Learning session- PAM

Learning how AM works to try understand it, I won't build any actual circuits but like learning the principles. So the 555 is creating a 40kHz carrier signal for the 500Hz voice signal that you would talk into or hook a microphone up to. It becomes a modulated signal through the NPN and then sent through a band pass filter to filter out switching harmonics? The final signal is a amplitude modulated signal? I'm sure others would like to know so I figured I'd ask the questions. Also I've seen some add a DC voltage to the voice signal, why is that done and is it necessary ? And lastly, how do you size the emitter resistors for best signal. I kinda just sized them to whatever made it look best by eye. I'm an electrical engineer but I don't deal with modulation at all and just wanted to understand, it's been years.

published 9 years ago