I have an idea which should work as an easy to build tune indicator. I have used an LM567 tone decoder (8 pin DIP) which costs $2.22 from Mouser electronics. The Mouser data sheet shows possible circuits. I use it to drive my telegraph sounders from off the air CW signals. I set mine up for about an 80 Hz BW and for 600 Hz signals. The drive level is not too critical and it seems relatively immune to weak adjacent signals. It will take a handful of parts, but should work just fine for your purpose. You could even build two of them and have one peaked on say 580 Hz and one on say 620 Hz and both would flash if you tune to 600 Hz. Even a 3 light display if you like lights a red one for just too low, a green one for right on freq. and a blue one for tuned just a bit to high. I use a potentiometer to set the center frequency, although you could replace this with a fixed resistor when you get it right. The LM586 can drive (or sink ?) up to 15 ma, so should be fine direct
ly driving a 5 ma or less LED. If questions you can reply off list to my ARRL or QRZ e mail. I posted this since others may also have a use for these ideas. Rick KL7CW
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