Question

If l is coherance length and cis the velocity of light the coherant time is

Answer 1

Coherence length. In physics, coherence length is the propagation distance over which a coherent wave (e.g. an electromagnetic wave) maintains a specified degree of coherence. Wave interference is strong when the paths taken by all of the interfering waves differ by less than the coherence length.

Answer 2

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In coherent detection the local carrier generated at the receiver is phase locked with. the carrier at the transmitter. Hence it is also called synchronous detection. In non coherent detection the local carrier generated at the receiver not be phase. Locked with the carrier at the transmitter.