[GreenKeys] How long can a local loop be?

[Jim Haynes]

Now most of what's in the Long Lines book is of course about long lines.
Where they might have used open wire or cable, perhaps composited 
circuits, perhaps carrier channels on a voice frequency circuit.
Composited means they used a set of low pass and high pass filters to
put voice and telegraphy over the same pair of wires.  Because a voice
grade pair is too valuable to use for telegraphy only.  But in a city
where a central office connects to TWX or other TTY subscribers in
the area they could afford to use a voice grade pair for telegraphy.
This could be DC telegraphy, or they might use one channel of a carrier
system and transmit audio tones on the pair.

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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