Radio Shack Pro 97 Discriminator Tap Mod

-UPDATE- Pictures now online! See Brett’s site here -UPDATE-
This radio is closely fasioned to the Pro 95 in respect to chip placement and audio processing. The following is an excerpt from the Yahoo Pro-97 group discussion – Thanks to Brett for the great info!

The discriminator output on the Pro-97 comes from pin 9 of the MC3361
chip. Fortunately, RS made a very handy solder point connected to this
pin and labeled it "TP4".

Most of the references that I have seen recommend that you use attach
a 10K ohm resistor to the output from TP4. Then you connect the other
end of the resistor to the center conductor in the audio cable. For
the outer conductor (cable shield) you just connect it to a convenient



I’ll try to get pictures and step by step instructions better formatted in the coming days. As Brett said, this modification CAN CAUSE INREPAIRABLE DAMAGE and should only be done at your own risk.

By performing this modification, you will be able to pull baseband (raw) audio from the scanner prior to any audio processing. Using the following programs below, you can monitor the workings of a trunked radio system.

Unitrunker – Use straight audio from the discriminator output of your radio to the sound card of a computer. Tracks Motorola Type I and II, Project 25 9600 bps, EDACS (both 4800 and 9600 bps), and MPT1327 systems without the use of a data slicer.

Trunker – Monitors Motorola systems by using the audio from the discriminator tap of a radio, fed through a data slicer then in to the serial port of a computer.

You can read more about data slicers if you choose to go the Trunker route on RadioReference’s Wiki on Data Slicers.

Other general specs on the Pro 97 Triple Trunker Scanner:
• 1000 channels

• Triple-trunking

• Alpha-numeric display for ID tagging allows frequencies to be easily identified by the name you assign to them

• Lighted keypad for use in low light

• Signal Stalker II

• Skywarn

• AM/FM mode selector

• 20dB attenuator

• Digital weather alert indicates watch, warning, statement or test statement along with seven preprogrammed NOAA WX stations

• Five service search keys for marine, fire/police, air, CB and Ham bands

• One priority channel

• PC interface, cloning

• Key lock for safety

• Key tone on/off

• Low battery indication

• Frequency lock-out

• Power save

• EEPROM memory backup

• Three power options: 4 “AA” batteries (not included), 150mA rechargeable batteries (not included), 9V AC/DC power adapter (not included)

• Can use AC adapter #273-1767/C and DC adapter #273-1863/C

• Two battery cases—one for alkaline and the other for rechargeable batteries

• Rotary volume control with switch and rotary squelch control

• Jacks: earphone, PC interface/cloning and external power

• BNC antenna connector

• Includes belt clip, 6″ flexible rubber antenna and two battery cases

• Triple conversion Superheterodyne receiver virtually eliminates image-type interference

• Frequency Coverage: 25-54, 108-136.9875, 137-174, 216.0025-221.9975, 222-225, 225.025-405.975, 406-512, 806-960 (excluding cellular) and 1240-1300MHz

• Scanner includes: detachable flexible antenna, belt clip, two battery holders

• Size: (less antenna) 6-1/2×2-5/8×1-3/4″

• Includes: VHF Lo/Hi, UHF, VHF-Air, 800MHz, Dual-Trunking, Extended Coverage

Many thanks to, Brett from the Group, Mods.DK, Brett Casebolt and an unnamed source that helped confirm TP4 is actually connected to the CPU.