The Uniden Bearcat 145XL is a vintage 16 channel scanner. There is ample space to equip it with a discriminator output.

The receiver IC is an MC3359. The unfiltered audio can be found on pin 10. It's quite strong, which could damage a computer's soundcard. Therefore, an attenuation of about 50% is created by a two resistor voltage divider.

BC145XL

Pin 10 of the MC3359 contains the unfiltered audio

The components at pin 10

Follow the next steps to make the discriminator output:

• Install a 3.5 mm mono socket in the scanner's back
• Solder a 10 k resistor to pin 10 of the receiver IC
• Connect another 10 k resistor to the other lead of the resistor connected to pin 10
• Solder the other lead of the second resistor to the metal shield of the IF coil.
• Connect the junction of both resistors with the signal solder lug of the chassis socket (red wire)
• Connect the chassis socket's ground lug with the metal shield of the IF coil (black wire)

Chassis socket in the scanner's back