|Provide dual performance suppression to effectively minimize
interference in voice frequency loops
Radio Frequency Interference
(RFI) occurs when a
source of RF emission is located in very close proximity to the cable plant or where
adequate shielding and bonding of the telephone facilities is not feasible, such as near
or at the customer premises.
Generally, this unwanted RF energy is
caused by an AM broadcast band radio station. The RF energy is picked up by the cable
plant, which acts as an antenna. The unwanted signals are demodulated to voice frequency
and carried directly to the telephone set.
Metallic noise enters the network on one side of the pair with the return
path provided by the other side of the pair. Longitudinal noise enters the network on
either one or both sides of the pair; ground is the return path. Both metallic and
longitudinal RF interference are attenuated by these UL listed networks.
Audible RF noise may also be created within
the telephone set. Circuits and certain components within a telephone set can act as both
antenna and receiver (demodulator) for RF emissions from a nearby source. Maximum
performance of any RFI suppression network can not be assured in such situations.