[BC] question for you engineers

[Mark Durenberger]

To be more specific, the paths between telephone exchanges were 
almost always 4-wire (separate transmit path and receive path).  This 
was done so (one-way) amplifiers ("repeaters") could be used on the 
long hauls between exchanges.  The hybrids (4-wire to 2-wire 
converters) were used on the 'last mile' to/from the telephone instrument.

The use of the hybrid in the "ends" of the telephone system was a 
pragmatic solution to cut the last-mile wire costs in half.

If one could install a 4-wire (transmit-receive) path from radio 
station to telephone exchange, greater isolation could be obtained 
and the limiting factor for isolation would be the cross-talk at the 
caller's end.

Today we use "4-wire" end-to-end in our digital codecs, and isolation 
is nearly perfect.

Mark Durenberger, CPBE


----- Original Message ----- From: "Gary Glaenzer" <glaenzer at verizon.net>
Sent: Tuesday, January 01, 2008 11:16 AM


>"given that Ma Bell resisted the installation of any such devices 
>well into the '60's"
>
>not to nit-pick here, but EVERY 'long-line' repeater and EVERY 
>telephone from about the 40's onward contained a hybrid circuit