--- In [email protected], "John H. Fisher" <[EMAIL PROTECTED]> wrote: > > The speed of dark is your friend. I can't help but think there is a way > to take advantage of the delay when a signal goes down a coax to > generate the first derivative or rate of change of a signal. Suppose you > put your signal into an op amp non-inverting input. And you run that > same signal through 3 ft of coax to the inverting input of that op amp. > The inputs are 3 nanoseconds apart. The output of the op amp is the > instantaneous first derivative. By sampling this at a fixed rate we have > the first derivative of the desired signal. Essentially this is what the > quadrature sampling does. There must be a way to take advantage of this > coax delay to demodulate signals :-) > > -- > Regards,
> John > > ========================================================= > email: [EMAIL PROTECTED] > photos: http://www.flickr.com/photos/k5jhf/sets/ > videos: http://www.youtube.com/profile?user=k5jhf > files: http://briefcase.yahoo.com/[EMAIL PROTECTED] > web page: http://www.geocities.com/[EMAIL PROTECTED] > call sign: K5JHF > ========================================================= > Hi John, Just a quick off-the-cuff reply... I think you need to consider that delay and true quadrature signals are not the same. When you delay, you delay for a single frequency, not the modulation "sidebands" if-you-will. A true quadrature implementation results in same phase shift for all frequencies of interest. A passive device example is a quadrature power divider. Passive quadrature power dividers are always bandwidth-limited. Your reference to first-derivative reminds me of Group-Delay. Hmmm... Be a bit more specific about what you're proposing... 73's David
