> are really 600 ohms resistive worldwide, and that the complex reference > impedance specified was chosen to approximate the impedance presented by > the combination of the network equipment and the real-world loop? (With the > intent that equipment designed to provide a complex source impedance would > perform better than equipment designed for 600 ohms)
The complex reference impednace indeed represents the combination of network equipment and real-loop. However, there were no Machiavellian schemes involved. The Telecom Network was never designed, it just evolved. As one old mentor used to say, you can bugger it a bit here and a bit there and it will be very forgiving. However, you cannot bugger it in all places, all of the time. Network design objectives were not the same everywhere. Some people actually went for good quality, other believed that transmission over barbed wire in the prairies was quite acceptable, them ranchers didn't want quality, they wanted cheap. Therefore, the ideal complex impednace is different depending on what the objectives were at one time. Ciao, Vic
