# Frequency Modulation Help

• MYMLA
In summary, the exercise involves frequency modulation of a pure tone carrier signal of 440 Hz with another sine wave of 440 Hz and an amplitude of 1760. The deviation and index of modulation can be calculated as 1760 and 4 respectively. The frequency of the carrier and sideband partials can be found by adding and subtracting the modulating frequency (440 Hz) from the carrier frequency (440 Hz), resulting in sidebands at 880 Hz, 0 Hz, 1320 Hz, -440 Hz, 1760 Hz, -880 Hz, 2200 Hz, and -1320 Hz. The amplitudes of these sidebands can be determined using Bessel functions, taking into account the effects

## Homework Statement

[/B]
A pure tone (sine) carrier signal of 440 Hz is frequency modulated by another sine wave of frequency 440Hz with an amplitude of 1760.
(a) For the steady-state portion of the output signal generated by synthesis above, calculate: i) the deviation and ii) the Index of modulation.

(b) For the steady-state portion of the output signal generated by synthesis above, calculate the frequency of the carrier and sideband partials.

(c) For the steady-state portion of the output signal generated by synthesis above, and using the Bessel functions represented below, calculate relative amplitude of the carrier and sideband partials, allowing for aliasing.

MYMLA said:
A pure tone (sine) carrier signal of 440 Hz is frequency modulated by another sine wave of frequency 440Hz with an amplitude of 1760
Hello Mymla,

Please read the guidelines; we aren't supposed/allowed to help if no effort is made by the poster.

In the mean time: check the numbers: modulating 440 Hz with 440 Hz ? 1760 whatkindathings ?

## Homework Statement

A pure tone (sine) carrier signal of 440 Hz is frequency modulated by another sine wave with a frequency of also 440Hz. The amplitude of the modulating wave (The deviation) is 1760. The amplitude of the carrier is 1.
(a) For the steady-state portion of the output signal generated by synthesis above, calculate: i) the deviation and ii) the Index of modulation.

(b) For the steady-state portion of the output signal generated by synthesis above, calculate the frequency of the carrier and sideband partials.

(c) For the steady-state portion of the output signal generated by synthesis above, and using the Bessel functions represented below, calculate relative amplitude of the carrier and sideband partials, allowing for aliasing.

## The Attempt at a Solution

The deviation is 1760 as this is the amplitude of the modulator
The index of modulation is the deviation/mod frequency = 1760/440 = 4

Side bands = 440+fm, 440-fm, 440+2fm, 440-2fm, 440+3fm, 440-3fm……. As far as the deviation. (1760 above and below 440)
So:
First pair: 440+440 and 440-440
Second Pair: 440+880 and 440-880
Third pair: 440+1320 and 440-1320
Forth pair: 440+1760 and 440-1760
So we have side bands at: 880, 0, 1320, -440, 1760, -880, 2200, -1320

This is where I get stuck. How do I work out the amplitudes of these. How does aliasing effect them?