Numerical - Calculation of frequency spectrum

Q.  An oscillator for an AM transmitter has a 100μH coil and a 10nF capacitor. If a modulating frequency of 10 KHz modulates the oscillator, find the frequency range of the side bands.
- Published on 13 Oct 15

a. 149 KHz to 169 KHz
b. 184 KHz to 296 KHz
c. 238 KHz to 296 KHz
d. 155 KHz to 166 KHz

ANSWER: 149 KHz to 169 KHz
 
Carrier frequency fc = 1/2Π√LC
= 1/ 2Π√100 * 10 - 6 * 10 * 10-9
= 1/2Π * 10-6
= 1.59 * 105 Hz
= 159 KHz
The modulating frequency fm is 10KHz
Therefore the range of AM spectrum is given by (fc fm ) to (fc + fm )
= (159 - 10) to (159 + 10)
= 149 KHz to 169 KHz

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