High resolution time domain reflectometry (TDR) in fault location measurement in a cable network

1 . A test instrument connectable to a cable television (CATV) network to provide a time domain reflectometry (TDR) in a fault location measurement, the test instrument comprising:

a port connectable to a test point of the CATV network; and

a processing circuit to:

transmit, into the test point of the CATV network, a first TDR waveform having frequency-chirped probe pulses, wherein the frequency-chirped probe pulses are formed by an oscillatory signal that oscillates at a varying oscillation frequency to form a width of each pulse, and wherein, during the width of each pulse, the varying oscillation frequency of the oscillatory signal increases from a minimum frequency to a maximum frequency of a frequency band;

monitor to receive a first return signal of the frequency-chirped probe pulses;

use the first return signal to identify impedance changes at a fault location in the CATV network;

perform a first fault location measurement by transmitting the frequency-chirped probe pulses at a first sampling rate into the test point of the CATV network;

perform a first calibration measurement by transmitting the frequency-chirped probe pulses at the first sampling rate into a closed calibration circuit within the test instrument; and

perform a second fault location measurement at a second sampling rate and a second calibration measurement at the second sampling rate that is higher than the first sampling rate.

2 . The test instrument of claim 1 , wherein the processing circuit is further to:

determine a distance from the test point to the fault location in the CATV network based on a measure of time elapsed between the transmitting of the first TDR waveform and the receiving of the first return signal, and a speed of propagation of the frequency-chirped probe pulses in the CATV network.

3 . The test instrument of claim 1 , wherein the processing circuit is further to:

determine a resolution of the frequency-chirped probe pulses based on a propagation speed of the frequency-chirped probe pulses in the CATV network and a value of the frequency band between the maximum frequency and the minimum frequency.

4 . The test instrument of claim 1 , wherein the processing circuit is further to:

generate an identification of the fault location in the CATV network to an output.

5 . The test instrument of claim 1 , wherein the processing circuit is further to:

cross-correlate the second fault location measurement at the second sampling rate with the second calibration measurement at the second sampling rate to generate a cross-correlation TDR waveform;

generate a new TDR waveform using a refinement processing technique to remove echoes from the cross-correlation TDR waveform; and

provide the new TDR waveform to an output, wherein the new TDR waveform is a high resolution TDR waveform associated with the fault location in the CATV network.

6 . The test instrument of claim 5 , wherein the processing circuit is to:

filter out artifacts during the performance of the second calibration measurement.

7 . The test instrument of claim 5 , wherein the refinement processing technique comprises:

identifying a highest peak in the cross-correlation TDR waveform;

determining a time value and an amplitude of the highest peak;

converting the time value that corresponds with the highest peak into a delay factor;

delaying the second calibration measurement by the delay factor; and

scaling the second fault location measurement by the delayed second calibration measurement by a specific correlation.

8 . A method for providing a time domain reflectometry (TDR) in a fault location measurement in a cable television (CATV) network, comprising:

transmitting, by a processor of a test instrument, a first TDR waveform having frequency-chirped probe pulses into a test point of the CATV network, wherein the frequency-chirped probe pulses are formed by an oscillatory signal that oscillates at a varying oscillation frequency to form a width of each pulse, and wherein, during the width of each pulse, the varying oscillation frequency of the oscillatory signal increases from a minimum frequency to a maximum frequency of a frequency band;

monitoring, by the processor, to receive a first return signal of the frequency-chirped probe pulses;

using, by the processor, the first return signal to identify impedance changes at a fault location in the CATV network;

performing, by the processor, a first fault location measurement by transmitting the frequency-chirped probe pulses at a first sampling rate into the test point of the CATV network;

performing, by the processor, a first calibration measurement by transmitting the frequency-chirped probe pulses at the first sampling rate into a closed calibration circuit within the test instrument; and

performing, by the processor, a second fault location measurement at a second sampling rate and a second calibration measurement at the second sampling rate that is higher than the first sampling rate.

9 . The method of claim 8 , further comprising:

determining a distance from the test point to the fault location in the CATV network based on a measure of time elapsed between the transmitting of the first TDR waveform and the receiving of the first return signal, and a speed of propagation of the frequency-chirped probe pulses in the CATV network.

10 . The method of claim 8 , further comprising:

determining a resolution of the frequency-chirped probe pulses based on a propagation speed of the frequency-chirped probe pulses in the CATV network and a value of the frequency band between the maximum frequency and the minimum frequency.

11 . The method of claim 8 , further comprising:

generating an identification of the fault location in the CATV network to an output.

12 . The method of claim 8 , further comprising:

cross-correlating the second fault location measurement at the second sampling rate with the second calibration measurement at the second sampling rate to generate a cross-correlation TDR waveform;

generating a new TDR waveform using a refinement processing technique to remove echoes from the cross-correlation TDR waveform; and

providing the new TDR waveform to an output, wherein the new TDR waveform is a high resolution TDR waveform associated with the fault location in the CATV network.

13 . The method of claim 12 , further comprising:

storing the first calibration measurement and the second calibration measurement in a memory.

14 . The method of claim 12 , further comprising:

filtering out artifacts during the performance of the second calibration measurement.

15 . The method of claim 12 , wherein the refinement processing technique comprises:

identifying a highest peak in the cross-correlation TDR waveform;

determining a time value and an amplitude of the highest peak;

converting the time value that corresponds with the highest peak into a delay factor;

delaying the second calibration measurement by the delay factor; and

scaling the second fault location measurement by the delayed second calibration measurement by a specific correlation.

16 . A non-transitory computer-readable storage medium storing instructions that, when executed by a processor of a test instrument, cause the processor to:

transmit a first time domain reflectometry (TDR) waveform having frequency-chirped probe pulses into a test point of a cable television (CATV) network, wherein the frequency-chirped probe pulses are formed by an oscillatory signal that oscillates at a varying oscillation frequency to form a width of each pulse, and wherein, during the width of each pulse, the varying oscillation frequency of the oscillatory signal increases from a minimum frequency to a maximum frequency of a frequency band;

monitor to receive a first return signal of the frequency-chirped probe pulses;

use the first return signal in a TDR technique to identify impedance changes at a fault location in the CATV network;

perform a first fault location measurement by transmitting the frequency-chirped probe pulses at a first sampling rate into the test point of the CATV network;

perform a first calibration measurement by transmitting the frequency-chirped probe pulses at the first sampling rate into a closed calibration circuit within the test instrument; and

perform a second fault location measurement at a second sampling rate and a second calibration measurement at the second sampling rate that is higher than the first sampling rate.

17 . The non-transitory computer-readable storage medium of claim 16 , wherein the instructions further cause the processor to:

determine a distance from the test point to the fault location in the CATV network based on a measure of time elapsed between the transmitting of the first TDR waveform and the receiving of the first return signal, and a speed of propagation of the frequency-chirped probe pulses in the CATV network.

18 . The non-transitory computer-readable storage medium of claim 16 , wherein the instructions further cause the processor to:

determine a resolution of the frequency-chirped probe pulses based on a propagation speed of the frequency-chirped probe pulses in the CATV network and a value of the frequency band between the maximum frequency and the minimum frequency.

19 . The non-transitory computer-readable storage medium of claim 16 , wherein the instructions further cause the processor to:

cross-correlate the second fault location measurement at the second sampling rate with the second calibration measurement at the second sampling rate to generate a cross-correlation TDR waveform;

generate a new TDR waveform using a refinement processing technique to remove echoes from the cross-correlation TDR waveform; and

provide the new TDR waveform to an output, wherein the new TDR waveform is a high resolution TDR waveform associated with the fault location in the CATV network.

20 . The non-transitory computer-readable storage medium of claim 19 , wherein the refinement processing technique comprises:

identifying a highest peak in the cross-correlation TDR waveform;

determining a time value and an amplitude of the highest peak;

converting the time value that corresponds with the highest peak into a delay factor;

delaying the second calibration measurement by the delay factor; and

scaling the second fault location measurement by the delayed second calibration measurement by a specific correlation.