Methods and apparatus for detecting and locating leakage of digital signals

• US 20110043640A1
• Filed: 08/18/2009
• Published: 02/24/2011
• Est. Priority Date: 08/18/2009
• Status: Active Grant

• Current Assignee: Arcom Digital Patent, LLC
• Original Assignee: Arcom Digital, LLC
• Inventors: Zinevich, Victor M.
• Granted Patent: US 8,456,530 B2
• Time in Patent Office: Days
• US Class Current: 348/192
• CPC Class Codes: G01R 31/08 Locating faults in cables, transmission lines, or networks
• CPC Class Codes: G01S 5/06 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/12 takes precedence
• CPC Class Codes: H04H 20/12 Arrangements for observation, testing or troubleshooting
• CPC Class Codes: H04N 17/004 for digital television systems
• CPC Class Codes: H04N 21/2383 Channel coding or modulation of digital bit-stream, e.g. QPSK modulation arrangements for detecting or preventing errors in the information received by adapting the channel coding H04L1/0009; analogue front ends or means for connecting modulators, demodulators or transceivers to a transmission line H04L27/0002
• CPC Class Codes: H04N 21/4382 Demodulation or channel decoding, e.g. QPSK demodulation analog front ends or means for connecting modulators, demodulators or transceivers to a transmission line H04L27/0002
• CPC Class Codes: H04N 21/6118 involving cable transmission, e.g. using a cable modem

Abstract

A system for detecting and locating a digital TV leakage signal in an HFC network. The system comprises a headend unit and a leakage detector. The headend unit receives the TV signal at the headend for use as a reference signal. The reference signal is sampled at a rate corresponding to a time reference signal, to produce reference signal samples. The reference signal samples and timestamp are transmitted to the leakage detector. The detector receives the digital TV signal from a leakage source, for detection as a leakage signal. The detector includes a cross-correlation processor. The leakage signal is sampled at a rate corresponding to the time reference signal, to produce leakage signal samples. The cross-correlation processor performs a cross-correlation of the reference signal samples with the leakage signal samples to produce a cross-correlation function having a peak, and the TV leakage signal is detected from this peak.

Claims

1. A system for detecting a digital TV signal emitted into free space from the coaxial cable portion of an HFC network, said system operating in connection with a time reference signal, a timestamp, and a communications link, the digital TV signal being transmitted in the HFC network from a headend, said system comprising:

a headend unit, including—

an input, adapted to be coupled to the headend, for receiving the digital TV signal from the headend for use as a TV reference signal,

a first receiver for receiving the time reference signal and timestamp,

a first signal sampler, coupled to the input and the first receiver, for sampling the TV reference signal at a rate corresponding to the time reference signal, to produce TV reference signal samples,

a first data processor, coupled to the first signal sampler for receiving the TV reference signal samples, and coupled to the first receiver for receiving the timestamp, said first data processor being adapted to associate the timestamp with the TV reference signal samples, and

a first communications interface, associated with the first data processor and adapted to interface with the communications link for transmission of the TV reference signal samples and the associated timestamp over the communications link; and

a detector unit, including—

an antenna for receiving the digital TV signal emitted in free space from the coaxial portion of the HFC network, for detection as a TV leakage signal,

a second receiver for receiving the time reference signal and timestamp,

a second signal sampler, coupled to the antenna and the second receiver, for sampling the TV leakage signal at a rate corresponding to the time reference signal, to produce TV leakage signal samples,

a second data processor, coupled to the second signal sampler for receiving the TV leakage signal samples, and coupled to the second receiver for receiving the timestamp, said second data processor being adapted to associate the timestamp with the TV leakage signal samples,

a second communications interface associated with the second data processor and adapted to interface with the communications link for reception of the TV reference signal samples and the associated timestamp from the communications link, and adapted to transfer the TV reference signal samples and the associated timestamp to the second data processor, and

a cross-correlation processor, coupled to the second data processor and adapted to perform a cross-correlation of the TV reference signal samples, associated with the timestamp, with the TV leakage signal samples, associated with the same timestamp, to produce a cross-correlation function having a peak,

whereby the TV leakage signal is detected from the peak of the cross-correlation function.

2. The apparatus of claim 1, wherein the second data processor sends the TV reference signal samples and the TV leakage signal samples to the cross-correlation processor after determining that the TV reference signal samples and the TV leakage signal samples are associated with the same timestamp.

3. The apparatus of claim 1, wherein the digital TV signal is a quadrature amplitude modulation TV signal.

4. The apparatus of claim 1, wherein the first receiver is a GPS receiver, and the time reference signal and timestamp are received by the GPS receiver from a GPS system.

5. The apparatus of claim 1, wherein the first signal sampler is an analog-to-digital converter.

6. The apparatus of claim 1, wherein the first data processor is a programmable computer.

7. The apparatus of claim 6, wherein the first communications interface is an Internet browser operating on the programmable computer, and wherein the communications link includes the Internet and a wireless communications network.

8. The apparatus of claim 1, wherein said detector unit is a portable unit to be taken out into the field, in the vicinity of the coaxial cable portion of the HFC network, away from the headend unit.

9. The apparatus of claim 1, wherein the second receiver is a GPS receiver, and the time reference signal and timestamp are received by the GPS receiver from a GPS system.

10. The apparatus of claim 1, wherein the second signal sampler is an analog-to-digital converter.

11. The apparatus of claim 10, wherein the second data processor includes a programmable computer and a data controller, the data controller being coupled between the programmable computer and the analog-to-digital converter and between the programmable computer and the cross-correlation processor.

12. The apparatus of claim 1, wherein the second communications interface includes a wireless modem, and wherein the communications link includes a wireless network.

13. The apparatus of claim 1, wherein the cross-correlation performed by the cross-correlation processor is carried out in the frequency domain.

14. The apparatus of claim 13, wherein the cross-correlation carried out in the frequency domain yields a result that is transformed to the time domain to produce the cross-correlation function.

15. The apparatus of claim 1, wherein the HFC network is a bi-directional communications network having a forward path and a return path, the digital TV signal being transmitted from the headend in the forward path, and wherein the communications link includes the return path of the HFC network, and the first and the second communications interfaces are configured to communicate with the return path.

16. A system for detecting a digital TV signal emitted into free space from the coaxial cable portion of an HFC network, said system operating in connection with a time reference signal, a timestamp, and a communications link, the digital TV signal being transmitted in the coaxial cable portion of the HFC network from a fiber optic node, said system comprising:

a reference unit, including—

an input, adapted to be coupled to a reference point in the HFC network, for receiving the digital TV signal from the reference point for use as a TV reference signal,

a first receiver for receiving the time reference signal and timestamp,

a first signal sampler, coupled to the input and the first receiver, for sampling the TV reference signal at a rate corresponding to the time reference signal, to produce TV reference signal samples,

a first data processor, coupled to the first signal sampler for receiving the TV reference signal samples, and coupled to the first receiver for receiving the timestamp, said first data processor being adapted to associate the timestamp with the TV reference signal samples, and

a first communications interface, associated with the first data processor and adapted to interface with the communications link for transmission of the TV reference signal samples and the associated timestamp over the communications link; and

a detector unit, including—

an antenna for receiving the digital TV signal emitted in free space from the coaxial portion of the HFC network, for detection as a TV leakage signal,

a second receiver for receiving the time reference signal and timestamp,

a second signal sampler, coupled to the antenna and the second receiver, for sampling the TV leakage signal at a rate corresponding to the time reference signal, to produce TV leakage signal samples,

a second data processor, coupled to the second signal sampler for receiving the TV leakage signal samples, and coupled to the second receiver for receiving the timestamp, said second data processor being adapted to associate the timestamp with the TV leakage signal samples,

a second communications interface associated with the second data processor and adapted to interface with the communications link for reception of the TV reference signal samples and the associated timestamp from the communications link, and adapted to transfer the TV reference signal samples and the associated timestamp to the second data processor, and

a cross-correlation processor, coupled to the second data processor and adapted to cross-correlate the TV reference signal samples, associated with the timestamp, with the TV leakage signal samples, associated with the same timestamp, to produce a cross-correlation function having a peak,

whereby the TV leakage signal is detected from the peak of the cross-correlation function.

17. The apparatus of claim 16, wherein the second data processor sends the TV reference signal samples and the TV leakage signal samples to the cross-correlation processor after determining that the TV reference signal samples and the TV leakage signal samples are associated with the same timestamp.

18. The apparatus of claim 16, wherein the reference point in the HFC network is at the fiber optic node.

19. The apparatus of claim 16, wherein the HFC network is a bi-directional communications network having a forward path and a return path, the digital TV signal being transmitted from the headend in the forward path, and wherein the communications link includes the return path of the HFC network, and the first and the second communications interfaces are configured to communicate with the return path.

20. A method of detecting a digital TV signal emitted into free space from the coaxial cable portion of an HFC network, said method operating in connection with a time reference signal, a timestamp, and a communications link, the digital TV signal being transmitted in the HFC network from a headend, said method comprising the steps of:

(a) receiving the digital TV signal from the headend for use as a TV reference signal;

(b) receiving the time reference signal and timestamp;

(c) sampling the TV reference signal at a rate corresponding to the time reference signal, to produce TV reference signal samples;

(d) associating the timestamp with the TV reference signal samples;

(e) transmitting the TV reference signal samples and the associated timestamp over the communications link to a detector unit situated in the vicinity of the coaxial cable portion of the HFC network;

(f) receiving, at the detector unit, the TV reference signal samples and the associated timestamp from the communications link;

(g) receiving, at the detector unit, the digital TV signal emitted in free space from the coaxial cable portion of the HFC network, for detection as a TV leakage signal;

(h) receiving, at the detector unit, the time reference signal and timestamp;

(i) sampling the TV leakage signal at a rate corresponding to the time reference signal, to produce TV leakage signal samples;

(j) associating the timestamp with the TV leakage signal samples; and

(k) performing a cross-correlation of the TV reference signal samples, associated with the timestamp, with the TV leakage signal samples, associated with the same timestamp, to produce a cross-correlation function having a peak,

whereby the TV leakage signal is detected from the peak of the cross-correlation function.

21. The method of claim 20, wherein the digital TV signal is a quadrature amplitude modulation TV signal.

22. The method of claim 20, wherein the HFC network further includes a fiber optic cable portion between the headend and a fiber optic node, the method further comprising the step of:

(l) calibrating the fiber optic node, by measuring a time delay T₁ of the digital TV signal propagating from the headend to the fiber optic node,

the sampling of the TV leakage signal in step (i) being delayed by approximately the time delay T₁ relative the sampling of the TV reference signal in step (c),

whereby the cross-correlation performed in step (k) is simplified, in that the TV leakage signal samples do not include samples taken over the time delay T₁.

23. A method of detecting a digital TV signal emitted into free space from the coaxial cable portion of an HFC network, said method operating in connection with a time reference signal, a timestamp, and a communications link, the digital TV signal being transmitted in the coaxial cable portion of the HFC network from a fiber optic node, said method comprising the steps of:

(a) receiving the digital TV signal from a reference point in the HFC network for use as a TV reference signal;

(b) receiving the time reference signal and timestamp;

(c) sampling the TV reference signal at a rate corresponding to the time reference signal, to produce TV reference signal samples;

(d) associating the timestamp with the TV reference signal samples;

(e) transmitting the TV reference signal samples and the associated timestamp over the communications link to a detector unit situated in the vicinity of the coaxial cable portion of the HFC network;

(f) receiving, at the detector unit, the TV reference signal samples and the associated timestamp from the communications link;

(g) receiving, at the detector unit, the digital TV signal emitted in free space from the coaxial cable portion of the HFC network, for detection as a TV leakage signal;

(h) receiving, at the detector unit, the time reference signal and timestamp;

(i) sampling the TV leakage signal at a rate corresponding to the time reference signal, to produce TV leakage signal samples,

(j) associating the timestamp with the TV leakage signal samples; and

(k) performing a cross-correlation of the TV reference signal samples, associated with the timestamp, with the TV leakage signal samples, associated with the same timestamp, to produce a cross-correlation function having a peak,

whereby the TV leakage signal is detected from the peak of the cross-correlation function.

24. The method of claim 23, wherein the reference point in the HFC network is at the fiber optic node.

25. A method of locating a leakage source in the coaxial cable portion of an HFC network that is defined, at least in part, by a multiplicity of network points, each of the multiplicity of network points being characterized in a network database by geographic coordinates and a time delay value, Tcoax_n, said method comprising the steps of:

(a) detecting, at a detection point, a signal emitted into free space from the leakage source, the signal being transmitted through the coaxial portion of the HFC network from a fiber optic node to the leakage source, the detection point being defined by geographic coordinates;

(b) measuring the propagation delay of the signal from the fiber optic node to the detection point, Tmnd, which includes a coaxial cable propagation delay from the fiber optic node to the leakage source, Tcoax, and a free space propagation delay from the leakage source to the detection point, Tair;

(c) retrieving the geographic coordinates of the multiplicity of network points from the network database;

(d) calculating the distances Rn from the detection point to each of the multiplicity of network points, using the geographic coordinates of the multiplicity of network points and the geographic coordinates of the detection point;

(e) calculating the propagation delay in free space from the detection point to each of the multiplicity of network points, Tair_n, using the distances Rn calculated in step (d) and the velocity of propagation of an electric wave in free space;

(f) retrieving the time delay values, Tcoax_n, of the multiplicity of network points from the network database, the time delay values Tcoax_n being predetermined propagation delays in the coaxial cable portion of the HFC network from the fiber optic node to the multiplicity of network points, respectively;

(g) calculating the propagation delays from the fiber optic node of the HFC network to the detection point, via each of the multiplicity of network points, Tcnd_n, by adding together the delays Tair_n, calculated in step (e), and the values, Tcoax_n, retrieved in step (f), respectively;

(h) comparing the delays Tcnd_n calculated in step (g) with the delay Tmnd measured in step (b), and selecting a delay Tcnd_k from the delays Tcnd_n that substantially matches, within a tolerance value, the delay Tmnd; and

(i) identifying a network point from the delay Tcnd_k selected in step (h), as a candidate of the leakage source.

26. The method of claim 25, further comprising the step of:

(j) identifying the location of the candidate of the leakage source by retrieving the geographic coordinates of the network point identified in step (i).

27. The method of claim 26, further comprising the step of:

(k) representing the location of the candidate identified in step (j) on an electronic map of the HFC network, by use of a marker or other symbol.

28. The method of claim 25, wherein at least one of the multiplicity of network points is a network device connected in the coaxial cable portion of the HFC network.

29. The method of claim 25, wherein the signal emitted into free space from the leakage source is transmitted through the HFC network from a headend, and wherein the detection of the signal in step (a) is performed by coherent cross-correlation of the signal sampled at the headend with the signal sampled at the detection point.

30. The method of claim 25, wherein the detection of the signal in step (a) is performed by coherent cross-correlation of the signal sampled at a reference point in the coaxial cable portion of the HFC network with the signal sampled at the detection point.

31. A method of locating a leakage source in the coaxial cable portion of an HFC network, the location of the leakage source being defined by a set of geographic coordinates, said method comprising the steps of:

(a) detecting, at a first detection point, a signal emitted into free space from the leakage source, the signal being transmitted through the coaxial portion of the HFC network from a fiber optic node to the leakage source, the first detection point being defined by a first set of geographic coordinates;

(b) measuring a first propagation delay of the signal, t1, which includes at least the propagation delay from the leakage source to the first detection point;

(c) detecting, at a second detection point, the signal emitted into free space from the leakage source, the second detection point being defined by a second set of geographic coordinates;

(d) measuring a second propagation delay of the signal, t2, which includes at least the propagation delay from the leakage source to the second detection point;

(e) detecting, at a third detection point, the signal emitted into free space from the leakage source, the third detection point being defined by a third set of geographic coordinates;

(f) measuring a third propagation delay of the signal, t3, which includes at least the propagation delay from the leakage source to the third detection point;

(g) calculating the time difference, Δ

t12, between the first delay t1 and the second delay t2, and the time difference, Δ

t23, between the second delay t2 and the third delay t3; and

(h) determining the approximate location of the leakage source by solving for the set of geographic coordinates of the leakage source in at least two hyperbolic equations defined by the time differences Δ

t12 and Δ

t23 and by the first, second and third sets of geographic coordinates.

32. The method of claim 31, further comprising the step of:

(i) representing the approximate location of the leakage source determined in step (h) on an electronic map of the HFC network, by use of a marker or other symbol.

33. The method of claim 31, further comprising the steps of:

(i) retrieving the first set of geographic coordinates from a GPS system at the first detection point;

(j) retrieving the second set of geographic coordinates from the GPS system at the second detection point; and

(k) retrieving the third set of geographic coordinates from the GPS system at the third detection point.

34. The method of claim 31, wherein the signal emitted into free space from the leakage source is transmitted through the HFC network from a headend, and wherein the detection of the signal in steps (a), (c) and (e) are performed by coherent cross-correlation of the signal sampled at the headend with the signal sampled at the first, second and third detection points, respectively.

35. The method of claim 31, wherein the detection of the signal in steps (a), (c) and (e) are performed by coherent cross-correlation of the signal sampled at a reference point in the coaxial cable portion of the HFC network with the signal sampled at the first, second and third detection points, respectively.

36. A method of locating a leakage source in the coaxial cable portion of an HFC network that is defined, at least in part, by a multiplicity of network points, each of the multiplicity of network points being characterized in a network database by geographic coordinates and a time delay value, Tcoax_n, and the location of the leakage source being defined by a set of geographic coordinates, said method comprising the steps of:

(a) detecting, at a first detection point, a signal emitted into free space from the leakage source, the signal being transmitted through the coaxial cable portion of the HFC network from a fiber optic node to the leakage source, the first detection point being defined by a first set of geographic coordinates;

(b) measuring a first propagation delay of the signal from the fiber optic node to the first detection point, Tmnd₁, which includes a coaxial cable propagation delay from the fiber optic node to the leakage source, Tcoax, and a free space propagation delay from the leakage source to the first detection point, Tair;

(c) retrieving the geographic coordinates of the multiplicity of network points from the network database;

(d) calculating the distances Rn from the first detection point to each of the multiplicity of network points, using the geographic coordinates of the multiplicity of network points and the geographic coordinates of the first detection point;

(e) calculating the propagation delay in free space from the first detection point to each of the multiplicity of network points, Tair_n, using the distances Rn calculated in step (d) and the velocity of propagation of an electric wave in free space;

(f) retrieving the time delay values, Tcoax_n, of the multiplicity of network points from the network database, the time delay values Tcoax_n being predetermined propagation delays in the coaxial cable portion of the HFC network from the fiber optic node to the multiplicity of network points, respectively;

(g) calculating the propagation delay from the fiber optic node of the HFC network to the first detection point, via each of the multiplicity of network points, Tcnd_n, by adding together the delays Tair_n, calculated in step (e), and the delays Tcoax_n, retrieved in step (f), respectively;

(h) comparing the delays Tcnd_n calculated in step (g) with the delay Tmnd₁ measured in step (b), and selecting a delay Tcnd_k from the delays Tcnd_n that substantially matches, within a tolerance value, the delay Tmnd₁;

(i) identifying a network point from the delay Tcnd_k selected in step (h), as a first candidate of the leakage source;

(j) detecting, at a second detection point, the signal emitted into free space from the leakage source, the second detection point being defined by a second set of geographic coordinates;

(k) measuring a second propagation delay of the signal, Tmnd₂, which includes at least the propagation delay from the leakage source to the second detection point;

(l) detecting, at a third detection point, the signal emitted into free space from the leakage source, the third detection point being defined by a third set of geographic coordinates;

(m) measuring a third propagation delay of the signal, Tmnd₃, which includes at least the propagation delay from the leakage source to the third detection point;

(n) calculating the time difference, Δ

t12, between the first delay Tmnd₁ and the second delay Tmnd₂, and the time difference, Δ

t23, between the second delay Tmnd₂ and the third delay Tmnd₃; and

(o) determining the approximate location of the leakage source by solving for the set of geographic coordinates of the leakage source in at least two hyperbolic equations defined by the time differences Δ

t12 and Δ

t23 and by the first, second and third sets of geographic coordinates.

37. The method of claim 36, further comprising the step of:

(p) comparing the geographic coordinates of the leakage source determined in step (o) with the geographic coordinates of the first candidate of the leakage source identified in step (i).

38. The method of claim 36, further comprising the step of:

(p) comparing the set of geographic coordinates of the leakage source determined in step

(o) with the geographic coordinates of the multiplicity of network points stored in the network database, to find a match, within a tolerance value, and identify a second candidate of the leakage source.

39. The method of claim 38, further comprising the step of:

(q) comparing the first candidate of the leakage source with the second candidate of the leakage source.

40. A method of detecting a low frequency ingress source in a bi-directional HFC network carrying digital TV signals in a forward path and having a low frequency return path, the low frequency ingress source admitting low frequency ingress into the return path, said method operating in connection with a time reference signal, a timestamp, and a communications link, said method comprising the steps of:

(a) receiving a digital TV signal having a center frequency in the VHF Low Band of the forward path, and selecting the digital TV signal for use as a TV reference signal;

(b) receiving the time reference signal and timestamp;

(c) sampling the TV reference signal at a rate corresponding to the time reference signal, to produce TV reference signal samples;

(d) associating the timestamp with the TV reference signal samples;

(e) transmitting the TV reference signal samples and the associated timestamp over the communications link to a detector unit situated in the vicinity of the coaxial cable portion of the HFC network;

(f) receiving, at the detector unit, the TV reference signal samples and the associated timestamp from the communications link;

(g) receiving, at the detector unit, the digital TV signal emitted in free space from the source of low frequency ingress, for detection as a TV egress signal;

(h) receiving, at the detector unit, the time reference signal and timestamp;

(i) sampling the TV egress signal at a rate corresponding to the time reference signal, to produce TV egress signal samples;

(j) associating the timestamp with the TV leakage signal samples;

(k) performing a cross-correlation of the TV reference signal samples, associated with the timestamp, with the TV egress signal samples, associated with the same timestamp, to produce a cross-correlation function having a peak; and

(l) detecting the TV egress signal from the peak of the cross-correlation function, whereby the detection of the TV egress signal indicates a detection of the ingress source.

41. The method of claim 40, wherein the digital TV signal received in step (a) has a center frequency within channel 2, within the range of 54 to 60 MHz.

42. A method of locating a low frequency ingress source in a bi-directional HFC network carrying digital TV signals in a forward path and having a low frequency return path, the low frequency ingress source admitting low frequency ingress into the return path, the HFC network being defined, at least in part, by a headend, a fiber optic node, a coaxial cable portion, and a multiplicity of network points in the coaxial cable portion, each of the multiplicity of network points being characterized in a network database by geographic coordinates and a time delay value, Tcoax_n, said method comprising the steps of:

(a) detecting, at a detection point, a digital TV signal emitted into free space from the low frequency ingress source and received at the detection point, the digital TV signal having a center frequency in the VHF Low Band of the forward path and being transmitted through the HFC network from the headend, the detection being performed by coherent cross-correlation of the digital TV signal from the headend with the digital TV signal received at the detection point, the detection point being defined by geographic coordinates;

(b) measuring the propagation delay of the digital TV signal from the fiber optic node to the detection point, Tmnd, which includes a coaxial cable propagation delay from the fiber optic node to the ingress source, Tcoax, and a free space propagation delay from the ingress source to the detection point, Tair;

(c) retrieving the geographic coordinates of the multiplicity of network points from the network database;

(d) calculating the distances Rn from the detection point to each of the multiplicity of network points, using the geographic coordinates of the multiplicity of network points and the geographic coordinates of the detection point;

(e) calculating the propagation delay in free space from the detection point to each of the multiplicity of network points, Tair_n, using the distances Rn calculated in step (d) and the velocity of propagation of an electric wave in free space;

(f) retrieving the time delay values, Tcoax_n, of the multiplicity of network points from the network database, the values Tcoax_n being predetermined propagation delays in the coaxial cable portion of the HFC network from the fiber optic node to the multiplicity of network points, respectively;

(g) calculating the propagation delays from the fiber optic node of the HFC network to the detection point, via each of the multiplicity of network points, Tcnd_n, by adding together the delays Tair_n, calculated in step (e), and the delays Tcoax_n, calculated in step (f), respectively;

(h) comparing the delays Tcnd_n calculated in step (g) with the delay Tmnd measured in step (b), and selecting a delay Tcnd_k from the delays Tcnd_n that substantially matches, within a tolerance value, the delay Tmnd; and

(i) identifying a network point from the delay Tcnd_k selected in step (h), as a candidate of the low frequency ingress source.

43. A method of locating a low frequency ingress source in a bi-directional HFC network carrying digital TV signals in a forward path and having a low frequency return path, the low frequency ingress source admitting low frequency ingress into the return path, the location of the ingress source being defined by a set of geographic coordinates, the HFC network being defined, at least in part, by a headend, a fiber optic node, and a coaxial cable portion, said method comprising the steps of:

(a) detecting, at a first detection point, a digital TV signal emitted into free space from the ingress source and received at the first detection point, the digital TV signal having a center frequency in the VHF Low Band of the forward path and being transmitted through the coaxial cable portion of the HFC network from the fiber optic node to the ingress source, the detection being performed by coherent cross-correlation of the digital TV signal from the headend with the digital TV signal received at the first detection point, the first detection point being defined by a first set of geographic coordinates;

(b) measuring a first propagation delay of the digital TV signal, t1, which includes at least the propagation delay from the ingress source to the first detection point;

(c) detecting, at a second detection point, the digital TV signal emitted into free space from the ingress source and received at the second detection point, the detection being performed by coherent cross-correlation of the digital TV signal from the headend with the digital TV signal received at the second detection point, the second detection point being defined by a second set of geographic coordinates;

(d) measuring a second propagation delay of the digital TV signal, t2, which includes at least the propagation delay from the ingress source to the second detection point;

(e) detecting, at a third detection point, the digital TV signal emitted into free space from the ingress source and received at the third detection point, the detection being performed by coherent cross-correlation of the digital TV signal from the headend with the digital TV signal received at the third detection point, the third detection point being defined by a third set of geographic coordinates;

(f) measuring a third propagation delay of the digital TV signal, t3, which includes at least the propagation delay from the ingress source to the third detection point;

(g) calculating the time difference, Δ

t12, between the first delay t1 and the second delay t2, and the time difference, Δ

t23, between the second delay t2 and the third delay t3; and

(h) determining the approximate location of the low frequency ingress source by solving for the set of geographic coordinates of the ingress source in at least two hyperbolic equations defined by the time differences Δ

t12 and Δ

t23 and by the first, second and third sets of geographic coordinates.