[RTTY] Pseudo FSK Again

[Jim W7RY]

Well I was not able to get David's Pseudo FSK circuit working the way I thought it should. 

You were correct David, I did not have the 2 volts of bias on pins 2 and 10. But when I did hook the bias up, I could not get stereo to work (right and left separate channels). I believe this is because the inputs share a common point which is the 2 volt bias line. I was not able to get the circuit to work at all without adding a transformer to the inputs. I used 1K to 8 ohm transformers with 8 ohm winding going to the sound card and the 1K winding going to the board.---

So I got to thinking.. I had already tried to use a simple opto isolator being driven by the sound card. That kinda worked but not enough voltage to get the opto isolator to fully conduct....

So..... I used the same transformer as above, and used that to drive a Darlington opto isolator, 4n33. 

That works perfectly! Nice clean FSK and it starts to work with the level at about 30 (on a scale of 1-99). But when I turn the output of the sound card all the way up, the opto isolator is saturated, (emitter voltage at .72 volts). Keys the FSK line on the Icom IC7600 and IC7410 just fine. Again, 8 ohm side of the transformer to the sound card, and the 1K winding directly to the diode in the opto-isolator.

Easy, simple and cheap! 

Thanks for all the great ideas David. 

Oh.... I downloaded a neat little tool called tone generator.exe. Generates any tones you want... Even generates two tones at once. Very helpful in troubleshooting and engineering the new circuit. 

I know... The fact that stereo doesn't work is not that big of a deal because only one transmitter is on at the same time, but if I were to do multi instead of SO2R, it would be a big deal.

73 and Merry Christmas!

Jim W7RY