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Old radios often had a ‘Magic Eye’ tuning indicator, normally green, that responded to the tuning, it was a nice visual way to tune in a signal. Many modern radios are fitted with a CW centre tune indicator, often like on my FTDX-1200 its very small and hard to see. This little circuit can be connected into the audio out circuit, (just connect to the Data out of the radio/across extension speaker) or if it’s a kit /homebrew rig just put it across the outer pins of the volume control, its fairly high impendence input and should have little effect on the circuit it connected to.
The module will accept a wide range of input voltages from just a few mV up to 3 V of audio.
The Magic Eye Indicator uses a Phase Locked Loop chip to detect when a preset tone is being received. The tone is selectable by the builder to match the sidetone of the receiver, a 25 turn perscision trimer is fitted to allow accurate frequency selection. The unit is tuneable between 500 and 900Hz. The bandwidth is approx. 30Hz
The unit is very flexible as regards its input signal levels, a few mV up to 3V can be used so it is fine either put it in a homebrew radio (across the volume control) or fitted into a external speaker case. the unit canbe powered from 6 to 15V DC.
Heres an idea, when the indicator activates it's second output can be used to activate another side tone device (oscillator). The idea is despite having a wide filter or a lot of noise on the band a clean CW tone can be heard that follows the incoming Morse, the fact that the PLL is tight means you end up with a tight CW filter without any noise or ringing at all, just the oscillator of your choice. This does work but of course its not really intended to be used this way and high-speed CW can cause problems as can weak signals with a lot of noise. I am not listing this as an official feature but If you like playing then give it a try. There is a special output on the PCB for this.
Magic Eye CW Tune indicator
Full Kit Instructions can be downloaded here (Use these to make your own if you wish
For USA select DX postage please