[RTTY] trying to understand afsk

[wb6rse1 at mac.com]

I use cocoaModem AFSK on a Mac in USB mainly because I've become very  
accustomed to USB CW tones, operating CW for many years. IE "up" DX  
splits are higher tones when searching for "the spot." I set  
cocoaModem to USB RX and TX and the rig is set to USB.

I use a Mark of 1415 Hz and a shift of 170 Hz. This also centers the  
signal in my 500 Hz CW filter, which often is quite useful.

But the tone pair is actually arbitrary in cocoaModem because the  
frequencies change depending where you tune to by clicking in the  
waterfall display.

That said, if I see a spot I want to print, I subtract 1.5 KHz from  
the spot when I tune the rig. If the spot was correct, the signal will  
fall in place centered on 1500 Hz. If I am posting a spot, I simply  
add 1.5 KHz to the USB frequency on the rig.

However, If I move the tone pair by clicking away from 1500 Hz in the  
waterfall, that new "center" frequency is what must be added. So if  
the rig is tuned to 14080 and the station I want to spot is centered  
on 800 Hz, the correct frequency for me to spot is 14080.8. If 2200  
Hz, I'd spot 14082.2.

If operating LSB, all above is simply reversed.

This is all much easier done than said.

73 - Steve WB6RSE