MOTM

Tkacs, Ken schrieb:
> 
> If you feed a sine into both inputs of a ring modulator, 
> you get a sine an 
> octave higher, not a rectified sine. It outputs the sum 
> and difference 
> signals, so the sum of "1" and "1" is "2 (doubled 
> frequency)," and the 
> difference is zero. 

> I'm not sure where you're getting the rectification from. 

Very true. However, "zero" means "zero Hz" (and not "zero voltage").
That is, the difference frequency becomes a DC voltage!
(DC = "AC @ 0Hz" with amplitude = DC voltage). This
adds to the double frequency sine wave, so you get a sine
of 2f that is *raised* above 0V - and here's where the similarity
to "rectification" comes in.

With the old formula (from memory - I hope it's right, and it's
easier with cosinus to write down):

cos(x) * cos(x) = 1/2 + 1/2 * cos(2x) >= 0.

JH.