Method for testing local telephone cable frequency response

Abstract

The present invention relates to a testing local cable frequency response method. It contains 1, obtaining cable narrowband parameter by digital multimeter, judging whether cable having narrowband fault, if having then reporting fault, otherwise executing step 2; 2, according to testing obtained local cable narrowband parameter judging cable fitting adopting digital multimeter testing or time domain reflection testing to obtain cable frequency response, and according to judging result adopting relevant testing to obtain frequency response. The present invention adopts two test methods combined mode to test local cable frequency response, to solve test result declinational problem due to cable earth capacitance inconsistency.

Description

technical field [0001] The invention relates to the field of communication cable testing, in particular to a method for testing the frequency response of local telephone cables. Background technique [0002] In the field of telecommunication services, operators provide users with both broadband telecommunication services and narrowband telecommunication services through local telephone cables (usually twisted pairs), such as ADSL over POTS (ADSL is added to ordinary telephones), ADSL over ISDN (ADSL is added to ISDN ), VDSL over POTS (ordinary telephone plus VDSL), VDSL over ISDN (ISDN plus VDSL) and other services, such applications have been quite common at home and abroad. (hereinafter referred to as XDSL for ADSL and VDSL). [0003] XDSL signals and POTS / ISDN signals coexist in a user's outside line. The splitter in the broadband access equipment at the central office side separates the wide and narrow services and sends them to the broadband service board and narrowban...

AI Technical Summary

Problems solved by technology

The method of using the time domain reflection method to test the frequency response has the following disadvantages: 1. Because the tested reflected pulse has to go through twice the cable length to return to the data collector at the local end, when the cable is longer, the measured reflected pulse The amplitude will become very small, and the test becomes very difficult

For example, if the cable to be tested is a cable with a length of 4 kilometers and a line diameter of 0.4 mm, the pulse with a main frequency component of 300KHz is attenuated by 14DB per kilometer, and the pulse is attenuated by 56DB when it is transmitted from the cable source to the cable terminal. After total reflection, it is transmitted to the source end, and it is attenuated by 56DB, and the total attenuation is 112DB; considering the existence of noise in the test environment, it is difficult to test such a small-amplitude pulse accurately

2. When the cable terminal is in a matching state, the frequency response test method based on the principle of time domain reflection is not feasible

The use of a digital multimeter test module has the following disadvantages: 1. The capacitance of the cable core wire to ground varies from more than 50 to 60 nanofarads (maximum 60 nanofarads) per kilometer, with a maximum deviation of 20%, resulting in a corresponding test of the cable frequency. The results also have a maximum 20% deviation

2. When the user side of the cable is connected to the terminal, the capacitance of the terminal varies with the type of the terminal, which affects the capacitance value between the A line and the B line, resulting in inaccurate test results

It is very troublesome to solve Cag, Cbg and Cab through the above three equations, and often there is no solution due to the existence of test errors

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