![lm567 cw decoder lm567 cw decoder](https://www.elforum.info/uploads/monthly_03_2014/post-80311-139829773322.gif)
It draws only 100uA when the circuit is in its "off" or "rest" state. Here's how it works: U2 is a micro-power 5 Volt regulator. As shown, you can expect 6 months to a year of operation from an alkaline battery. S1, R5, C8 and Q1 form a time-delayed electronic switch for turning the circuit on and off, to conserve the 9 Volt battery. With the resistor and pot values shown, you can set the detector to any tone between 3 Hz. Just key (into a dummy load), allowing sidetone audio to be applied to the LM567 input, and adjust R3 to provide the brightest illumination of LED1.
LM567 CW DECODER SERIES
R3, in series with R2 and together with C4, sets the desired tone (i.e., the PLL reference), and should be set to the transceiver sidetone. These values are non-critical and can be varied +/- 50% with no noticeable difference in performance. Capacitors C1 and C2 set the PLL's bandwidth and loop filter characteristics. Audio from the speaker or headphone line is applied to the LM567's input pin through coupling capacitor C3. The circuit is a classic tone-detection application of the LM567 Tone Detector/PLL.
![lm567 cw decoder lm567 cw decoder](https://i.ytimg.com/vi/ESN0nFbv6eQ/maxresdefault.jpg)
(click on the picture to see larger version) VOILA!, You're zero-beat! Backing down on the receiver's audio gain reduces the detection bandwidth, giving your zero-beat more accuracy, but I've found you can easily get within 100 Hz with normal volume levels. While it's on, tune through the signal slowly, stopping when the LED lights it's brightest. This gives you about a minute to complete your tuning, at which time it shuts itself off, and conserves the 9 Volt battery. When you're ready to zero-beat the station calling CQ, press the pushbutton. Connect it in parallel with your speaker or headphones. Whether you're tone deaf, or just a geezer like myself, you might benefit with this handy little tuning aid. Usually, this is the same tone as your CW sidetone, 500-800 Hz, depending on your rig. Preparing to answer a CQ on CW, and with the RIT off, you slowly tune the received signal until it reaches the magic tone that means "zero-beat". You know the drill, typical on most transceivers. But at some point, I turned into a geezer ( Hey! not an OLD geezer!) and can't seem to find the right tone. I never used to have problems hearing zero-beat when tuning my transceiver. This project was constructed while that call was valid, and you may observe references to it. (click on any picture to see larger version) N5ESE's Zero-Beat Tuning Aid N5ESE's Zero-Beat Tuning Aid