Spurious Signal Criteria for Voiceband Telephone Equipment

A customer's telephone terminal equipment is usually connected to the serving central office by a pair of wires. This pair of wires, referred to as a loop, is normally a part of a multipair cable containing 6 to 2700 pairs. Most of these pairs will be used for voice frequency service for other customers. However, pairs within this cable can be used for services such as data and broadcast program channels or systems such as subscriber loop carrier used to serve multiple customers. These other services and systems are not restricted to voiceband frequencies but can cover a frequency range from dc to several megahertz. Pairs within a common cable sheath are in very close proximity to each other and, as a result, a small portion of the electromagnetic field, set up by the customer's communication signal, can couple into other pairs. Cable design and manufacturing techniques are used to minimize this coupling but cannot eliminate it. This coupled signal can interfere 809 with other signals in the cable if its level is not controlled. To control this interference, requirements are placed on the maximum allowed signal levels and administrative rules, referred to as spectrum management,1 are used. Because of the large number of voiceband terminals, specialized administrative processes are not used for them. Such use would lead to inefficient use of cable facilities and would be economically burdensome. The interference caused by voiceband systems is controlled by requirements on the maximum allowed signed levels.