Add On S-Meter driver for Hamtronics® R series receivers

To provide an s-meter output proportional to signal input on receivers that use the Motorla MC-3357 or MC-3359 style if amp/limiter/detector. The circuit could also be used on other receivers by connecting the circuit input to the receivers last IF stage.

The circuit described here deals with providing a dc voltage from near zero to just over 5 volts dc depending on signal input to allow a controller or local meter to be driven. This circuit will drive the ACC controllers s-meter input directly. A calibration pot is provided to allow the user to set the s-meter calibration as desired.

Construction can be simple breadboard wiring as the whole circuit will fit on Radio Shacks 1 7/8" by 2 7/8" breadboard. The ic should be mounted in a socket to allow easy replacement. Use a 7808 voltage regulator or a local 8-9 vdc if available to power the circuit. The circuit does not load the receiver in any way and will not degrade the receivers performance. Try to keep the lead from the if amp/limiter/detector mixer output as short as possible. The detector diodes can be 1N914 or 1N60.

Circuit designed by Kevin K Custer W3KKC

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