[GreenKeys] FSK shifts

[Duncan Brown]

I was surprised to learn that KPH is running 170Hz shift on RTTY and 
that is now the standard for commercial RTTY/SITOR/NAVTEX.

850Hz shift was the standard shift for a long time and gives some 
diversity assistance in TUs that can copy with just one tone. Hams using 
850 Hz shift got some flack from CW operators because of their "wide" 
signal among the narrow CW signals.  That, plus the (once) crowded CW 
bands, forced the change to amateur RTTY switching to 170 Hz. (More 
stable TX & RX made narrower shifts more practical, but didn't require it.)

Other than narrower transmitter bandwidth, is there any advantage to 170 
Hz shift over 850 Hz? When & why did the commercials change to 170 Hz?  
With assigned channels, they would not have the QRM problems that we 
have on the Ham bands.

Thanks,

Duncan
K2OEQ