Method and test unit for far end crosstalk measurements

Details Method and test unit for far end crosstalk measurements Method and test unit for far end crosstalk measurements

1999-07-20

2001-07-10

Metjahic, Safet (Department: 2851)

Electricity: measuring and testing

Impedance, admittance or other quantities representative of...

Parameter related to the reproduction or fidelity of a...

C324S539000

Reexamination Certificate

active

06259258

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the measurement of far end crosstalk in a multi-pair cable. In particular, the invention relates to a method and a test unit for providing phase coherent test signals at either end of a cable under test.
BACKGROUND OF THE ART
Crosstalk is the unwanted coupling of signals from one pair to another along a multi-pair cable. When crosstalk is measured at the same end of the cable where the crosstalk originates, the measurement technique is called near end crosstalk (NEXT). Twisted pair LAN technologies, such as 10BASE-T, 100BASE-T, and Token Ring are primarily vulnerable to cable crosstalk problems in a manner that is best tested by measuring the NEXT of the installed cable.
When crosstalk is measured at the end of the cable opposite from where the crosstalk originates, the measurement technique is called far end crosstalk (FEXT). FEXT is measured by applying a test signal to a wire pair at a far end of the cable and measuring the disturbance on the other wire pairs in the cable at the other or near end. It is relevant to specify the FEXT performance of cabling for network technologies, such as the new 1000BASE-T specification, that transmit simultaneously on multiple wire pairs in the same direction.
While it is easy to measure the FEXT performance of an installed multi-pair cable, it is difficult to specify certification limits for such measurements, since FEXT varies with the cable length. The equal level far end crosstalk (ELFEXT) measurement technique was developed as a practical alternative for field certification. Generally, ELFEXT equals FEXT minus attenuation caused by the cable. ELFEXT measurements compensate for the effect of varying cable length so that all installed cable can be certified to the same limit.
Residual crosstalk is any signal that is due to the test instrument itself. Residual crosstalk error must be taken into account in crosstalk measurement analysis.
With vector measurements, residual crosstalk errors can be mathematically cancelled. When an error term cancellation in a vector measurement is employed, the test instruments at either end of the cable need to generate test signals that are phase coherent with one another.
Accordingly there is a need for a method of generating phase coherent test signals at either end of the cable. There is also a need for a test instrument that can be used at either end of the cable and that is capable of producing a test signal that is coherent with another test signal generated at the other end of the cable.
SUMMARY OF THE INVENTION
The method of the invention is used in a system that conducts far end crosstalk measurements of a multi-pair cable that is under test. The system employs a near end test unit and a far end test unit, arranged at opposite ends of the cable. The near and far end test units each have a signal generator.
According to the method of the invention, a first test signal is generated with the far end signal generator and a second test signal is generated with the near end signal generator. The phases of the first and second test signals are synchronized to produce phase coherency of the two signals. The first test signal is transmitted from the far end. A FEXT measurement is performed using the first and second test signals and a crosstalk signal induced by the first test signal in one or more wire pairs of the cable.
In particular, synchronization is accomplished by generating a reference signal with the far end generator in phase synchronization with the first test signal. The reference signal is transmitted from the far end of the cable. At the near end, the near end signal generator is controlled, responsive to the received reference signal, to produce the second test signal in phase coherency with the first test signal.
A test unit in accordance with the invention includes a signal generator that is capable of operating as far end or a near end signal generator to perform the functions of the method described above.


REFERENCES:
patent: 4970466 (1990-11-01), Bolles et al.
patent: 5530367 (1996-06-01), Bottman
patent: 5532603 (1996-07-01), Bottman
patent: 5539321 (1996-07-01), Sciacero et al.
patent: 5698985 (1997-12-01), Bottman

Affiliated with

Also associated with

Rating

Method and test unit for far end crosstalk measurements does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method and test unit for far end crosstalk measurements, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and test unit for far end crosstalk measurements will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2562018