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Discriminator Output for Pro-35 Scanner
1998 The Fixer
This file originated at www.artofhacking.com.

Written by The Fixer, with a nod of thanks to Bill Cheek.

           Adding an AF Baseband Output to the Pro-35 Scanner

Do you own a Radio Shack Pro-35 Scanner?  Have you scoured the net for
weeks looking for mods for this radio?  Well, you've probably discovered
the hard way that there's no way to access forbidden bands or increase
the scanner's memory, but there is ONE mod which you can make which is
useful.  That is ading a baseband audio output to the radio, so that
programs such as POC32 will work.  The radio's audio amplifier does not
have the fidelity to pass digital signals properly, but by intercepting
the audio from the receiver before the amplifier, a much more accurate
signal is obtained.

This mod does not affect normal use of the scanner.  Do not attempt
unless you are already proficient at very fine conventional soldering,
as the points you are required to solder to are quite tiny.

First, open the scanner, remove the front keypad panel, and remove the
main board from the back case.

Next, locate IC401.  It's probably not labeled.  It's on the
daughterboard marked IF MODULE and it is the only 20-pin surface mounted
DIP on the board.  It will have a part number containing the number
10421 - with a prefix that varies, depending on the chip manufacturer du

Now, solder a lead of very fine insulated solid-core hookup wire to pin
11 of that IC.  Pin 11 is the baseband audio output.  You can risk
soldering a lead to this pin directly, or somewhat less risky is to
solder to the coupling capacitor off the pin.  Another trace from this
pin leads to a feedthrough just by the bottom center of the chip.  It is
that feedthrough to which I soldered the lead in my modification.

Next, install a jack on the case.  I used an RCA phono jack because it
offered the minimum depth into the cabinet, allowing for easy future
servicing, with the tradeoff that the jack is not flush.  A 1/8" or
1/16" headphone jack will also suffice. You will have to make cutouts in
both the case and the plated steel frame, and they must line up.

Connect the lead from Pin 11 of IC401 to the tip connector of the jack.
Connect the ring connector to a ground - it can be the frame, a solder
point on the ground bus of the circuit board, or the black line from the
rechargeable battery terminal.  If your jack is all-metal then simply
fastening it to the frame may provide a sufficient ground connection.

Finally, reassemble the radio and check it out - make sure all functions
still work, as the radio is not especially rugged when apart and
incidental damage can occur unknown to you at the time.

You now have a baseband audio output.  You can connect it directly to
the mic input of your sound card and use it with DSP decoding software
such as POC32, RTTY - fax - SSTV decoders - things that simply wouldn't
work if you got the signal from the earphone jack.  If you connect it to
an audio amplifier you will notice a remarkable improvement in the sound
fidelity over the scanner's own speaker.

Disclaimer: What you do with this mod is up to you.  I am not
responsible if you damage your scanner, nor am I responsible if you
violate someone's privacy with the aid of this mod.  Privacy laws such
as the American ECPA may restrict or prohibit the use of signal decoders
that would benefit from this mod - ask your national communications
authority before proceeding!

                                                (> The Fixer <)

(C) Copyright 1998 The Fixer

www.artofhacking.com - Who wants some!


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