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Discriminator output

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 decoding, a connection from an earphone or speaker output is all that's required. This is because ACARS runs at a much lower speed, and the discriminator is not involved in AM reception.


Also see the Scandata faq q2 article for a list of older scanners' tap points. This is from an original article by the late Bill Cheek.


  • 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

Radio Shack

Other Radios

Why use a resistor and/or capacitor ?

See #6 through 8 of this URL: FAQ

Wikipedia Page showing Circuit and calculations for Discriminator Tap.


These pages or links contain more information on discriminator taps for many brands and models of scanners, including older models

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