Date: 02-06-93 00:24 From: Bill Cheek To: All Subject: PRO-43 S-Meter! Greetings Scanner Fans! It had to happen! The fundamentals for an S-Meter exist alive and well in the PRO-43! Only a simple circuit and your choice of meter, analog or LED, is required for a jim-dandy S-Meter function! The key point in the circuit is the cathode of D-302 located on the bottom (solder side) of the AF Board (middle board). You will need the Service Manual for the PRO-43 to find it as it's not marked and it would take me 10,000 words to guide you to exactly where it is located. Call Tandy National Parts at (800) 442-2425 to order your manual: approx $10. Now here is the deal: Locate D-302 and either build the following circuit right there on the back of the AF board in the vicinity of D-302, or solder a wire to the cathode of D-302 and route it to somewhere else more convenient to feed the below circuit. This wire ought not to be very long, though, say not more than a couple of inches. Refer to the ASCII schematic diagram as follows: PRO-43 PRO-43 D-302 existing T-302 x---o--|<-------x PRO-43 ckt / | Connect | here | 0.01-uF 1N34A |------||------o-------->|----o---o-----------> (+) | | | | \ | To the | 47-k / | S-Meter of | ohms \ = 0.01-uF Your Choice | / | (This should | 1N34A | | be a jack |-----|<-------o---o----------> (-) mounted on ^ PRO-43 Ground^ the case of Legend: the scanner. | 1. ---||--- and = are 0.01-uF capacitors; disk, mylar, monolythic, chip | 2. --->|--- and ---|<---- are germanium diodes, 1N34A | is cathode < is anode 3. o means a connection, preferably soldered 4. The 47-k resistor is self-explanatory, I hope. 5. -------- and | are wires/conductors. | | 6. x is existing PRO-43 circuitry If you use an analog meter, preferably a real S-Meter like salvaged from an old junked CB rig, then rig it as follows to connect to the circuit above: 5-k Trim Pot (+) --------/\/\/\/\---o--------| | | | This should |-------| | be a plug of + some sort to The S-Meter connect to the Terminals mating jack on - the scanner | | (-)-----------------------------| You can also build the 10-segment LED S-Meter as shown in Volume 2 of my SCANNER MODIFICATION HANDBOOK, available from leading mail order radio dealers everywhere. ISBN 0-939780-14-3 published by CRB Research Books, Inc. Commack, NY. After connected and working, locate the PRO-43 very near a known strong transmitter, perhaps a ham transmitter, a police cruiser, your favorite security guard's handheld or right next to a cordless telephone, or anything else known to transmit a strong signal. Tune the scanner to the frequency, and adjust the 5-k trim pot above so the meter reads exactly full scale. All other signals will read proportionally lower to yield "relative signal strength" measurements! A hell of a circuit here, boys & girls! Have fun! Developed & distributed by: Bill Cheek COMMtronics Engineering PO Box 262478 San Diego, CA 92196-2478 Ok to distribute, but credit appreciated. Thanks! Bill Cheek --- GEcho 1.00/beta+ * Origin: Hertzian Intercept, San Diego (6pm-1pm) 619-578-9247 (1:202/731.1)