Numerical - Calculation of frequency spectrum
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.
a.) 149 KHz to 169 KHz
b.) 184 KHz to 296 KHz
c.) 238 KHz to 296 KHz
d.) 155 KHz to 166 KHz
Correct Answer: a.) 149 KHz to 169 KHz
Explanation:
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
