Much of the noise that occurs in intercom systems arises from the coupling of DC and AC signals. The elimination of the noise, while retaining the primary signal, is the goal of communication specialists. They use bypass capacitors to filter out the AC noise component of the intercom. A simple intercom circuit uses an operational amplifier and transistor to generate a signal large enough for the intercom. A capacitor placed at the noninverting input of the operational amplifier removes any noise component coupled with the signal before amplification. The filtering of the input to eliminate the noise component cleans up the transmission quality of the signal.
