System and method to locate common path distortion on cable systems

• US 20080319689A1
• Filed: 07/07/2008
• Published: 12/25/2008
• Est. Priority Date: 05/20/2003
• Status: Active Grant

• Current Assignee: Arcom Digital Patent, LLC
• Original Assignee: Arcom Digital, LLC
• Inventors: Williams, Thomas Holtzman
• Granted Patent: US 7,788,050 B2
• Time in Patent Office: Days
• US Class Current: 702/59
• CPC Class Codes: H04N 17/00 Diagnosis, testing or measuring for television systems or their details

Abstract

A system and method to range a distance to a source of CPD on a two-way cable system, comprises a fixed CW signal injected into a downstream signal path, a swept signal transmitted from a network analyzer, a mixer for generating an up-converted swept signal, and a source of CPD in the two-way cable system that mixes the fixed CW signal and the swept signal to create an upstream swept signal. The network analyzer receives the upstream swept signal and determines a complex frequency response created by the source of CPD. An impulse response is determined from the complex frequency response, and the distance to the source of CPD is determined from the impulse response.

Claims

1. A system to range a distance to a source of CPD on a two-way cable system comprising:

a fixed CW signal injected into a downstream signal path;

a swept signal transmitted from a network analyzer;

a mixer for generating an up-converted swept signal; and

a source of CPD in the two-way cable system that mixes the fixed CW signal and the up-converted swept signal to create an upstream swept signal;

wherein the network analyzer receives the upstream swept signal and determines a complex frequency response created by the source of CPD, an impulse response is determined from the complex frequency response, and the distance to the source of CPD is determined from the impulse response.

2. A system according to claim 1 wherein the frequency conversion occurs on an upstream receive leg of the two-way cable system.

3. A system to range a distance to a source of CPD on a two-way cable system comprising:

a fixed CW signal injected into a downstream signal path;

a tunable CW signal injected into the downstream signal path;

a source of CPD in the two-way cable system that mixes the fixed CW signal and the tunable CW signal to create an upstream CW signal;

a first mixer for creating a mixing CW signal by mixing the fixed CW signal and the tunable CW signal;

a second mixer for mixing the received upstream CW signal with the mixing CW signal to create a DC voltage; and

a DC voltage-measuring device for displaying voltage cycles as a frequency of the tunable CW signal is varied;

wherein a round-trip travel time is determined from a frequency difference between voltage peaks on the DC voltage-measuring device, and the distance to the source of CPD is determined from a round-trip travel time.

4. A system to range a distance to a source of CPD on a two-way cable system comprising:

a fixed CW signal injected into a downstream portion of the two-way cable system;

an up-converted tunable signal injected into the downstream cable system;

a source of CPD in the two-way cable system that mixes the fixed CW signal and the up-converted tunable signal to produce a mixed upstream signal;

an in-phase mixer for mixing a tunable sine wave signal with the mixed upstream signal to create an in-phase output line;

a quadrature mixer for mixing a tunable cosine wave signal with the mixed upstream signal to create a quadrature output line; and

a voltage-measuring device for capturing voltages on the in-phase output line and the quadrature output line as the frequency of the tunable sine wave and cosine wave signals are varied;

wherein a record of voltage measurements from the in-phase output line and the quadrature output line determines a complex frequency response created by the source of CPD, an impulse response is determined from the complex frequency response, and the distance to a source of CPD is determined from the impulse response.

5. A system according to claim 4 further comprising a computer to automate capturing of in-phase and quadrature voltages and to control tuning of a tunable signal generator.