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An SSB signal is demodulated by using a synchronous demodulator. However, the locally arranged carrier has a phase error θ . Determine the effect of the error on demodulation. What will be the effect of this error if the input is DSB-SC in place of SSB?
For a DSB-SC input, the demodulated output suffers from amplitude attenuation proportional to cos(θ ), but experiences zero phase distortion.
For an SSB input, the phase error introduces a combination of the original message m(t) and its Hilbert transform 
, leading to severe waveform phase distortion.
If the phase error reaches exactly θ =±90, a complete loss of the demodulated signal power occurs for both DSB-SC and SSB inputs.
For a DSB-SC input, when the phase error is exactly θ =±90, the system experiences the Quadrature Null Effect (QNE).
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