Return path noise reducer

Details Return path noise reducer Return path noise reducer

1998-06-26

2004-03-23

Pascal, Robert (Department: 2817)

Wave transmission lines and networks

Transmission line inductive or radiation interference...

C336S229000, C361S118000

Reexamination Certificate

active

06710673

ABSTRACT:

BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates generally to an apparatus that reduces interference on a coaxial cable or hybrid fiber-coaxial cable system. Specifically, the invention relates to an apparatus that attenuates return path noise in a transmission system using coaxial cable wherein the noise is caused by external radio frequency (RF) signals or impulsive RF noise which are picked up and carried on to the coaxial shield by the system ground wire. Once on the coaxial shield, the RF signals traverse the coaxial shield and, at shielding deficiencies in the cable or other components and devices, the undesired signals transfer to the coaxial center conductor. The RF signals then travel along the return path of the coaxial center conductor to the coaxial network provider site and interfere with the signals sent from the subscriber to the provider.
The apparatus of the present invention comprises an RF signal choke that is formed by wrapping a solid conductor, such as 12-gauge copper wire, around a ferrite toroidal form. An alternative method of creating an RF choke is to place the requisite ferrite material around the conductor at one or more points along the conductor path. Throughout this specification and claims “RF Choke” is defined to include either embodiment. The apparatus is placed in series with the system ground wire and the ground electrode or ground source. The apparatus significantly attenuates undesired external RF signals that are picked up and transmitted to the system via the ground wire thereby preventing the undesired RF signals from reaching the coaxial shield. The apparatus is provided in a compact housing with a terminal coupler and a conductor so that it is easily connected between a coaxial network ground wire or ground block and a grounding electrode at a subscriber site.
2) Description of the Related Art
The cable television industry, as well as other telecommunications industries, use certain segments of the radio frequency (RF) spectrum for transmission of signals in the upstream and downstream paths of communication in two-way RF distribution networks. The RF distribution networks can constitute coaxial cable networks or hybrid fiber-coaxial cable-based RF transmission systems. The invention herein is described as if it were installed on a coaxial cable system, however, it should be understood that the present invention can be utilized in any RF distribution network which provides for two-way signaling and which is grounded or bonded in at least one location on the RF distribution network.
Coaxial networks are commonly used to provide cable television and other programming from a provider to multiple subscribers. Coaxial networks have expanded dramatically over the years and are being used for a variety of different functions. Recent developments in the industry include using bi-directional coaxial and bi-directional hybrid-fiber-coaxial (“HFC”) networks to transmit computer data via the Internet to television sets and computers. In addition, cable television providers are expanding into telephony and other communication services. In such networks there are occasions where information from a subscriber site must be transmitted back to the system provider via the node, hub or headend.
For example, various pay-per-view events distributed on cable television can be ordered by a subscriber by indicating acceptance of the pay-per-view event on the cable set top terminal at the subscriber site. The subscriber is instructed to input a response into the cable set top terminal or television set at the subscriber site and the response is transmitted along the center conductor of the coaxial cable from the subscriber site to the provider. The information is then received and used or acted upon by the provider. In addition to pay-per-view type events, the uses for coaxial networks have expanded to include communications and other areas which require a two-way path for the transmission of information along the center coaxial conductor of a coaxial network. When a signal is transmitted from a subscriber to a provider, this is known in the industry as communication via the “upstream path.”
The upstream path's frequency band typically ranges from 5 to 42 megahertz (MHz). This is known in the industry as the “upstream frequency band.” This frequency band corresponds to signals below the VHF television channel 2 in the United States NTSC system and therefore transmissions of signals on the upstream path do not interfere with the transmission of the primary signal along the downstream path (from the provider site to the subscriber sites).
One significant technical operational problem lies in the susceptibility of a coaxial network to RF interference from miscellaneous radiated or conducted ambient signals in the 5 MHz to 42 MHz band. These external signals can enter the coaxial network at one or more points and create interference or totally block the transmission of a return signal on the network. This effect is generally recognized and understood but is the source of significant concern to the industry. It is commonly referred to as “return path ingress” because miscellaneous interfering signals of the 5 MHz to 42 MHz frequencies tend to ingress into the network and interfere with “return” or “upstream” signals. One prior art device is the Coaxial Cable Shield Filter which is fully described in U.S. Pat. No. 5,091,707, to Wollmershauser, et al. the disclosure of which is incorporated herein by reference. The Coaxial Cable Shield Filter described in the '707 patent reduces interference caused by “off-air” RF signals that are conducted along the shielding of a coaxial cable. Such interference can cause problems with television reception at the subscriber sites if the conducted RF signals are allowed to enter a television or VCR tuner. The Coaxial Cable Shield Filter is designed to attenuate RF signals in a frequency range which interfere with signals traveling along the downstream path, namely, the primary signal sent from the provider site to the subscriber sites. The RF signals which the Coaxial Cable Shield Filter attenuates usually enter the coaxial network through direct pick-up (from a TV/VCR tuner) from external “off-air” RF signals (external sources) and are in the frequency tange corresponding to the frequencies used for downstream signals. When such RF signals are conducted along the shielding of the coaxial cable to the television or VCR tuner and are allowed to enter the tuner where they can mix with the downstream signals carried on the coaxial cable center conductor, they cause picture degradation and other problems in television reception.
The present invention is directed to solve a related problem but for which the coaxial cable shield filter is not suited, namely, interference which enters a coaxial network through its ground wire. Such interference is often caused by impulse noise caused by electrical devices within the subscriber site, as well as external RF signals from ham operators or other sources picked up by the wiring network at a subscriber site. Such interfering RF signals tend to cover a broad fluency range and encompass the frequency range of 5 MHz to 42 MHz.
Many household appliances use electrical contactors and similar electronic devices which produce impulsive noise. It is well known that as the current in an electromagnet rises and falls, its magnetic field grows and collapses. The moving field can induce a current in a nearby stationary conductor. Thus, when household appliances are operated, they can produce RF signals in electrical wing, metal casings of appliances, and metallic water pipes, etc. Such RF signals travel along the path of the conductor usually to a common ground source.
It is also known in the art that the electrical wiring in a typical home can act as an antenna and pick up RF signals in the air which are transmitted by remote sources such as ham radio operators, local television stations, etc. When the electromagnetic radiation comes into contact with the wiri

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