Method for measuring spectral energy interference in a cable transmission system

• US 5,939,887 A
• Filed: 09/05/1997
• Issued: 08/17/1999
• Est. Priority Date: 09/05/1997
• Status: Expired due to Term

• Current Assignee: Tektronix Incorporated (Fortive Corp.)
• Original Assignee: Tektronix Incorporated (Fortive Corp.)
• Inventors: Schmidt, David W., Harris, Gerald S.
• Primary Examiner(s): Do, Diep N.
• Application Number:
  US08/924,753
• Time in Patent Office: 711 Days
• Field of Search: 324/612, 324/613, 324/620, 324/628, 324/76.19, 324/76.23, 324/76.26, 324/76.27, 455/63, 455/67.2, 455/67.3, 455/202, 455/296, 455/501, 348/6, 348/17, 348/21, 348/180, 348/193, 348/470, 379/6, 379/414, 379/416, 333/12
• US Class Current: 324/628
• CPC Class Codes: H04B 3/46 Monitoring; Testing
• CPC Class Codes: H04L 1/24 Testing correct operation

Abstract

A method for measuring interference in a cable transmission system includes the step of establishing a spectrum frequency measurement window having start and stop frequencies and an amplitude threshold. Data is acquired over the window representative of the spectral energy of the cable transmission system within the window and the data is compared against the threshold value. If the data falls below the threshold value, indicating the absence of a carrier signal within the window, a display is generated characterizing the interference over the window. Additional measurement windows may be established having different start and stop frequencies and thresholds for measuring different portions of the cable transmission system frequency spectrum.

Claims

1. A method for measuring spectral energy in a cable transmission system having a headend for transmitting data to transceivers in a forward path and transmitting data from the transceivers to the headend in a reverse path over a distribution system comprising the steps of:

1) establishing a spectral frequency measurement window having a start frequency and a stop frequency and an amplitude threshold value;

2) acquiring data over the spectral frequency measurement window representative of the magnitude of the spectral energy in the cable transmission system over the window;

3) comparing the acquired data to the amplitude threshold value; and

4) generating a display characterizing interference in the cable transmission system over the spectral frequency measurement window when the acquired data is less than the amplitude threshold value.

2. The method for measuring spectral energy in a cable transmission system as recited in claim 1 wherein the acquiring step further comprises the steps of:

1) digitizing the spectral energy over the spectral frequency measurement window for producing digital data values representing the magnitude of the spectral energy over the spectral frequency measurement window; and

2) storing the digital data values in a digital memory.

3. The method for measuring spectral energy in a cable transmission system as recited in claim 2 wherein the generating step further comprises the step of displaying the interference data in the form of a spectral trace on a display device.

4. The method for measuring spectral energy in a cable transmission system as recited in claim 3 wherein the generating step further comprises the step of displaying the start and stop frequencies and the amplitude threshold value of the spectral frequency measurement window with the spectral trace on a display device.

5. The method for measuring spectral energy in a cable transmission system as recited in claim 3 wherein the generating step further comprises the step of displaying the start and stop frequencies and the amplitude threshold value of the spectral frequency measurement window as cursors associated with the spectral trace on the display device.

6. The method for measuring spectral energy in a cable transmission system as recited in claim 2 wherein the generating step further comprises the step of calculating a delta value representative of the difference between the threshold value and the interference data point having the greatest magnitude.

7. The method for measuring spectral energy in a cable transmission system as recited in claim 6 wherein the generating step further comprises the step of displaying the delta value and the frequency corresponding to the interference data point of the delta value.

8. The method for measuring spectral energy in a cable transmission system as recited in claim 6 wherein the generating step further comprises the step of displaying the start and stop frequencies and the amplitude threshold value of the spectral frequency measurement window, the delta value, the frequency corresponding to the data point of the delta value, and the interference data in the form of a spectral trace on a display device.

9. The method for measuring spectral energy in a cable transmission system as recited in claim 8 wherein the generating step further comprises the step of displaying the start and stop frequencies and the amplitude threshold value of the spectral frequency measurement window as cursors associated with the spectral trace on the display device.

10. The method for measuring spectral energy in a cable transmission system as recited in claim 1 further comprising the step of repeating steps 1 through 4 for an additional spectral frequency measurement window.

11. The method for measuring spectral energy in a cable transmission system as recited in claim 10 wherein the acquiring step further comprises the steps of:

1) digitizing the spectral energy over the additional spectral frequency measurement window for producing digital data values representing the magnitude of the spectral energy over the additional spectral frequency measurement window; and

2) storing the digital data values in a digital memory.

12. The method for measuring spectral energy in a cable transmission system as recited in claim 11 wherein the generating step further comprises the step of displaying the interference data of the additional spectral frequency measurement window in the form of a spectral trace on a display device.

13. The method for measuring spectral energy in a cable transmission system as recited in claim 12 wherein the generating step further comprises the step of displaying the start and stop frequencies and the amplitude threshold value of the additional spectral frequency measurement window with the spectral trace on a display device.

14. The method for measuring spectral energy in a cable transmission system as recited in claim 12 wherein the generating step further comprises the step of displaying the start and stop frequencies and the amplitude threshold value of the additional spectral frequency measurement window as cursors associated with the spectral trace on the display device.

15. The method for measuring spectral energy in a cable transmission system as recited in claim 11 wherein the generating step further comprises the step of calculating a delta value representative of the difference between the threshold value of the additional spectral frequency measurement window and the interference data point having the greatest magnitude.

16. The method for measuring spectral energy in a cable transmission system as recited in claim 15 wherein the generating step further comprises the step of displaying the delta value and the frequency corresponding to the interference data point of the delta value of the additional spectral frequency measurement window.

17. The method for measuring spectral energy in a cable transmission system as recited in claim 15 wherein the generating step further comprises the step of displaying the start and stop frequencies and the amplitude threshold value of the additional spectral frequency measurement window, the delta value, the frequency corresponding to the data point of the delta value, and the interference data of the additional spectral frequency measurement window in the form of a spectral trace on a display device.

18. The method for measuring spectral energy in a cable transmission system as recited in claim 17 wherein the generating step further comprises the step of displaying the start and stop frequencies and the amplitude threshold value of the additional spectral frequency measurement window as cursors associated with the spectral trace on the display device.

19. The method for measuring spectral energy in a cable transmission system as recited in claim 1 wherein the establishing step further comprises the step of establishing sub-spectral frequency measurement windows within the spectral frequency measurement window with each sub-window having a start frequency and a stop frequency and an amplitude threshold value.

20. The method for measuring spectral energy in a cable transmission system as recited in claim 19 wherein the acquiring step further comprises the steps of:

1) digitizing the spectral energy over the spectral frequency measurement window for producing digital data values representing the magnitude of the spectral energy over the spectral frequency measurement window; and

2) storing the digital data values in a digital memory.

21. The method for measuring spectral energy in a cable transmission system as recited in claim 20 wherein the comparing step further comprises the step of comparing the acquired data for each of the sub-windows to the amplitude threshold value for the respective sub-window.

22. The method for measuring spectral energy in a cable transmission system as recited in claim 21 wherein the generating step further comprises the step of generating a display characterizing the interference in the cable transmission system over the spectral frequency measurement window when the interference data for any of the sub-windows is less than the amplitude threshold value for that sub-window.

23. The method for measuring spectral energy in a cable transmission system as recited in claim 22 wherein the generating step further comprises the step of displaying the interference data in the form of a spectral trace on a display device.

24. The method for measuring spectral energy in a cable transmission system as recited in claim 23 wherein the generating step further comprises the step of displaying the start and stop frequencies and the amplitude threshold values of the sub-windows with the spectral trace of the interference data on a display device.

25. The method for measuring spectral energy in a cable transmission system as recited in claim 23 wherein the generating step further comprises the step of displaying the start and stop frequencies and the amplitude threshold values of the sub-windows as cursors associated with the spectral trace on the display device.

26. The method for measuring spectral energy in a cable transmission system as recited in claim 22 wherein the generating step further comprises the step of calculating delta values representative of the difference between the interference data point having the greatest magnitude in each sub-window and the threshold value for that sub-window.

27. The method for measuring spectral energy in a cable transmission system as recited in claim 26 wherein the generating step further comprises the step of displaying the delta values and the frequencies corresponding to the interference data points of the delta values for each sub-window.

28. The method for measuring spectral energy in a cable transmission system as recited in claim 26 wherein the generating step further comprises the step of displaying the start and stop frequencies and the amplitude threshold values of each sub-window, the delta values, the frequencies corresponding to the data points of the delta values for each sub-window, and the interference data in the form of a spectral trace on a display device.

29. The method for measuring spectral energy in a cable transmission system as recited in claim 28 wherein the generating step further comprises the step of displaying the start and stop frequencies and the amplitude threshold value of the spectral frequency measurement window as cursors associated with the spectral trace on the display device.