Coherent Detector and DSB-SC Signal

A coherent detector is a type of demodulator used in communication systems to extract the original message signal from a modulated signal. It works by multiplying the received signal with a local oscillator signal that is synchronized with the carrier frequency of the modulated signal. This multiplication process allows the coherent detector to recover the original message signal.

DSB-SC (Double Sideband Suppressed Carrier) is a type of modulation where the carrier signal is suppressed, and only the two sidebands containing the information are transmitted. In DSB-SC modulation, the original message signal is multiplied by a carrier signal to produce the modulated signal.

Noise at the Detector Output

In a communication system, noise is an unwanted signal that corrupts the received signal. It can be introduced by various sources such as thermal noise, interferences, and distortions. When the DSB-SC signal is received at the coherent detector, it may contain noise along with the original message signal.

The coherent detector works by multiplying the received signal with a local oscillator signal. This multiplication process is sensitive to the phase of the received signal and the local oscillator signal. When the received signal and the local oscillator signal are perfectly in phase, the coherent detector can accurately recover the original message signal.

However, when there is noise present in the received signal, it affects the phase of the signal. The noise adds random fluctuations to the phase of the received signal, which in turn affects the phase of the local oscillator signal. As a result, the multiplication process at the coherent detector output will be affected.

Answer: Option A

The in-phase component refers to the component of the received signal that is in phase with the local oscillator signal. In the presence of noise, the in-phase component will be affected by the random fluctuations in the phase introduced by the noise. Hence, the noise at the detector output is the in-phase component.

Conclusion

In a coherent detector, the noise at the detector output is the in-phase component. This is because the noise affects the phase of the received signal, which in turn affects the phase of the local oscillator signal during the multiplication process. Understanding the behavior of noise in a coherent detector is crucial for designing robust communication systems that can accurately recover the original message signal in the presence of noise.