Posted on Feb 2, 2013    10220

This design is for an external signal strength meter that is analog, digital, and audible for mobile transmitter hunters. The S meter also incorporates a gain circuit. The digital LED bar graph display has a very fast response time. The 3.3-KO resistor near LM3914 can be replaced with a 5-K pot to control LED brightness. The S2A position gives a 2:1 gain and the S2B position gives about a 50:1 gain. The calibration pots control the amount of meter action relative to the gain.

Smeter - schematic

The optional dampening circuit is used for the averaging of a transmitted signal that has modulated power or when a dip on the voice peaks occur. The capacitors can be switched one by one or switched into a very slow response using 5.8 I"F total capacitance.

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