Sunday, February 14, 2016

LM567 tone decoder, build and adjust frequency.

..Well the idea is to start preparing the Arduino RTTY decoder to replace the Yaesu YR-901 internals (just in case I fail to fix it).

I will need to decode(1) the mark and space from the RTTY signal and also the CW tone so that signals can then be recovered and displayed.

The LM567 it's a nice available chip to do it and there are plenty of designs around, I just selected one, tweaked (some values I got from datasheet and are not the original from the schematic) and built:
My assembly does not include the 20K pull up (on PIN 8) resistor at the moment, it will be on final design after removing the LED. Not on the schematic but built is an audio 600:600 isolation transformer between the radio output and the capacitor connected to LM567 input (PIN 3). My IC is not an LM567 but a DBL567 equivalent (Daewoo seminconductor, the brand as the cars!....) .

Then connected to the FT-707 headphone output and tested against live signals:

..worked first time.

For checking the lock frequency the best method is connecting a frequency counter to PIN 5 (PLL VCO) and count the frequency there (without input signals). I used the scope for the task!
Here's the range on mine using the 10K multi-turn adjustable resistor.

....need to increase the cap to go to the CW 600Hz tone.


And set for the moment:

That's it...have a nice week!

(1) - Technically it's note decoding since there is no encoding process, it will be more demodulating, since a carrier will be modulated by a signal, either mark, space or on off for CW.

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