System and method to locate common path distortion on cable systems

• US 7,788,050 B2
• Filed: 07/07/2008
• Issued: 08/31/2010
• Est. Priority Date: 05/20/2003
• Status: Active Grant

• Current Assignee: Arcom Digital Patent, LLC
• Original Assignee: Arcom Digital, LLC
• Inventors: Williams, Thomas Holtzman
• Primary Examiner(s): Charioui; Mohamed
• Application Number:
  US12/217,547
• Publication Number:
  US 20080319689A1
• Time in Patent Office: 785 Days
• Field of Search: 702 57- 60, 702/64, 702/65, 702/69, 702/79, 702/82, 702/182, 702/183, 702/185, 702/190, 455/189.1, 455/209, 455/293, 455/326, 455/456.1
• 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 method of ranging a distance to a source of common path distortion in a two-way cable system that has a downstream signal path and an upstream signal path, said method comprising the steps of:

(a) generating a fixed frequency signal for transmission in the downstream signal path of the cable system;

(b) generating a first swept frequency signal, having a first swept bandwidth, for transmission in the downstream signal path of the cable system;

(c) transmitting the fixed frequency signal and the first swept frequency signal in the downstream signal path of the cable system;

(d) receiving a second swept frequency signal from the upstream signal path of the cable system, the second swept frequency signal having a second swept bandwidth and being created by the source of common path distortion by a mixing action of the fixed frequency signal with the first swept frequency signal, the second swept bandwidth of the second swept frequency signal being approximately equal to the first swept bandwidth of the first swept frequency signal;

(e) determining a complex frequency response associated with the second swept frequency signal;

(f) determining an impulse response from the complex frequency response and obtaining a time delay from the impulse response, the time delay being associated with the source of common path distortion; and

(g) determining the distance to the source of common path distortion from the time delay.

2. A method according to claim 1, wherein step (b) further includes—

(i) generating an intermediate swept frequency signal having a swept bandwidth, and

(ii) up-converting the intermediate swept frequency signal to form the first swept frequency signal.

3. A method according to claim 2, wherein step (i) includes generating the intermediate swept frequency signal using a network analyzer.

4. A method according to claim 3, wherein step (d) includes receiving the second swept frequency signal in the network analyzer.

5. A method according to claim 2, wherein the swept bandwidth of the intermediate swept frequency signal is approximately equal to the first swept bandwidth of the first swept frequency signal.

6. A method according to claim 2, wherein the intermediate swept frequency signal sweeps in frequency from a first intermediate frequency to a second intermediate frequency, and wherein the second swept frequency signal sweeps in frequency from a first upstream frequency to a second upstream frequency, the first intermediate frequency being approximately equal to the first upstream frequency and the second intermediate frequency being approximately equal to the second upstream frequency.

7. A method according to claim 1, wherein step (b) includes generating the first swept frequency signal using a network analyzer.

8. A method according to claim 7, wherein step (e) includes determining the complex frequency response using the network analyzer.

9. A method according to claim 8, wherein step (f) includes determining the impulse response using the network analyzer.

10. A method according to claim 1, wherein the first swept frequency signal is generated in step (b) solely by a network analyzer.

11. A method according to claim 10, wherein the first swept frequency signal sweeps in frequency from a first downstream frequency to a second downstream frequency, and wherein the second swept frequency signal sweeps in frequency from a first upstream frequency to a second upstream frequency, and

wherein step (d) further includes up-converting the second swept frequency signal such that the first and second upstream frequencies of the second swept frequency signal are converted to approximately the first and second downstream frequencies of the first swept frequency signal, respectively.

12. A method according to claim 1, wherein step (a) includes generating a fixed frequency continuous wave signal.

13. A method according to claim 1, wherein the first swept bandwidth of the first swept frequency signal is at least 25 MHz, and wherein the second swept bandwidth of the second swept frequency signal is at least 25 MHz.

14. A method of ranging a distance to a source of common path distortion in a two-way cable system that has a downstream signal path and an upstream signal path, said method comprising the steps of:

(a) generating a first downstream signal having a fixed frequency, for transmission in the downstream signal path of the cable system;

(b) generating a second downstream signal having a tunable frequency varying between first and second downstream frequencies, for transmission in the downstream signal path of the cable system;

(c) transmitting the first and the second downstream signals in the downstream signal path of the cable system;

(d) receiving an upstream signal from the upstream signal path of the cable system, the upstream signal being created by the source of common path distortion by a mixing action of the first downstream signal with the second downstream signal, the upstream signal varying in frequency between first and second upstream frequencies in accordance with a variation in frequency between first and second downstream frequencies, respectively, of the second downstream signal;

(e) generating in-phase and quadrature mixing signals, each varying in frequency between the first and the second upstream frequencies in accordance with the variation in frequency between the first and the second downstream frequencies, respectively, of the second downstream signal, the quadrature mixing signal being shifted in phase relative to the in-phase mixing signal by about 90 degrees;

(f) mixing the upstream signal with the in-phase mixing signal to produce an in-phase voltage level, and mixing the upstream signal with the quadrature mixing signal to produce a quadrature voltage level, the in-phase voltage level and the quadrature voltage level varying in accordance with the variation in frequency of the second downstream signal;

(g) tuning the second downstream signal between the first and the second downstream frequencies to produce a plurality of in-phase voltage levels and a plurality of quadrature voltage levels;

(h) determining a time delay associated with the source of common path distortion from the plurality of in-phase voltage levels and the plurality of quadrature voltage levels; and

(i) determining the distance to the source of common path distortion from the time delay.

15. A method according to claim 14, wherein step (g) includes producing a generally circular voltage pattern with the plurality of in-phase voltage levels and the plurality of quadrature voltage levels, and wherein step (h) includes determining the time delay from the reciprocal of the frequency change required to trace out the generally circular voltage pattern.

16. A method according to claim 14, further comprising the step of determining a complex frequency response from the plurality of in-phase voltage levels and the plurality of quadrature voltage levels, and wherein step (h) includes determining an impulse response from the complex frequency response and obtaining the time delay from the impulse response.

17. A method of ranging a distance to a source of common path distortion in a two-way cable system that has a downstream signal path and an upstream signal path, said method comprising the steps of:

(a) generating a first downstream signal having a fixed frequency, for transmission in the downstream signal path of the cable system;

(b) generating a second downstream signal having a tunable frequency varying between first and second downstream frequencies, for transmission in the downstream signal path of the cable system;

(c) transmitting the first and the second downstream signals in the downstream signal path of the cable system;

(d) receiving an upstream signal from the upstream signal path of the cable system, the upstream signal being created by the source of common path distortion by a mixing action of the first downstream signal with the second downstream signal, the upstream signal varying in frequency between first and second upstream frequencies in accordance with a variation in frequency between first and second downstream frequencies, respectively, of the second downstream signal;

(e) generating a mixing signal varying in frequency between the first and the second upstream frequencies in accordance with the variation in frequency between the first and the second downstream frequencies, respectively, of the second downstream signal;

(f) mixing the upstream signal with the mixing signal to produce a voltage level that varies generally sinusoidally in accordance with the variation in frequency of the second downstream signal;

(g) tuning the second downstream signal between the first and the second downstream frequencies, to produce a generally sinusoidal voltage pattern in accordance with step (f);

(h) determining a time delay associated with the source of common path distortion from the generally sinusoidal voltage pattern; and

(i) determining the distance to the source of common path distortion from the time delay.

18. A method according to claim 17, wherein the frequency range of the downstream signal path of the cable system includes the FM radio band,

and wherein step (a) includes generating the first downstream signal with a fixed frequency within the FM radio band,

and wherein step (b) includes generating the second downstream signal having a tunable frequency range within the FM radio band.