Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – With auxiliary means to condition stimulus/response signals
Patent
1993-09-27
2000-05-16
Ballato, Josie
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
With auxiliary means to condition stimulus/response signals
324615, 702110, G01R 2728
Patent
active
060642122
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for determining the transmission characteristics of an electric line in an ISDN system, in which test signal is evaluated by being scanned during a time interval corresponding to the period of the test signal and being subjected to a Fourier transformation to obtain a spectral signal.
In a known method of this type (DE 2,849,119 C2), use is made as test signal of a test pulse which is derived from the superposition of a sequence of harmonic oscillations. In this case, the amplitude values and the phase angles of the individual frequency components are selected with regard to a low crest factor by means of a memory in a signal generator. Given skilful selection, a test pulse with a crest factor of 4.03 can be achieved. The test pulse modified by the device under test is scanned as received signal during a period; the scan values are stored in digital form. Subsequently, a fast Fourier transformation is performed, by means of which it is possible to calculate the amplitude and phase for each harmonic of the test pulse. Using the corresponding stored magnitudes of the non-corrupted test pulses, it is then possible to determine the attenuation or the attenuation distortion of the device under test.
It is the object of the invention to specify a method for determining the transmission characteristics of an electric line in an ISDN system which can be carried out with relatively little cost with respect to the generation of the test signal and with respect to the evaluation of the received signal, and which operates using a test signal having the crest factor of one. In order to determine the transmission characteristics of electric lines in an ISDN (Integrated Services Digital Network) system, there is, specifically, the requirement to operate using a test signal having as far as possible the crest factor of one.
In order to achieve the specified object, in the method, specified at the beginning, according to the invention it is provided that ISDN system use is made as test signal of a binary, bipolar random number sequence signal having the crest factor of one, and that obtain an output signal which represents a measure of the transmission characteristics of the line, the reference spectrum being obtained from the time-inverse test signal.
An advantage of the method according to the invention consists in the use of a binary, bipolar random number sequence signal, because such a signal has the crest factor of one and can be directly generated, for example, using feedback shift registers. Moreover, the parameters of such a signal can easily be held stationary. A further advantage of the method according to the invention consists in that its realization is performed in the image region of the Fourier transformation in which it is possible to implement the mathematical folding operation by the multiplication of two spectra, which is relatively simple to carry out.
It is true that GB Patent 1,160,271 discloses a method for determining a pulse response of an electrical system, in which use is made as test signal of a binary, bipolar random number sequence signal having a crest factor of one, but in this case it is a question in the electrical system of a servo-system, and after traversing the servo-system the test signal is cross-correlated with delayed random number sequence signals obtained from the test signal in each case by means of delays of different length.
Furthermore, in the digital processing of measuring signals it is known in principle (cf., for example, "Technisches Messen tm" ("Technical measurement tm"), volume 54, issue 1/1987, pages 20 to 25, as well as issue 2/1987, pages 66 to 74, "IEEE Transactions on Instrumentation and Measurement", vol. IM-32, No. 3, September 1983, pages 447 to 450 and H. Kaden "Impulse und Schaltvorgange in der Nachrichtentechnik" ("Pulses and switching operations in telecommunications engineering") 1957, pages 261 to 269) to scan a signal during a time interval corresponding to the period of another signal and to subject it to a Fourier tr
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Arweiler Hans Werner
Wolf Andreas
Ballato Josie
Lenihan Thomas F.
Mayer Richard L.
Solis Jose M.
Tektronix Inc.
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