[GreenKeys] Telco Tones

[Randy and Sherry Guttery]

Larry Tighe wrote:
> I found the two filters/channel elements in the Model 28.
> 
> The tones 1070/1140 and 2260/2330 are 70 cycles apart thus the shift.  Being 
> an "RO", I suspect the higher tones are for answer back transmission.
> 
> Question:  Are tones on a line called "carrier"?  I originally thought the 
> carrier carries the AFSK, but it appears the AFSK is called "carrier".

The "classic" definition of carrier is that which transports 
a message (or such)... be it a mail carrier transporting an 
envelope or a (higher) frequency (albeit audio) carrying the 
binary "message" of a tty...

Which allows for a "stack" of carriers: such as the case of 
a transmitted carrier of RF energy - transporting an audio 
carrier of AFSK (sub-carrier) which itself is transporting 
the binary data for the tty: carrier -> sub-carrier -> 
intelligence (since the message could also be analog (sound) 
rather than digital- we'll call the "final" message 
intelligence).

Obviously, then - multiple sub-carriers can transport 
multiple (independent) messages...  which themselves might 
indeed be carriers as well (such as afsk being modulated 
with time-division multiplexed intelligence)...

Such is the case of high-speed modems - where even phase 
modulation gets "into the act"...  However - note even on 
these complex systems - just as with their much simpler 
300baud counter parts - they all have a "carrier detect" 
output to the host (and on most external modems - a carrier 
detect light)...

best regards...
-- 
randy guttery

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