Subelement G: Transmitters— Topic 53: Oscillators & Modulators
Question 3-53G3
Element 3 (GROL)What is the total bandwidth of a FM phone transmission having a 5 kHz deviation and a 3 kHz modulating frequency?
Explanation
The total bandwidth of an FM phone transmission is determined by Carson's Rule, which estimates the approximate bandwidth needed to transmit an FM signal. Carson's Rule states that the bandwidth (BW) is equal to two times the sum of the maximum frequency deviation ($\Delta$f) and the maximum modulating frequency (f$_m$).
Using the given values:
Maximum frequency deviation ($\Delta$f) = 5 kHz
Maximum modulating frequency (f$_m$) = 3 kHz
Applying Carson's Rule:
BW = 2 * ($\Delta$f + f$_m$)
BW = 2 * (5 kHz + 3 kHz)
BW = 2 * (8 kHz)
BW = 16 kHz
Therefore, the total bandwidth is 16 kHz. Options A, B, and C are incorrect as they do not apply Carson's Rule correctly; 3 kHz is the modulating frequency, 5 kHz is the deviation, and 8 kHz is only half of the calculated bandwidth.
Related Questions
3-53G1 What is the modulation index in an FM phone signal having a maximum frequency deviation of 3,000 Hz on either side of the carrier frequency when the modulating frequency is 1,000 Hz?3-53G2 What is the modulation index of a FM phone transmitter producing a maximum carrier deviation of 6 kHz when modulated with a 2 kHz modulating frequency?3-53G4 How does the modulation index of a phase-modulated emission vary with RF carrier frequency?3-53G5 How can a single-sideband phone signal be generated?3-53G6 What is a balanced modulator?