Method for measuring the attenuation in digital transmission lines

A method for measuring the attenuation in digital transmission lines between a switching center and a subscriber station, which comprises

• sending a first pulse of a known frequency spectrum in the shape of individual sine-shaped signals whose frequency has previously been determined from the frequency spectrum of the first pulse from the switching center to a transmission line;
• selecting a pulse from the multitude of the reflections received by the switching center in the time domain which was caused by the total reflection at the end of the line of a certain subscriber station, whereby the reflections in the time domain are determined by inverse Fourier transformation of the frequency spectrum of these reflections;
• determining the frequency spectrum of the selected pulse and determining the attenuation of the transmission line depending on the frequency, from the frequency spectrum of the first pulse and the selected received pulse, wherein
• a clock-pulse signal of a frequency F0 is generated by using a vectorial network analyzer comprising an oscillator;
• generating a signal of a frequency F1 by a first synthesizer from the frequency F0, said generated signal being fed to two identically constructed directional couplers, with a first directional coupler being used to generate a reference signal and with the measuring gate of said first directional coupler being open or short circuited, and the transmission line to be measured being connected to a second directional coupler;
• feeding the reflected signals of one of the directional couplers to one of two mixers on a first input;
• generating a signal of the frequency F2 by a second synthesizer from the frequency F0, which signal is fed to second inputs of the two mixers;
• feeding output signals of the two mixers to two low passes at a frequency F3 resulting from the frequencies F1 and F2, with each of said low passes being switched in line with A/D converter;
• generating a clock-pulse signal of the frequency F4 by a frequency divider which shares the clock-pulse signal with the frequency F0, which signal is used as a sampling cycle for the A/D converters;
• and providing a computer which receives the signals of the A/D converters and adjusts the synthesizers and determines the attenuation from the relationship between the signals supplied by the A/D converter allocated to the transmission line, and the signals of the other A/D converter, whereby, starting from the frequency F0, a base frequency F_base is derived from F0 by binary division;
• selecting the frequency F3 in such a way that it results as a power of two from F_base;
• using only integral multiples of F_base as frequencies F1 and F2;
• generating the frequency F4 by binary division from F0 with F4=4·F3;
• and
• sampling the signal of the frequency F3 with the relationship m=F4/F_base or a multiple of it formed by a power of two.