Question

The frequency response curve (Figure) for the filter circuit used for production of AM wave should be ______.

(i)	(ii)
(iii)	(iv)

1. (i) followed by (ii).
2. (ii) followed by (i).
3. (iii).
4. (iv).

Options

• a, b and c

• b, d and c

• c and d

• b and a

Answer 1

a, b and c

Explanation:

(i) Sideband frequencies: The AM wave contains three frequencies f_c, (f_c + f_m) and (f_c – f_m), f_c is called carrier frequency, (f_c + f_m) and (f_c – f_m) are called sideband frequencies.

(f_c + f_m) – Upper sideband (USB) frequency

(f_c – f_m): Lower sideband (LSB) frequency

Sideband frequencies are generally close to the carrier frequency,

(ii) Bandwidth: The two sidebands lie on either side of the carrier frequency at equal frequency interval ω_m.

So, bandwidth = {(ω_c + ω_m) – (ω_c – ω_m)} = 2ω_m 

To produce an amplitude modulated wave, bandwidth is given by the difference between the upper sideband frequency and the lower sideband frequency. Bandwidth = ω_USB – ω_LSB = (ω_c + ω_m) – (ω_c – ω_m)