One input to a conventional AM modulator is a 500 KHz carrier with an amplitude of $20V_P$. The second input is a 10 KHz modulating signal that is of sufficient amplitude to cause a change in the output wave of $±7.5V_P$. Determine - 1. Upper and lower side frequencies - 2. Modulation coefficient and percent modulation - 3. Peak amplitude of the modulated carrier and upper and lower side frequency voltages - 4. Expression for the modulated wave. - 5. Draw the output spectrum -

Mumbai University > Computer Engineering > Sem 3 > Electronic Circuits and Communication Fundamentals

Marks: 10 Marks

Year: Dec 2013

1.The upper and lower side frequencies are simply the sum and difference frequencies, respectively:

$$f_{usf}=500kHz + 10 kHz = 510 kHz \\ f_{lsf}= 500 kHz - 10 kHz = 490 kHz$$

2.The modulation coefficient is determined from equation below

$$m=\dfrac{7.5}{20}=0.375$$

Percent modulation is determined from equation below

$$M=100 \times 0.375=37.5 …