Finding the Audio

    In every scanner, one can find an RF receiver and demodulator chip which will have a pinout similar to the one in the side diagram. There are many types of these IC's found in scanners but they all share the same functional traits. They demodulate FM audio from an applied RF signal. The audio out pin 10, is the point from which the base band audio should be tapped. A nearby test point is a good choice. In order to find the correct pin however, one will either have to have the pinout diagram for the chip or probe for the pin using the tool described below.

Building an Audio Probe

The simple audio probe shown in the diagram is a simple and low cost tool that can be used to quickly and easily find the correct pin to tap. It is made from a mono ear phone that has had the mono plug cut off and then an alligator clip jumper has been cut in half and connected to the two remaining leads from the ear plug. A 0.1 microfarad capacitor is held with one clip and used as the probe. The other clip connects to a ground point within the circuit being probed.

Connect the ground clip to a shield on the circuit or the antenna ground and use the clip holding the capacitor as the probe tip. Power up the scanner and tune it to a digital station. The correct pin to be tapped will be the only one carrying audio.