[time-nuts] simple explanation of noise spectra with mixing, etc.

[Jim Lux]

Is there a handy "one pager" kind of explanation of noise spectra after 
some forms of signal processing..

For instance, if you have a oscillator which has a 1/f characteristic, 
and you mix it with itself, what is the spectra of the output of the mixer.


Or if you have a 1/f^3 characteristic (e.g. from a crystal oscillator, 
very close in) or a 1/f^2 (from a VCO).

Specifically, I've got some folks working with homodyne radars (where 
you demodulate the received signal with a sample of the transmitted 
signal, but sometimes with an offset mixed in, etc.) and I'm looking for 
a quick intro to this kind of thing at a sort of 
empirical/phenomenological as opposed to analytical..

"If you see X on a spectrum analyzer or FFT, it is because of Y"...

Similarly, they're building PLLs and know about the 20log10(N) thing, 
but what should the shape of things underneath be.