Telephonic communications – Transmission line conditioning – Interference suppression
Patent
1994-05-23
2000-06-20
Weaver, Scott L.
Telephonic communications
Transmission line conditioning
Interference suppression
333 12, H04M 174
Patent
active
060786620
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a Radio Frequency Interference (RFI) filter for a telecommunications device, and more particularly to an RFI filter for telephone equipment that suppresses frequencies in the range from about 450 kHz to about 150 MHz.
BACKGROUND OF THE INVENTION
Electromagnetic interference in the so-called radio frequency range is commonly referred to as Radio Frequency Interference (RFI). RFI can occur in a telecommunications network whose wiring is subject to strong radio frequency electrical fields. RFI is a problem in telecommunications because it impairs reception of the signal transmitted through the telecommunications network. Impairment of a transmitted signal is particularly undesirable in the transmission of voice frequency signals because of the need for a telephone subscriber to receive clear, accurate voice communications.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a means for suppressing RFI in voice frequency loops of telecommunication circuitry.
It is a further object of the invention to provide such suppression of RFI in the range of 450 kHz to 150 MHz.
According to the invention, each of a pair of inductors has a lead connectable respectively to tip and ring leads of the telephone circuitry. The second lead of each inductor is connected to a respective coil of a transformer. To complete the tip and ring series circuits, the free lead of each coil of the transformer is connectable to respective tip and ring leads. The pair of inductors form a first stage of filtering while the transformer provides a second stage of filtering. In an alternative embodiment, each of a pair of inductors has a lead connectable respectively to tip and ring leads of the telephone circuitry. The second lead of each inductor is connected to a ferrite-core inductor. To complete the tip and ring series circuits, the free lead of each ferrite-core inductor is connectable to respective tip and ring leads. The pair of inductors form a first stage of filtering while the ferrite-core inductors provide the second stage of filtering. Each device provides suppression of RFI from 450 kHz to 150 MHz. A fuse may precede each inductor to protect the device from power surges and the like.
Other aspects, objects, features, and advantages of the present invention will become apparent to those skilled in the art upon reading the detailed description of preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of an RFI filter in accordance with a preferred embodiment the invention.
FIG. 2 is a schematic diagram of an RFI filter in accordance with a second preferred embodiment of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the present invention, the invention will now be described with reference to the following description of an embodiment taken in conjunction with the accompanying drawing. Referring to FIG. 1, there is shown a schematic diagram of an RFI filter 10 in accordance with a preferred embodiment of the invention. The filter 10 has a first stage 20 for suppressing lower frequencies of RFI and a second stage 22 for suppressing higher frequencies of RFI. The filter 10 is insertable in series in the tip T and ring R conductors of telephone circuitry. A first inductor L1 and a second inductor L2 form the first suppression stage 20. The first inductor L1 is connectable in the tip T branch of circuitry while the second inductor L2 is connectable in the ring R branch of circuitry. In the second suppression stage 22, a transformer is connected in series in the tip T and ring R circuitry. A first winding W1 of the transformer T1 is connected in series in the tip T branch of circuitry, following the first inductor L1. The second winding W2 of the transformer T1 is connected in series in the ring R branch of circuitry, following the second ind
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