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scratchytcarrier

Tapping your PRO-97 made easier

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Based on a post from a certain popular scanner mods site, without the author's or site's permission. This is all public knowledge anyways. Have phun.

FM discriminator tap access
Radio type: Rat Shack (GRE) PRO-97

1. Prepare a 1/8" or 3/32" stereo headphone jack or an RCA jack by soldering a piece of wire (signal) to a 10K ohm 1/4 watt (brown-black-orange-gold) resistor. Solder the resistor to the "tip" terminal of the jack (as shown in the picture below). The article's original author used a Radio Shack part number 274-249 1/8" jack here and used blue and black wires for the signal and ground lines respectively. I (scratchytcarrier) used a RCA jack which provides a little more leeway with placement inside the radio housing. Solder another piege of wire (ground) to the "sleeve" terminal of the jack as shown above. After soldering, wrap all the terminals with electrical tape or pot them in epoxy or silicone sealer. Attach a small crimp fitting to the end of the signal wire if you don't feel comfortable soldering to the inside of your radio.
3849_pro-97_discriminator-2.jpg

2. Remove the battery cover and battery holder.

3. Remove the four screws and lift the back cover off of the scanner.

4. Locate "TP4", which is a small wire pin. This is connected to pin 9 of the 3361 chip (this is the discriminator output). It's shown in the picture below with the blue wire attached. CAREFULLY solder a wire to TP4 or crimp it on if you can get a small enough pressure fitting like I did.
3849_pro-97_discriminator-1.jpg

5. Now you'll need a place to connect the ground wire. I tinned the end of my ground wire and slipped it under a prong on one of the metal shields. Easy peasy.

6. Next, run the two wires through a hole in the chassis. The author ran his through the lower right screw hole. For a more permanent connection, you could drill a hole through the plastic case to mount the phone jack.

7. Replace the battery pack and the battery cover.

8. Secure the chassis with 3 screws (or all 4 if you drilled a new hole).

9. The original writeup specifies using the belt clip to hold the stereo jack as shown in the photo below:
3849_pro-97_discriminator-3.jpg
This is not only ugly and unprofessional but also negates usage of the belt clip, so forget true portable operation if you do it this way. I drilled a hole in the housing just a little bit southeast of the PC/IF jack when the radio is stood upright (shown near the bottom left in this photograph) and mounted mine there. This positions it just above the 24-pin header shown in the middle picture.

10. You're done. Plug one end of a 1/8" stereo cable, with an appropriate adapter if necessary, into the jack and the other end to the line or microphone input of that old dedicated XP box in the corner's sound blaster. Now go find a nice hot packet/DMR/P25 frequency, fire up your decoder software and go nutz. If you've only used the headphone jack for monitoring before then you will immediately notice the increase in performance, since you're getting nice undistorted, wideband audio straight off the demodulator IC (in other words, without the audio preamp, filtering, AGC and all that crap getting in the way. Yuck). You will also be able to use a data slicer if you have one (cough cough L0PHT cough cough).

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