From The RadioReference Wiki
The Discriminator output from a scanner is the raw, unfiltered signal that a scanner produces before it is sent to the audio stage for output through the speaker -- also called the "baseband audio." This discriminator source is required for applications such as Trunker, T4Win, UniTrunker, and DSD. Most scanners must have a simple modification made to them to feed the discriminator output to Data Slicers, or in the case of UniTrunker, a soundcard.
Note that for providing a signal for ACARS or MPT-1327 decoding, a connection from an earphone or speaker output is all that's required. This is because these modes run at a much lower speed, and the discriminator is not involved in AM reception (for ACARS decoding).
Also see the Scandata faq q2 article for a list of older scanners' tap points. This is from an original article written by the original scanner hacker and guru the late Bill Cheek.
- BC-245 Discriminator Tap
- JPEGs of BC246 discrim tap
- BC296D/UBC 3300XLT
- BC350A Discriminator Tap
- BC350C Discriminator Tap
- BC-396T Discriminator Tap
- NOTE: You must be a member of the BCD396T Yahoo to view this message.
- The JPEG for the discriminator tap can be viewed here
- BC-780 Discriminator Tap
- BC785D Discriminator Tap
- BC796D Discriminator Tap
- BC895XLT Discriminator Tap
- BCD996 Discriminator tap point
- BCT15 Discriminator tap point
- NOTE: Look dead center of the circuit board, then go right and down. Both the 996 and BCT15 appear to share the same tap point location.
- Pro-26 Discriminator Tap
- Pro-93 Discriminator Tap
- Pro-95 Discriminator Tap
- Pro-96 Discriminator Tap
- Pro 97 Discriminator Tap
- Pro-106 Discriminator Tap
- Pro-164 Discriminator Tap
- Pro-2052 Discriminator Tap
- Pro-2053 Discriminator Tap
- Pro-2066 Discriminator Tap
Why use a resistor and/or capacitor ?
See #6 through 8 of this URL: Discriminator.nl FAQ
These pages or links contain more information on discriminator taps for many brands and models of scanners, including older models