[GreenKeys] ITTY 850 shift?

[Jim Haynes]

Originally the frequencies for 850 Hz shift were 2125 mark and 2975 space. 
But when we got good SSB gear it often turned out that 2975 was too high 
to be passed by the radio bandwidth.  So other frequency pairs were 
chosen, such as 2125 and 1275.  (Trying to keep one of the 850 shift 
frequencies the same so you only had to make one new detector filter 
instead of two.)  Operating radio it doesn't matter a lot which 
frequencies are chosen because you can tune the radio receiver to place
the signals wherever your filters are.  But with military radios that
allowed only integral 1 KHz or 0.1 KHz channel frequencies there is
some restriction in which frequencies can be chosen.  And with audio
frequencies over the Internet you can't tune the receiver, so unless
there are agreed-upon tone frequencies you have to use one of the late
FSK converters like Dovetron that allow choosing the tone frequencies.

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 	"Ya can argue all ya wanna, but it's dif'rent than it was."
 	"No it ain't! No it ain't!  But ya gotta know the territory."
 		Meredith Willson, The Music Man