Re: LF: RE: something for the weekend ??

[DL4YHF@aol.com]

Think I got it...

The output from the upper mixer branch is:
  sin(a+b) - sin(a-b)  

The assumption "delayed this by 90 degrees" should give
  cos(a+b) - cos(a-b) 
does not look right in my opinion.


Instead, do the "90° phase shift" from the upper mixer's output in the term where all trigonometric functions have only a single argument. 
Upper mixer branch
sin(a+b)-sin(a-b) = 2*cos(a)*sin(b)  [ go figure ...]
Now only one argument in each trig function, looks safe to do the 90 degree phase shift by adding 90 degrees in the argumens:
Upper mixer branch, delayed by 90°:
2*cos(a+90°)*sin(b+90°) = - 2*sin(a)*cos(b) = - sin(a-b) - sin(a+b)

So this is the delayed output from the upper mixer branch. Now add upper and lower branch (without the phase shifters):
Lower branch : sin(a+b)-sin(a-b)
Upper branch : -sin(a+b)-sin(a+b)
Add both:    sin(a+b)-sin(a-b)-sin(a-b)-sin(a+b) = -2sin(a-b)
Et volia, the upper sideband has been cancelled (should have subtracted for USB ;)


Hope this is not totally wrong..

Regards,
 Wolf DL4YHF.