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Q3:  How do I connect to the Discriminator Output?


If you need the raw NFM Discriminator baseband audio signal
for external purposes, the best way to access it is via a
jack installed in a convenient, unobtrusive location on the
scanner. Use Figure 1 as a general guide.

1A  BASE SCANNERS: Install an RCA or other jack in a desired
    place on the scanner's external case, typically the rear

1B  HANDHELD SCANNERS: If you can find the space, use a
    standard monaural 1/8" phone jack or a 3/32" mini phone
    jack.  Some scanners are so cramped inside that even
    these won't fit. In that case a strip of 3 pinline
    sockets can be melted into the plastic case and wires
    soldered to the inside protrusions.

    The middle pinline socket is not connected to anything;
    it's just there as strength and support for the pinline
    plug you make, with the shield ground soldered to one
    end and the audio- center soldered to the other end:

    GND---o o o---NFM DSCR (audio)

    "Break-apart" pinline plugs/sockets are available from
    Mouser, DigiKey, and Hosfelt.

    Digi-Key:  p/n A208-ND          (800) 344-4539
    Hosfelt:   p/n 21-274           (800) 524-6464
    Mouser:    p/n 151-5520/5530    (800) 346-6873

    These little puppies are good for a lot of hacker needs,
    so get a supply!

2.  Connect the shell or outer frame part of the jack to
    scanner chassis ground.  (Use one end socket for pinline

3.  Connect the (+) leg of a 10-uF tantalum capacitor (Radio
    Shack #272-1436) to the Discriminator output Pin. (Capacitor
    should be tantalum, but can vary in value from 2.2-uF to
    10-uF at a voltage rating of 16-35 vdc.)

4.  Connect the center conductor of a shielded coax (RG-174,
    etc) or shielded mic cable to the (-) leg of the
    capacitor. NOTE: if the distance from the NFM tap to the
    jack is less than 3", then a single unshielded hookup
    wire will do fine.

5.  Connect the shield of the cable at this end to a nearby
    PCB ground trace or spot.

6.  Connect the center conductor of the other end of this
    cable (or single hookup wire) to the center or hot lug
    of the jack.

7.  Connect the shield of the cable at that end to the
    ground lug of the jack.

8.  Fabricate or buy a shielded patch cable with one end to
    mate with the new jack on the rear of the scanner at
    that end....and the other end to mate with whatever jack
    is on the tape recorder, processor, decoder, or whatever
    device is to be connected at the other end.

Now you are ready to connect a data decoder interface to the
baseband audio output jack. See Figure 1 above.

Figure 1 can be found at Q2.

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