Doppler location of signal leaks in an HFC network

A method of locating a leak in a Hybrid Fiber-Coax (HFC) network extending over a geographic area, the leak emitting a leakage signal over-the-air, the leakage signal including first and second pilot signals having first and second harmonics, respectively, the first harmonic being defined by a first nominal frequency and having a first actual frequency that deviates from the first nominal frequency by a frequency error, the second harmonic being defined by a second nominal frequency and having a second actual frequency that deviates from the second nominal frequency by about the frequency error, said method comprising the steps of:

• (a) moving through the geographic area of the HFC network, along a drive route;
• (b) at each of a plurality of drive-route points along the drive route, receiving the first and the second harmonics at first and second receive frequencies, respectively;
• (c) for each drive-route point, measuring the first and the second receive frequencies of the first and the second harmonics;
• (d) for each drive-route point, determining a first measured Doppler shift value from the first receive frequency and the first nominal frequency of the first harmonic, and determining a second measured Doppler shift value from the second receive frequency and the second nominal frequency of the second harmonic;
• (e) determining a value of the frequency error and using the value of the frequency error as an estimate of a zero measured Doppler shift value;
• (f) estimating a zero Doppler shift point where the zero Doppler shift value occurs, based on at least the first and the second measured Doppler shift values determined for the plurality of drive-route points;
• and
• (g) estimating a location of the leak based on at least the estimated zero Doppler shift point.

A method of locating a leak in a Hybrid Fiber-Coax (HFC) network extending over a geographic area, the leak emitting a leakage signal over-the-air, the leakage signal including first and second pilot signals having first and second harmonics, respectively, the first harmonic being defined by a first nominal frequency and having a first actual frequency that deviates from the first nominal frequency by a frequency error, the second harmonic being defined by a second nominal frequency and having a second actual frequency that deviates from the second nominal frequency by about the frequency error, said method comprising the steps of:

• (a) moving through the geographic area of the HFC network, along a drive route, at one or more speeds of movement;
• (b) recording a speed of movement at each of a plurality of drive-route points along the drive route;
• (c) at each drive-route point, receiving the first and the second harmonics at first and second receive frequencies, respectively;
• (d) for each drive-route point, measuring the first and the second receive frequencies of the first and the second harmonics;
• (e) for each drive-route point, determining a measured Doppler shift value from (1) a first difference between the first receive frequency and the first nominal frequency of the first harmonic, or (2) the first difference and a second difference between the second receive frequency and the second nominal frequency of the second harmonic;
• (f) for each drive-route point, repeating steps (c), (d) and (e) a plurality of times to produce a plurality of measured Doppler shift values for each drive-route point;
• (g) for each drive-route point, averaging the plurality of measured Doppler shift values to produce an averaged Doppler shift value;
• (h) determining a value of the frequency error and using the value of the frequency error as an estimate of a zero measured Doppler shift value;
• (i) estimating a zero Doppler shift point where the zero measured Doppler shift value occurs, based on at least the averaged Doppler shift values of the plurality of drive-route points;
• and
• (j) estimating a location of the leak based on at least the estimated zero Doppler shift point.