VK3YE amateur radio pages

RF Actuated Keying Monitor


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Sending Morse on a rig without a sidetone is not impossible, but is not particularly pleasant either.

This battery-powered monitor has been designed to provide an audible indication of keying for those whose rigs lack a CW sidetone. Its sensor wire is wrapped around the transceiver's coax – no direct connection is required. Of course Morse isn't the only use for this nifty circuit – it should also be useful any time you need a simple alarm that detects the presence of RF.

RF collected at the sensor wire is rectified by a germanium diode. This produces a DC voltage that triggers a transistor switch. This then turns on a 555 audio oscillator that drives a speaker.

circuit of keying monitor