High Resolution TDR Fault Location in Cable Networks
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Solution Overview
Problem
Conventional time domain reflectometry (TDR) techniques require disconnecting service to locate impedance changes in cable television networks, causing customer dissatisfaction and reluctance from service providers due to interference with downstream signals and obscured reflections.
Innovation Solution
Implementing high resolution TDR using frequency-chirped probe pulses that spread pulse energy over a longer time period, reducing interference and increasing signal-to-noise ratio, allowing for in-service fault location without disconnecting service.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional TDR techniques are used to locate impedance changes, then fault location measurement is achieved, but service must be disconnected causing customer dissatisfaction and interference with downstream signals
Solution Approach 1:
The patent transforms the conventional impulse TDR signal into a frequency-chirped continuous wave signal, changing the temporal parameter from short-duration pulse to extended-duration signal. This parameter transformation allows the measurement to proceed without disconnecting service, as the chirped signal's energy is distributed over time and frequency, reducing peak interference with downstream signals while maintaining fault location capability through frequency-to-distance mapping
Solution Approach 2:
The patent replaces the mechanical/discrete impulse signal injection method with a continuous frequency-modulated wave approach. Instead of using a sudden electrical impulse that causes signal interference, the system uses a chirped continuous wave that can coexist with downstream signals, substituting the traditional TDR signal generation mechanism with a frequency-modulated continuous wave technique that enables in-service measurements
2Measurement precision
If conventional TDR impulse signals are used, then fault location is determined, but interference with downstream signals and obscured reflections occur
Solution Approach 1:
The patent employs a continuous periodic chirped signal instead of a single impulse, using frequency modulation over time to probe the network. The periodic nature of the chirped signal allows for coherent integration of reflections over multiple cycles, improving signal-to-noise ratio and enabling detection of weak reflections that would be obscured by impulse signal interference with downstream communications
Solution Approach 2:
The chirped continuous wave acts as an intermediary between the TDR measurement function and the live cable network. By spreading the measurement energy across a frequency spectrum and time duration, the chirped signal mediates between the need for accurate fault location and the requirement to avoid interfering with downstream signals, allowing measurements to proceed without causing harmful interference
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate and reliable in-service fault location in cable networks with improved range resolution and signal quality, aligning with out-of-service measurement accuracy without service disruption.
Implementation Method 1
frequency-chirped probe pulses that spread pulse energy over a longer time period, reducing interference and increasing signal-to-noise ratio
Implementation Method 2
time domain reflectometry (TDR) techniques require disconnecting service to locate impedance changes in cable television networks
Data Source
AI summary
A test instrument connectable to a cable television (CATV) network to provide a high resolution time domain reflectometry (TDR) in a fault location measurement is disclosed. The test instrument may have a port connectable to a test point in the CATV network. The test instrument may also have a processing circuit to perform a calibration measurement and a fault location measurement by, for the calibration measurement, transmitting frequency-chirped probe pulses into a closed calibration circuit within the test instrument, and receiving return signals at an analog-digital converter in the test instrument. The processing circuit may also resample the calibration measurement and the fault location measurement at a high sampling rate, cross-correlate the fault location with the calibration measurement to generate a cross-correlation TDR waveform, and generate a new TDR waveform using a refinement processing technique to remove echoes from the cross-correlation TDR waveform.