Detection of bridge tap using frequency domain analysis

• US 6,177,801 B1
• Filed: 04/21/1999
• Issued: 01/23/2001
• Est. Priority Date: 04/21/1999
• Status: Expired due to Fees

• Current Assignee: Sunrise Telecom Incorporated
• Original Assignee: Sunrise Telecom Incorporated
• Inventors: Chong, Raymond L.
• Primary Examiner(s): Metjahic, Safet
• Assistant Examiner(s): Deb, Anjan K
• Application Number:
  US09/295,857
• Time in Patent Office: 643 Days
• Field of Search: 324/520, 324/533, 324/527, 324/532, 324/537, 324/535, 324/543
• US Class Current: 324/520
• CPC Class Codes: G01R 31/11 using pulse reflection methods
• CPC Class Codes: G01R 31/50 Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections testing of sparking plugs H01T13/58
• CPC Class Codes: H04B 3/46 Monitoring; Testing
• CPC Class Codes: H04M 3/306 for frequencies above the voice frequency, e.g. xDSL line qualification test methods, test equipment and test arrangements for subscriber lines using xDSL modems H04M3/304; systems modifying transmission characteristics according to link quality H04L1/0001; monitoring and/or testing of line transmission systems H04B3/46

Abstract

A method for detecting the presence of a bridge tap and other types of fault in a transmission line. Initially, test signals of predetermined frequencies are transmitted into a transmitting end of the transmission line. The test signals are received at a receiving end of the transmission line and the amplitudes of the received signal are measured. A frequency response of the transmission line is computed based on the measured amplitudes. The frequency response is then analyzed for the presence of a frequency-domain signature that corresponds to one of the detectable types of fault. The presence of a bridge tap or another type of fault is identified based on the detected frequency-domain signature. The frequency-domain signature associated with a bridge tap can comprise a set of one or more attenuation dips in the frequency response, with each attenuation dip corresponding to a local minima in the frequency response. The length of the bridge tap can be estimated based on a fundamental frequency of the set of harmonically related attenuation dips. Also, the location of the bridge tap in the transmission line can be estimated by performing a time domain reflectometer (TDR) test.

Claims

1. A method for detecting presence of a bridge tap in a transmission line comprising:

transmitting test signals of predetermined frequencies into a transmitting end of the transmission line;

measuring amplitudes of the test signals at a receiving end of the transmission line;

computing a frequency response of the transmission line based on the measured amplitudes;

detecting the presence of a frequency-domain signature in the frequency response of the transmission line; and

identifying the presence of the bridge tap fault based on the identified frequency-domain signature.

2. The method of claim 1 wherein the transmitting and receiving ends are opposite ends of the transmission line.

3. The method of claim 1 further comprising:

displaying the frequency response as a graphical plot.

4. The method of claim 1 further comprising:

executing a time domain reflectometer (TDR) test; and

determining a location of the identified bridge tap based on results from the TDR test.

5. The method of claim 1 wherein the frequency-domain signature associated with a bridge tap comprises a set of one or more attenuation dips in the frequency response, wherein each attenuation dip is a local minina in the frequency response.

6. The method of claim 5 wherein the attenuation dips are harmonically related.

7. The method of claim 6 further comprising:

computing a length of the bridge tap based on a frequency of a first attenuation dip in the set of harmonically related attenuation dips.

8. The method of claim 7 wherein the computing is performed in accordance with an equation

9. The method of claim 8 wherein the length of the bridge tap (l), for an open circuit termination, is estimated as:

$l\cong <br><br>\frac{v_P·<br><br>c}{4<br><br>f_1},$

wherein f₁ is the frequency of the first attenuation dip in the set of harmonically related attenuation dips.

10. The method of claim 8 wherein the length of the bridge tap (l), for a short circuit termination, is estimated as:

$l\cong <br><br>\frac{v_P·<br><br>c}{2<br><br>f_1},$

wherein f₁ is the frequency of the first attenuation dip in the set of harmonically related attenuation dips.

11. The method of claim 8 wherein v_P is derived from empirical measurement.

12. The method of claim 8 wherein v_P is set to a default value within a range of 0.4 to 0.8.

13. The method of claim 12 wherein v_P is set to a default value of approximately 0.64.

14. A method for detecting presence of a bridge tap in a transmission line comprising:

transmitting test signals of predetermined frequencies into a transmitting end of the transmission line;

measuring amplitudes of the test signals at a receiving end of the transmission line, wherein the transmitting and receiving ends are opposite ends of the transmission line;

computing a frequency response of the transmission line based on the measured amplitudes;

detecting the presence of a frequency-domain signature in the frequency response of the transmission line, wherein the frequency-domain signature comprises a set of one or more harmonically related attenuation dips in the frequency response, wherein each attenuation dip is a local minima in the frequency response;

identifying the presence of the bridge tap based on the identified frequency-domain signature;

executing a time domain reflectometer (TDR) test; and

determining a location of the bridge tap based on results from the TDR test.