If you are operating your decoders in analog mode and are having interference trouble of running more then one at a time do the following. Connect two electrolytic capacitors across the output of the power pack in the following manner. Connect the positive lead of one capacitor to one of the power terminals. Connect the positive lead of the second capacitor to the other power pack terminal. Then connect the negative side of each capacitor together. Use capacitors with a minimum voltage rating of 20 volts. The capacitive rating of each capacitor should be in the range of 200 to 500 micro farads each. Be sure to insulate capacitor leads and connections with shrink tubing or electrical tap to avoid problems. You can find electrolytic capacitors at Radio Shack that will work.