Interactive video distribution systems – Video distribution system with upstream communication – Remote testing of cable system
Reexamination Certificate
1997-07-29
2001-09-18
Faile, Andrew (Department: 2611)
Interactive video distribution systems
Video distribution system with upstream communication
Remote testing of cable system
C725S125000, C348S192000, C324S525000, C324S512000
Reexamination Certificate
active
06292944
ABSTRACT:
This invention relates to methods and apparatus for isolating a point of ingress of noise into communication circuits. It is disclosed in the context of CATV systems which include provision for both the transmission of cable channels downstream from the head end to subscribers and the return of commands and the like upstream from subscribers to the head end. Much of the noise introduced into such systems is introduced by the relatively poorer quality circuits including the wiring internal to the subscribers' homes and up to the CATV taps. Consequently, isolating a particular subscriber's circuit in some way and measuring the resulting ingress can provide an indication whether ingress is attributable to that subscriber's circuit.
Because the CATV system return amplifiers which amplify the signal returning from the circuit to the head end effectively isolate more upstream customers from the measurement, the method and apparatus of the present invention heavily load the return path between an adjacent pair of such amplifiers and measure the effect of such loading on the signal in the return path between the adjacent amplifiers. If the return path is heavily loaded, on the order of 15 dB or so, between an adjacent pair of such amplifiers in the return path bandwidth of ~5 MHz-~42 MHz, and ingress noise disappears from the return path between the adjacent amplifiers, that is an indication that the ingress noise source is further downstream away from the head end. If this process is conducted beginning at the head end and moving away from the head end, the ingress noise source can be accurately isolated between, for example, two return path amplifiers. Then, other techniques can be employed to isolate the particular source of the noise ingress, for example, inadequate shielding or a bad connection in a subscriber's circuit connected in the return path between those two amplifiers, and repair it.
The mechanism by which the loading is achieved is a lowpass filter having a cutoff frequency just above the typically ~5 MHz-~42 MHz return path frequency band. If the CATV system technician starts at the head end and works his or her way outwardly along the system from the head end, performing this process at each return amplifier, the ingress noise will continue to disappear from the signal returning to the headend until the technician reaches the amplifier immediately downstream from the section of the return path to which the noise source subscriber's circuit is connected. Then the technician will have isolated the noise source to one or at most a relatively few subscribers whose subscriber circuits can then be tested for noise ingress and repaired as necessary.
According to one aspect of the invention, a method is provided for detecting the source of a signal in a CATV circuit. The CATV circuit comprises a plurality of amplifiers, each having a first, or input port and a second, or output port. Nodes of the CATV circuit couple the second ports of respective amplifiers to the first ports of next adjacent amplifiers in the circuit. The method comprises the steps of proceeding along the circuit from node to node, determining at each node whether the signal is present, reaching a node at which the signal is not present, and determining that the signal source is in the node tested immediately preceding the node at which the signal is not present.
According to this aspect of the invention, the step of determining at each node whether the signal is present comprises the steps of providing a first filter having a passband including the signal frequencies, connecting the first filter to the node, and determining the effect on the signal of coupling the first filter to the node.
Further according to this aspect of the invention, the step of providing a filter having a passband including the signal frequencies includes the step of providing on the filter a third port for coupling to an instrument for measuring signal strength. The step of determining at each node whether the signal is present further comprising coupling the instrument to the third port and measuring the strength of the signal at the third port.
Additionally according to this aspect of the invention, the step of providing a first filter having a passband including the signal frequencies comprises the step of providing a first filter having a passband including the signal frequencies and a first characteristic impedance in the passband. The step of determining at each node whether the signal is present further comprises the step of providing a second filter having a passband including the signal frequencies and a second characteristic impedance in the passband, coupling the second filter to the node, and determining the effect on the signal of coupling the second filter to the node.
Additionally according to this aspect of the invention, the step of coupling the first filter to the node and the step of coupling the second filter to the node together comprise the steps of alternately coupling the first and second filters to the node.
Further according to this aspect of the invention, the second filter is coupled to the third port. The step of determining at each node whether the signal is present further comprises the step of comparing the strength of the signal with the first filter coupled to the node and the strength of the signal with the second filter coupled to the node.
According to another aspect of the invention, apparatus for detecting the source of a signal in a CATV circuit comprises a first filter having a passband including the signal frequencies, at least a first conductor for coupling the first filter to the node, and an instrument for determining the effect on the signal of coupling the first filter to the node.
According to this aspect of the invention, the first filter comprises a third port and the instrument comprises a signal strength meter. The apparatus further comprises at least a second conductor for coupling the signal strength meter to the third port.
Additionally according to this aspect of the invention, the first filter further comprises a first filter having a first characteristic impedance in the passband. The apparatus further comprises a second filter having a passband including the signal frequencies and a second characteristic impedance in the passband, and at least a third conductor for coupling the second filter to the node.
In addition, according to this aspect of the invention, the apparatus further comprises a switch for alternately coupling the at least first conductor and the at least third conductor to the node.
Additionally according to this aspect of the invention, the apparatus further comprises a fourth conductor for coupling the second filter to the third port.
Illustratively according to both aspects of the invention, the CATV circuit is the return circuit of a two-way CATV system from the subscriber taps to a CATV system headend, and the signal is noise entering the CATV system return path at a node between two adjacent return path amplifiers.
REFERENCES:
patent: 1321543 (1919-11-01), Niswonger
patent: 3731203 (1973-05-01), Lieberman
patent: 3750022 (1973-07-01), Curry et al.
patent: 3846703 (1974-11-01), Stewart et al.
patent: 3886454 (1975-05-01), Oakley et al.
patent: 3924187 (1975-12-01), Dormans
patent: 3991363 (1976-11-01), Lathrop
patent: 4413229 (1983-11-01), Grant
patent: 4480251 (1984-10-01), McNaughton et al.
patent: 4491968 (1985-01-01), Shimp et al.
patent: 4520508 (1985-05-01), Reichert, Jr.
patent: 4920533 (1990-04-01), Dufresne et al.
patent: 4982440 (1991-01-01), Dufresne et al.
patent: 5020134 (1991-05-01), Pecaut
patent: 5126840 (1992-06-01), Dufresne et al.
patent: 5208665 (1993-05-01), McCalley et al.
patent: 5251324 (1993-10-01), McMullan, Jr.
patent: 5255086 (1993-10-01), McMullan et al.
patent: 5473361 (1995-12-01), Penney
patent: 5608328 (1997-03-01), Sanderson
patent: 5608428 (1997-03-01), Bush
patent: 5867206 (1999-02-01), Voight et al.
patent: 5881362 (1999-03-01), Eldering et al.
patent: 5966410 (1999-10-01), Freyman et al.
pa
Barnes & Thornburg
Brown Reuben M.
Faile Andrew
Trilithic, Inc.
LandOfFree
Return path ingress in a two-way CATV system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Return path ingress in a two-way CATV system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Return path ingress in a two-way CATV system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2524603