz ≈ 2.14.
- E8B07Question 7
Orthogonal frequency-division multiplexing (OFDM) is a technique used for which types of amateur communication?
- ADigital modes Correct
- BExtremely low-power contacts
- CEME
- DOFDM signals are not allowed on amateur bands
Why: OFDM is used for digital modes.
- E8B08Question 8
What describes orthogonal frequency-division multiplexing (OFDM)?
- AA frequency modulation technique that uses non-harmonically related frequencies
- BA bandwidth compression technique using Fourier transforms
- CA digital mode for narrow-band, slow-speed transmissions
- DA digital modulation technique using subcarriers at frequencies chosen to avoid intersymbol interference Correct
Why: OFDM uses subcarriers spaced to avoid intersymbol interference.
- E8B09Question 9
What is deviation ratio?
- AThe ratio of the audio modulating frequency to the center carrier frequency
- BThe ratio of the maximum carrier frequency deviation to the highest audio modulating frequency Correct
- CThe ratio of the carrier center frequency to the audio modulating frequency
- DThe ratio of the highest audio modulating frequency to the average audio modulating frequency
Why: Deviation ratio = maximum deviation ÷ highest audio frequency.
- E8B10Question 10
What is frequency division multiplexing (FDM)?
- AThe transmitted signal jumps from band to band at a predetermined rate
- BDividing the transmitted signal into separate frequency bands that each carry a different data stream Correct
- CThe transmitted signal is divided into packets of information
- DTwo or more information streams are merged into a digital combiner, which then pulse position modulates the transmitter
Why: FDM splits the signal into frequency bands, each carrying its own data stream.
- E8B11Question 11
What is digital time division multiplexing?
- ATwo or more data streams are assigned to discrete sub-carriers on an FM transmitter
- BTwo or more signals are arranged to share discrete time slots of a data transmission Correct
- CTwo or more data streams share the same channel by transmitting time of transmission as the sub-carrier
- DTwo or more signals are quadrature modulated to increase bandwidth efficiency
Why: TDM shares discrete time slots among signals.
Learn E8B step by stepThe Amateur Extra course teaches this group in a short guided lesson, then drills you on the questions you miss. Start with the free lessons to see how it works.