Apparatus for decoupling a radio-frequency signal transmitted on a data transmission line

An apparatus for decoupling a radio-frequency signal transmitted on a data transmission line having a first line element and a second line element, or for decoupling interference voltages includes: a tapping module, connected to the first and second line elements at a first tapping location of the data transmission line, for decoupling the radio-frequency signal or interference voltages; a current probe module, coupled to the first line element at a second tapping location of the data transmission line; and an output capable of being matched to different input impedances of a device connected to the output.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a national stage entry under 35 U.S.C. §371 of International Application No. PCT/EP2011/001407, filed Mar. 22, 2011, and claims priority to European Patent Application No. EP 10003252.3, filed Mar. 26, 2010, and European Patent Application No. EP 10008666.9, filed Aug. 19, 2010. The International Application was published in German on Sep. 29, 2011 as WO 2011/116928.

FIELD

The present invention relates to an apparatus for decoupling a radio-frequency signal transmitted on a data transmission line or for decoupling interference voltages, in particular for the purpose of carrying out a measurement on the permanently installed data transmission line.

BACKGROUND

Data transmission lines are installed in their millions nowadays, for example for the purpose of supplying private households or companies with comparatively broadband data connections. By way of example, currently approximately 20 million DSL connections (Digital Subscriber Line connections), in particular ADSL connections (Asymmetric Digital Subscriber Line connections) or VDSL connections (Very High Bitrate Digital Subscriber Line connections), are currently set up in the copper conductor pair network of Deutsche Telekom AG in Germany. Depending on the operating state and configuration of these systems, the power spectral densities (so-called PSD spectra, Power Spectral Density spectra) that can be measured on individual data transmission lines of such data transmission systems can deviate considerably from the power spectral density striven for.

Hitherto, the measurement of individual data transmission lines of such data transmission systems has been able to be realized only with various disadvantages being accepted. Said disadvantages include, inter alia, comparatively low measurement accuracy particularly when measuring the power spectral density, and often the necessity that, for carrying out the measurement of a predefined data transmission line, the latter has to be isolated, i.e. interrupted.

SUMMARY

In an embodiment, the present invention provides an apparatus for decoupling a radio-frequency signal transmitted on a data transmission line having a first line element and a second line element, or for decoupling interference voltages. The apparatus includes: a tapping module, connected to the first and second line elements at a first tapping location of the data transmission line, for decoupling the radio-frequency signal or interference voltages; a current probe module, coupled to the first line element at a second tapping location of the data transmission line; and an output capable of being matched to different input impedances of a device connected to the output.

DETAILED DESCRIPTION

In an embodiment, the present invention provides an apparatus for decoupling a radio-frequency signal transmitted on a data transmission line or for decoupling interference voltages, which avoids or at least reduces the disadvantages of the prior art and which is constructed and can be produced simply and cost-effectively and can be used in a simple and efficient manner in practical testing.

In an embodiment, the present invention provides an apparatus for decoupling a radio-frequency signal transmitted on a data transmission line having a first line element and a second line element, wherein the apparatus comprises a tapping module and a current probe module, wherein a connection of the tapping module to the first and second line elements at a first tapping location of the data transmission line is provided for the purpose of decoupling the radio-frequency signal, and wherein a coupling of the current probe module to the first line element at a second tapping location of the data transmission line is provided for the purpose of decoupling the radio-frequency signal. In a further embodiment, the present invention provides an apparatus for decoupling a radio-frequency signal transmitted on a data transmission line (50) having a first line element (51) and a second line element (52), or for decoupling interference voltages, wherein the apparatus (10) comprises a tapping module (20) and a current probe module (30), wherein a connection of the tapping module (20) to the first and second line elements (51,52) at a first tapping location (61) of the data transmission line (50) is provided for the purpose of decoupling the radio-frequency signal and interference voltages, and wherein

a coupling of the current probe module (30) to the first line element (51) at a second tapping location (62) of the data transmission line (50) is provided in the case of decoupling the radio-frequency signal, and

a coupling of the current probe module (30) to the first and second line elements (51,52) at a second tapping location (62) of the data transmission line (50) is provided in the case of decoupling the interference voltages.

The apparatus according to the invention has the advantage that, in contrast to a customary directional coupler of closed design, an uninterruptable measurement of the data transmission line is possible. This firstly has the advantage that, for carrying out the measurement, the data transmission line to be measured does not have to be interrupted and subsequently reconnected, such that a different (matching) configuration (not measured) possibly results after the measurement has been carried out. Furthermore, this has the advantage that the measure of interruption and reconnection is not required, such that the measurement first of all takes place more accurately (because error sources occurring after the measurement, caused for instance by the reconnection, are avoided) and secondly is simpler, faster and possible with less expenditure of work time. According to the invention, the apparatus can be used both for measuring a radio-frequency signal and for measuring interference voltages (or irregular interference signals) on the data transmission line. In this case, the apparatus is operated in a so-called differential mode for the purpose of decoupling the radio-frequency signal and in a so-called common mode for the purpose of decoupling the interference voltages. The two operating modes or tapping modes substantially differ only in the different handling or the different tapping. The radio-frequency signals (i.e. the useful signals, for example xDSL signals, to be transmitted on the data transmission line generate, on the data transmission line embodied as a conductor pair, a differential-mode voltage or differential voltage between the first line element and the second line element. For the measurement of these radio-frequency signals, the apparatus according to the invention is used in differential-mode operation. With the aid of this measurement, the xDSL transmission power coupled into a cable is primarily intended to be measured as exactly as possible. In one preferred embodiment, on account of the directional coupler effect, the signal direction of the xDSL signal can be determined with the aid of a switch. On account of diverse causes, undesirable interference voltages are also coupled via various interference paths into telecommunication cables generally as common mode. The interference voltage is then between the data transmission line (generally a conductor pair or a copper conductor pair) and ground or the cable sheath. The interference potential on both line elements with respect to ground of the data transmission line is thus identical; for the common mode, the data transmission line can be imagined as a single line (or the two line elements as a single line). Common-mode operation is used for the measurement of these interference variables or interference voltages. In the preferred embodiment with a switch, the fundamentally unknown signal direction of the interference signal is primarily intended to be determined in order to localize the interference transmitter. Although the apparatus in common-mode operation, too, can ensure measurement accuracies similar in magnitude to those in differential-mode operation, the absolute measurement accuracy does not play a crucial part in locating the interference source.

The apparatus according to the invention is used as a directional coupler and is connected to the data transmission line for the purpose of decoupling the radio-frequency signal transmitted on the generally permanently installed data transmission line, or for the purpose of decoupling interference voltages, in which case, however, no change whatsoever is made to the predefined configuration of the installation of the data transmission owing to the measurement being carried out. For this purpose, the apparatus according to the invention comprises two modules or measuring modules, which are preferably coordinated with one another and together realize the decoupling of the radio-frequency signal transmitted on the signal transmission line to be measured. The present invention is illustrated primarily on the basis of the example of decoupling a radio-frequency signal or interference voltages on a data transmission line having a first line element and a second line element, in particular taking as a basis the example of a copper wire pair (copper conductor pair) as the data transmission line. However, the invention can also be applied to other types of data transmission line, for example comprising more than two line elements and/or comprising other line materials.

The two modules or measuring modules in the apparatus according to the invention are a tapping module and a current probe module. The tapping module serves for tapping, i.e. voltage tapping,

in the case of decoupling the radio-frequency signal (differential-mode operation) between the first line element and the second line element of the data transmission line and

in the case of decoupling the interference voltages (common-mode operation) between the line elements of the data transmission line, on the one hand, and ground, on the other hand. This tapping is effected at a first tapping location along the extent of the data transmission line. The current probe module serves for coupling at a second tapping location along the extent of the data transmission line, to be precise
by coupling the current probe module to the first line element of the data transmission line in the case of decoupling the radio-frequency signal, and
by coupling the current probe module to the first and second line elements of the data transmission line in the case of decoupling interference voltages.

The apparatus serves, in particular, for carrying out measurements of the power spectral density of the data transmission line or carrying out measurements for locating interference sources. In this case, it is provided, in particular, that a further device for fully carrying out such a measurement is connected to an output of the apparatus according to the invention. In particular, a so-called spectrum analyzer, which first performs the actual measurement of the power spectral density, is appropriate as such a further device. However, the apparatus according to the invention makes the measurement signal available to such a spectrum analyzer, i.e. the measurement accuracy of the measurement carried out is sensitively dependent on the apparatus according to the invention, which, in the case of such a measurement set-up, serves as a measuring head for the spectrum analyzer and is therefore also designated hereinafter as applied power measuring head.

According to the invention, it is preferred for the current probe module to have a split toroidal core magnet. It is thereby possible in an advantageous manner to perform a particularly simple and accurate measurement of the current flow through the first line element of the data transmission line.

According to the invention, it is furthermore also preferred that in the case of decoupling the interference voltages, a coupling of the current probe module (30) to the first and second line elements (51,52) is provided in such a way that the current probe module (30) embraces the first and second line elements (51,52) in the same sense.

It is thereby advantageously possible according to the invention to perform a simple measurement of the interference voltages by means of a simple tapping or by means of a simple coupling of the current probe module to the first and second line elements.

According to the invention, it is furthermore preferred for the tapping module to be embodied as a sensing head having a first tapping element and a second tapping element. It is thereby possible in an advantageous manner for the measurement to be effected rapidly and simply.

It is furthermore preferred if the apparatus is configured in such a way that the first and second tapping locations are at a distance from one another of 2 cm to 200 cm, preferably of 5 cm to 50 cm, particularly preferably of 8 cm to 15 cm, especially preferably 10 cm. This distance between the first tapping location and the second tapping location refers, in particular, to the distance between the tapping locations along the extent of the data transmission line.

According to the invention, it is furthermore also preferred for the apparatus to comprise a changeover switch, wherein the changeover switch effects a circuitry interchange of the tapping elements of the tapping module. This means that in the case of an electrically conductive connection of the first tapping element (of the tapping module) to the first line element and an electrically conductive connection of the second tapping element to the second line element (in the case of decoupling the radio-frequency signal, i.e. operation of the apparatus in differential-mode operation), a switch-over of the changeover switch brings about a connection configuration of the apparatus to the line elements of the data transmission line in such a manner as if the first tapping element had an electrically conductive connection to the second line element and the second tapping element had an electrically conductive connection to the first line element. Correspondingly, in the case of an electrically conductive connection of the first tapping element (of the tapping module) to the first and second line elements and an electrically conductive connection of the second tapping element to ground (of the data transmission line) (in the case of decoupling interference voltages, i.e. operation of the apparatus in common-mode operation), a switch-over of the changeover switch brings about a connection configuration of the apparatus to the line elements of the data transmission line in such a manner as if the first tapping element had an electrically conductive connection to ground and the second tapping element had an electrically conductive connection to the first and second line elements. As a result, in both cases or both operating modes, according to the invention firstly it is possible particularly simply and rapidly to perform a good coordination or matching of the apparatus to the impedance relations of the data transmission line to be measured, and secondly it is thereby possible, when carrying out the measurement, to minimize the outlay to the effect that it is not necessary to make a change to the tapping of the tapping module on the data transmission line or a change in the coupling of the current probe module on account of incorrect polarity, rather it is merely necessary to operate the changeover switch. This accelerates the performance of the measurement and furthermore improves the measurement accuracy, since with the same tapping configuration (i.e. with the possibility of good matching to the impedance relations) it is also possible to carry out the measurement without necessitating an interchange of the tapping on the first and second line elements.

According to the invention, it is furthermore likewise preferably provided that the apparatus has a decoupling attenuation of 40 dB+/−0.1 dB from 30 kHz to 30 MHz. It is thereby preferably possible according to the invention that a connected spectrum analyzer is not overdriven. On account of the high linearity according to the invention of the apparatus according to the invention of +/−0.1 dB in the frequency range from 30 kHz to 30 MHz at a customary copper conductor pair impedance of, for example, Z=135Ω+/−20Ω(+/−15%), only a level correction of 40 dB has to be carried out when evaluating the measurement results of the spectrum analyzer.

In accordance with a further preferred embodiment of the present invention, it is provided that the apparatus has an output, wherein the output can be matched to different input impedances of a device connected to the output. It is thereby possible in an advantageous manner to obtain a very accurate and resilient measurement result of the measurement on the data transmission line.

According to the invention, it is preferably provided, in particular, that the apparatus is operated for measurement in copper conductor pair networks (i.e. networks comprising copper wire pairs or copper conductor pairs as data transmission lines within the meaning of the present invention) with a customary average impedance of 135Ω in conjunction with commercially available and suitable (and sufficiently accurate) generally portable spectrum analyzers operated with a rechargeable battery and having a symmetrical receiver input having an input or a measurement impedance Rmof approximately 100Ω to approximately 150Ω. However, the apparatus according to the invention can also be optimized or matched to frequency ranges or impedance relations other than those mentioned here merely by way of example (on the basis of the example of the typical impedance relations of the telecommunication network (primarily installed in Germany) of Deutsche Telekom)), in order to obtain the same advantages according to the invention, namely a simple, fast and at the same time comparatively highly accurate line measurement.

Further subject matter of the present invention relates to the use of an apparatus according to the invention for carrying out a measurement on a (generally permanently installed) data transmission line.

In this case, it is preferred that the data transmission line can be used uninterruptedly for the data transmission while the measurement is carried out. This is an essential advantage which makes the performance of the method not only simpler and faster, but at the same time also more accurate, since measurement is effected at the same (or unchanged) line configuration which is also used for the data transmission.

It is furthermore preferred that a copper wire pair, preferably a copper wire twisted pair, is used as the data transmission line, and/or that a spectrum analyzer for measuring the power spectral density of the radio-frequency signal transmitted on the data transmission line is connected to the apparatus, or for measuring interference voltages, and/or that the apparatus is matched to different input impedances of the spectrum analyzer.

Further subject matter of the present invention relates to a method for carrying out a measurement on a data transmission line provided for transmitting a radio-frequency signal and having a first line element and a second line element, wherein an apparatus for decoupling the radio-frequency signal comprises a tapping module and a current probe module, wherein the tapping module is connected to the first and second line elements at a first tapping location of the data transmission line for the purpose of decoupling the radio-frequency signal, and wherein the current probe module is coupled to the first line element at a second tapping location of the data transmission line for the purpose of decoupling the radio-frequency signal. Further subject matter of the present invention relates to a method for carrying out a measurement on a data transmission line (50) provided for transmitting a radio-frequency signal and having a first line element (51) and a second line element (52), wherein an apparatus (10) for decoupling the radio-frequency signal comprises a tapping module (20) and a current probe module (30), wherein the tapping module (20) is connected to the first and second line elements (51,52) at a first tapping location (61) of the data transmission line (50) for the purpose of decoupling the radio-frequency signal, and wherein

the current probe module (30) is coupled to the first line element (51) at a second tapping location (62) of the data transmission line (50) in the case of decoupling the radio-frequency signal, and

the current probe module (30) is coupled to the first and second line elements (51,52) at a second tapping location (62) of the data transmission line (50) in the case of decoupling the interference voltages.

In this case, it is preferred that a spectrum analyzer for measuring the power spectral density of the radio-frequency signal transmitted on the data transmission line is connected to the apparatus, wherein an output of the apparatus is matched to different input impedances of the spectrum analyzer.

Exemplary embodiments of the invention are illustrated in the drawing and explained in greater detail in the description below. The figures do not restrict the general concept of the invention.

FIG. 1schematically illustrates, in the sense of a block diagram, an apparatus10according to the invention for decoupling a radio-frequency signal transmitted on a data transmission line50. It goes without saying that the illustrated part of the data transmission line50represents in general merely a (small) part of the extent of the data transmission line50. The apparatus10comprises a tapping module20and a current probe module30. The tapping module20is connected to the data transmission line50at a first tapping location61. The current probe module30is connected to the data transmission line50at a second tapping location62. The data transmission line50has a first line element51and a second line element52, which are preferably provided as twisted line elements51,52of a copper wire pair (or copper conductor pair). Between the first tapping location61and the second tapping location62a distance is provided along the extent of the data transmission line50, said distance being illustrated by a double-headed arrow inFIG. 1. According to the invention, the distance between the first tapping location61and the second tapping location62is preferably from approximately 2 cm to approximately 200 cm, particularly preferably from approximately 5 cm to approximately 50 cm, especially preferably from approximately 8 cm to approximately 15 cm, and with even greater preference approximately 10 cm.

FIG. 2illustrates the operation of the apparatus10according to the invention for decoupling the radio-frequency signal (i.e. differential-mode operation), whileFIG. 4illustrates the operation of the apparatus10according to the invention for decoupling interference signals or interference voltages (i.e. common-mode operation).

FIG. 2represents a schematic illustration of the apparatus10according to the invention for decoupling the radio-frequency signal with greater detailing by comparison withFIG. 1. The apparatus10with its tapping module20and its current probe module30is once again illustrated. The illustrated part of the data transmission line50once again corresponds merely to a (small) part of the extent of the data transmission line50. The tapping module20preferably has a first tapping element21, and a second tapping element22. By means of the tapping elements21and22it is possible to realize an electrically conductive connection (in the sense of measuring electrodes) to the line elements51,52at the first tapping location61. The current probe module30preferably has a toroidal core magnet31, by means of which (via the measurement of the magnetic flux), the current flow through one of the line elements51,52of the data transmission line50can be measured. At the second tapping location62, the toroidal core magnet31of the current probe module30surrounds one of the line elements51,52.

In the connection example illustrated, the current probe module30is coupled to the first line element51or with the first line element51(at the second tapping location62) and the first tapping element21is connected to the first line element51and the second tapping element22is connected to the second line element52(at the first tapping location61). The apparatus10according to the invention comprises an output14, to which a spectrum analyzer40can preferably be connected, particularly if the power spectral density of the radio-frequency signal transmitted on the data transmission line50is intended to be measured.

An accurate determination of the power spectral density is required particularly when a plurality of data transmission lines potentially interacting with one another (for instance as a result of crosstalk) from different providers are utilized and it is necessary to ensure legally unequivocally that the coupling-in of signals (in particular into one or more of such data transmission lines by one of the providers) accords with the (statutory or regulatory) technical stipulations. This requires a high accuracy when determining the power spectral density, in particular.

InFIG. 2the radio-frequency signal propagates in accordance with the propagation direction55(i.e. from left to right in the figure). In this case, the first line element51corresponds to the a-conductor of the data transmission line50. The second line element52corresponds to the b-conductor of the data transmission line50. By way of example, the power P0(or power spectral density) coupled into the data transmission line50(by a signal providing device not illustrated) is to be measured. The current I0flowing in the first line element51is measured by means of the current probe module30. For this purpose, the current probe module30preferably has a secondary winding32around the cross section of the toroidal core magnet31, the current IS(current probe module current) being generated by means of said secondary winding or the current IS being induced in said secondary winding. The voltage U0between the line elements51,52is tapped off by means of the tapping module20, said voltage causing a current IT(tapping module current) in the apparatus10. On account of the directional coupler function of the apparatus10according to the invention, the radio-frequency signal (transmission signal) coming from the left is coupled to the output14of the apparatus10, wherein ISand ITmutually amplify one another (constructive interference). A radio-frequency signal coming from the right is largely suppressed (destructive interference of ISand IT). If the tapping elements21,22are interchanged, this situation is reversed.

The data transmission line50has an impedance of Z. At the output14of the apparatus10, the measurement voltage UM, the measurement current IMand the power PMare present for further processing by the spectrum analyzer40. In this case, the measurement current IMcorresponds to the (complex addition) of ISand IT. According to the invention, it is preferred for the apparatus10to comprise a changeover switch11(cf.FIG. 3), wherein the changeover switch11effects a circuitry interchange of the tapping elements21,22of the tapping module20. This means that in the case of connection of the first tapping element21to the first line element51and in the case of connection of the second tapping element22to the second line element52, a switch-over of the changeover switch11brings about a connection configuration of the apparatus10to the line elements51,52of the data transmission line50in such a manner as if the first tapping element21were connected to the second line element52and the second tapping element22were connected to the first element51. The sign of U0and thus of ITcan thereby be switched over. In the case of an optimum matching between the tapping module20and the current probe module30(given corresponding setting of the changeover switch11) ITand ISprecisely cancel one another out (i.e. they interfere destructively). When the tapping module20is accurately coordinated with the current probe module30, the apparatus10produces the function of a directional coupler.

In measurement operation (i.e. after a switch-over of the changeover switch11), constructive interference arises, i.e. a superposition, and IMcorresponds to the sum of ISand IT.

FIG. 3schematically illustrates an equivalent circuit diagram of the apparatus10according to the invention in the case of the use in accordance withFIG. 2. A printed circuit board or circuit board (not separately illustrated or designated) which is integrated for example into the current probe module30(for example in a manner accommodated in a handle of the current probe module, said handle being used at the same time for opening and closing the toroidal magnet31) has various circuit elements that are explained in greater detail below. The secondary winding32has N=15 turns, for example, such that IS0results as IS0=U0/(N×Z), i.e. UTcorresponds to U0divided by the product of the number of turns of the secondary winding32(or the turns ratio of primary and secondary windings31,32) and the impedance Z. A potentiometer P1(for example 500Ω) serves for exactly balancing the current probe module current ISwith the tapping module current IT(which is also designated as the sensing head current). Upon reversal of the signal direction (or propagation direction of the radio-frequency signal in the data transmission line50) or upon the switch-over of the changeover switch11, destructive interference of current probe module current ISand tapping module current ITarises. A further potentiometer P2(for example 5 kΩ) serves for balancing the measurement voltage UM, in particular to 40 dB decoupling attenuation. The measurement voltage UMis dropped across the input resistor RM(for example 135Ω) of the spectrum analyzer40. The changeover switch11is illustrated inFIG. 3and serves for interchanging the polarity of the sensing head current IT(or of the tapping module current). A tapping module cable25(also called sensing head cable) has a length of 40 cm for example, and has a very high characteristic impedance in order that the current probe module current ISflows primarily via the input resistor RMof the spectrum analyzer40. Preferably, the tapping module20comprises the tapping module cable25and a tapping module unit26having the components R1, C1and C2and test tips. The tapping module unit26is preferably fixedly connected to the tapping module cable25. In this case, the capacitance C1serves for the DC decoupling of the tapping module current IT. The sensing head resistor R1(for example in each case (i.e. twice) 9300Ω) serves for the high-resistance connection to U0across the power impedance Z (of the data transmission line50), which on average is 135Ω, for example. A variable capacitance C2(for example 0 to 2 pF), by means of insulated wires twisted over a length of approximately 1 to 4 cm, brings about a possibly required phase shift for additionally balancing the phases of the two currents ISand IT(such that, with good balancing, the difference between ISand ITapproximately vanishes, i.e. is approximately equal to 0). According to the invention, C2is coordinated for example with the length of the tapping module cable25(for example 40 cm) and the distance between the first and second tapping locations61,62(for example 10 cm). In general, C2cannot be set to the required magnitude with the aid of a trimming capacitor, since the minimum magnitude thereof is often too high (for example 1.5 to 5.5 pF).

According to the invention, it is advantageously possible that overdriving and the occurrence of intermodulation distortions in a spectrum analyzer40are avoided by means of the apparatus10according to the invention, in particular by means of the comparatively high decoupling attenuation. This, too, serves for increasing the accuracy when carrying out measurements of the connected spectrum analyzer40.

According to the invention, the toroidal core magnet31is, in particular, a hinged toroidal core magnet that can be opened by means of an actuation of tongs apparatus35(cf.FIG. 2) of the current probe module30.

FIG. 4represents a schematic illustration of the apparatus10according to the invention for decoupling the interference voltages. The apparatus10with its tapping module20and its current probe module30is once again illustrated. The illustrated part of the data transmission line50once again merely corresponds to a (small) part of the extent of the data transmission line50. The tapping module20preferably has the first tapping element21and the second tapping element22. By means of the tapping elements21,22it is possible to realize an electrically conductive connection (in the sense of measuring electrodes) to, on the one hand, the ring elements51,52and, on the other hand, ground of the data transmission line50at the first tapping location61. The current probe module30preferably has a toroidal core magnet31, by means of which (via the measurement of the magnetic flux) the current flow through both line elements51,52of the data transmission line50can be measured, wherein the two line elements51,52are enclosed in the same sense by the toroidal core magnet31at the second tapping location62.

In the connection example illustrated, the first tapping element21is connected to ground of the data transmission line50and the second tapping element22is connected to the first and second line elements51,52(at the first tapping location61). The apparatus10according to the invention has an output14, to which a spectrum analyzer40can preferably be connected, particularly if the interference signal on the data transmission line50is intended to be measured.

InFIG. 4, the interference signal or the interference voltage propagates in accordance with the propagation direction55(i.e. from left to right in the figure). In this case, the first line element51corresponds to the a-conductor of the data transmission line50. The second line element52corresponds to the b-conductor of the data transmission line50. The current ICMresulting from the current flows in the first and second line elements51,52is measured by means of the current probe module30. For this purpose, the current probe module30preferably has a secondary winding32around the cross section of the toroidal core magnet31, the current IS(current probe module current) being generated by means of said secondary winding or the current ISbeing induced in said secondary winding. The voltage UCMbetween, on the one hand, the two line elements51,52and, on the other hand, ground of the data transmission line50is tapped off by means of the tapping module20, said voltage causing a current IT(tapping module current) in the apparatus10. On account of the directional coupler function of the apparatus10according to the invention, the interference voltage signal coming from the left is coupled to the output14of the apparatus10, wherein ISand ITmutually amplify one another (constructive interference). A radio-frequency signal coming from the right is largely suppressed (destructive interference of ISand IT). If the tapping elements21,22are interchanged, this situation is reversed.

The data transmission line50has an impedance of Z. At the output14of the apparatus10, the measurement voltage UM, the measurement current IMand the power PMare present for further processing by the spectrum analyzer40. In this case, the measurement current IMcorresponds to the (complex addition) of ISand IT. According to the invention, it is preferred for the apparatus10to comprise a changeover switch11(cf.FIG. 5), wherein the changeover switch11effects a circuitry interchange of the tapping elements21,22of the tapping module20. This means that in the case of connection of the first tapping element21to ground of the data transmission line50and in the case of connection of the second tapping element22to the first and second line elements51,52, a switch-over of the changeover switch11brings about a connection configuration of the apparatus10to the line elements51,52of the data transmission line50in such a manner as if the first tapping element21were connected to the first and second line elements51,52and the second tapping element22were connected to ground of the data transmission line50. The sign of UCMand thus of ITcan thereby be switched over. In the case of an optimum matching between the tapping module20and the current probe module30(given corresponding setting of the changeover switch11) ITand ISprecisely cancel one another out (i.e. they interfere destructively). When the tapping module20is accurately coordinated with the current probe module30, the apparatus10produces the function of a directional coupler.

In measurement operation (i.e. after a switch-over of the changeover switch11), constructive interference arises, i.e. a superposition, and IMcorresponds to the sum of ISand IT.

FIG. 5schematically illustrates an equivalent circuit diagram of the apparatus10according to the invention in the case of the use in accordance withFIG. 4. A printed circuit board or circuit board (not separately illustrated or designated) which is integrated for example into the current probe module30(for example in a manner accommodated in a handle of the current probe module, said handle being used at the same time for opening and closing the toroidal magnet31) has various circuit elements that correspond to the circuit elements in accordance with the description ofFIG. 3. Only the differences are explained in greater detail below.

Preferably, the tapping module20comprises the tapping module cable25and a tapping module unit26having the components R1, R1/2, C1and L1and test tips. The tapping module unit26is preferably fixedly connected to the tapping module cable25. In this case, the capacitance C1serves for the DC decoupling of the tapping module current IT. The sensing head resistor R1(for example in each case (i.e. twice) 9300Ω) serves for the high-resistance connection to UCMacross the line characteristic impedance ZCM(of the data transmission line50), which on average is 55 to 60Ω, for example. An inductance L1is bifilar for the common-mode current ICM, but suppresses the flow of the differential current fundamentally present between the first line element51and the second line element52. L1is additionally connected in series with the two resistors R1. The resistor R1/2corresponds, for example, to a value of 4650Ω.

According to the invention, the toroidal core magnet31is, in particular, a hinged toroidal core magnet that can be opened by means of an actuation of tongs apparatus35(cf.FIG. 2) of the current probe module30.