For a binary phase-shift keying modulator with a carrier frequency of 70 MHz and input bit rate of 10 Mbps, the maximum Upper Side Frequency (USF) and minimum Lower Side Frequency (LSF) are respectively

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  1. 85 MHz and 65 MHz
  2. 75 MHz and 65 MHz
  3. 55 MHz and 45 MHz
  4. 75 MHz and 45 MHz

Answer (Detailed Solution Below)

Option 2 : 75 MHz and 65 MHz
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Detailed Solution

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Concept:

The spectrum of BPSK is represented as:

F3 S.B Madhu 09.06.20 D 3

Max upper side frequency \(\left( {USBF} \right) = {f_c} + \frac{{{R_b}}}{2}\)

Minimum lower side freq. \(\left( {LSBF} \right) = {f_c} - \frac{{{R_b}}}{2}\)

Where,

fc = carrier frequency

Rb = Input but rate

Calculation:

Given:

Rb = 10 Mbps, fc = 70 MHz

Max upper side frequency will be:

\({f_c} + \frac{{{R_b}}}{2} = 70 + \frac{{10}}{2} = 75\;MHz\)

Min lower side frequency will be:

\({f_c} - \frac{{{R_b}}}{2} = 70 - \frac{{10}}{2} = 65\;MHz\)

Hence, the BPSK spectrum  will be:

F3 S.B Madhu 09.06.20 D 4

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