What is the bandwidth of main lobe in the spectrum of BPSK signal with carrier frequency = 1 MHz and bit rate = 1 kbps ?

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  1. 1 kHz
  2. 2 kHz
  3. 3 kHz
  4. 4 kHz

Answer (Detailed Solution Below)

Option 2 : 2 kHz
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Explanation:

Bandwidth of the Main Lobe in BPSK Signal Spectrum:

Definition: In Binary Phase Shift Keying (BPSK), the spectrum of the modulated signal consists of a main lobe and side lobes. The bandwidth of the main lobe is a critical parameter that determines the frequency range over which most of the signal's power is concentrated. This bandwidth is influenced by the bit rate of the signal.

Formula for Bandwidth: The bandwidth of the main lobe for the spectrum of a BPSK signal can be approximated using the following relation:

Bandwidth of the main lobe = 2 × Bit Rate

Here:

  • Bit Rate: The rate at which bits are transmitted, typically measured in bits per second (bps).
  • 2: A factor that accounts for the symmetric nature of the main lobe around the carrier frequency.

Given Data:

  • Carrier Frequency = 1 MHz (This value does not affect the bandwidth of the main lobe.)
  • Bit Rate = 1 kbps = 1000 bps

Calculation:

The bandwidth of the main lobe is calculated as:

Bandwidth of the main lobe = 2 × Bit Rate

Bandwidth of the main lobe = 2 × 1000 bps

Bandwidth of the main lobe = 2000 Hz =  2 kHz

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