Coherent signal source, incoherent noise source, Im thrown!

[amlangford]

I am thrown by a reference in literiture Im reading that suggests that a 6dB difference exists between a "coherent" signal source and an "incoherent" noise source.

I think the term coherence used here is referring to in time i.e. a coherent signal source will have strong correlation at periodic time intervals, whereas a true noise source is always uncorrelated and thus incoherent.

Is my understanding of the (in)cohorent term correct and any explanation of the 6dB difference???

Thank you

 

[jallem]

coherent refers to synchronism to the local oscillator.
If the LO is free running then is incoherent and if
the LO is running out of the signal itself by extracting
the carrier then is coherent.
Noise is always said to be incoherent since phase and
frequency varies randomly.

 

[bulx]

Re: Coherent signal source, incoherent noise source, Im thro

It is usual to make the assumtpion that noise is uncorrleated (ie; autocorrlation of the noise in an impulse function), and not unsual to make the asumption that signal is also of the same nature. These assumtpions make a lot of calculations and approximations possible, whatever be the reality.

But these say nothing about the signal power. The nature of the randomness of the signal or noise doesnt lead to any conclusion on power relations. So there is something else in the context that leads to the 6 dB.
-b

hmm..but may be if we compare a equipower correlated and uncorrelated signal signal, the PSD at a certain frequency, the uncorrelated would have flat psd, whereas the correlated wouldnt be flat, some relation could exist..