EP2328288B1 - System for detecting and localising impedance error adjustments - Google Patents

Description

The present invention relates to a system for detecting and locating impedance mismatches in a SMATV network.

The invention relates to the field of reflectometry in the frequency range, specifically the field of detection and localization of impedance mismatches within SMATV networks (SMATV = satellite master antenna television; community television antenna system), with only signals from these networks being used without any other signal is inserted by the system according to the invention.

State of the art

The distribution networks for TDT services and satellite television systems contain, depending on their structural design, a large number of impedance matching deficiencies (impedance mismatches) on the transmission lines on which high-frequency signals are transmitted from the head unit to the user socket. The reflected waves appear in essentially all those discontinuities that are present in SMATV networks, that is, in connections between distributors, downcomers, sockets and in coaxial cables, due to the fact that the devices used in the network are not ideal. This can lead to echoes with short recognition times that are located in key points in the network; and another group of mismatches can occur, caused by defective or disconnected cables, by the poor condition of the distribution elements and also by faults during installation that are difficult to identify.

The effect of an impedance mismatch at a certain point in a SMATV network is that a reflection or an echo of the signal is generated at that point with a different amplitude and phase. Reflections can influence the signal distribution in the rest of the network in a constructive or destructive form due to the aforementioned change in amplitude and phase in the reflected signal. Hence, a network that has been inappropriately treated can show undesirable effects. As a result of these reflections, the signal can be significantly affected in its performance, so that some of the services cannot be provided to some users.

This is true in the case of digital terrestrial transmission signals, particularly in the case of satellite signals, where the existence of techniques to protect against errors due to inter-symbol interference (ISI) is very limited.

Another critical case is when data is sent over coaxial cables, again because multipath phenomena lead to interference between symbols.

Although the actual construction of these networks can usually mitigate the consequences of the existence of the signal bouncing in the rest of the network, the stage at which the network is installed is necessary for the correct reception of the signal in these networks in order to detect any delayed signals, which are or are not intended in the stage of development or construction, and which were triggered by the uncontrolled, previously commented motifs.

Today, the solutions available in the field of impedance mismatch detection envisage that the position of these disturbances is obtained by inserting a known signal, and by later receiving (intercepting) the signal caused by the separation of the impedances. Logically, when using these facilities, SMATV networks are used where no other signal is inserted that is not a signal from the actual facility. There are different scenarios in which this happens. The first situation is when the network is still in the installation phase. In this case, no signal is transmitted to any of the possible users of the network, so that there is also no possibility of interfering with the needs of the users. In the second case, a network is fully functional, but in order to identify the reflections it is necessary to separate the signal from the head unit so as not to interfere with the measurement process. Of course, this is an undesirable situation because it involves the termination of services for various users connected to the SMATV network.

There is currently no technology available to determine the origin of the impedance mismatches in the network without depriving the user of services that he uses. Therefore, every time one begins to search for the position of the decoupling or echoes within a SMATV network, it becomes necessary to stop the propagation of the signal, which interrupts the reception of content in each of the distribution sockets, with the corresponding disadvantage for the group of Users who want to use the services offered.

As already stated, the current focus for determining the presence of mismatches when matching impedances is essentially based on the insertion of a known signal into the network and on the subsequent reception (interception) of the reflections that result in decoupling of the network (reflectometry). have their origin. Depending on the type of domain that is being worked in, i.e. time or frequencies, there are two possible ways to solve the problem. Reflectometry in the domain of time (TDR) consists in transmitting a pulse to the device to be evaluated and in the interception of the reflected signal in the device. This technique is often used to study the parameters of lossy transmission lines, as for example in the American patent US 006437578B1 labeled, "Cable Loss Correction for Distance to Fault and Time Domain Reflectometer Measurements." The sampling rates in the acquisition (interception) of the signal in the field of reflectometry in the time domain require the use of clocks that are too high, which increases the complexity of the recognition tools. Due to the limitations of the TDR system to check the existence of errors in function as a function of the frequency in the system to be analyzed, a completely different procedure results. This consists in the well-known reflectometry, which works in the frequency domain (FDR). This is a very frequently used strategy in measuring devices due to the need for a lower sampling rate (therefore less complex) and the increased measure to observe the spectral variation of the process parameters. This technique creates spectral noise, usually with a tone or series of tones, so the effects of impedance mismatches versus frequency are obtained from the reflection of these sinusoids. Examples of the use of this technique are the US patents US 006868357B2 with the title "Frequency Domain Reflectometry for testing wires and cables utilizing in situ-connectors, passive connectivity, cable fray detection, and live wire testing" and US 006691051B2 entitled "Transient distance to fault measurement".

There are several variants in the known frequency range of reflectometry. So there is the phase detection FDR (PDFDR), which the phase difference between the waves, the "standing wave reflectometry (Standing Wave Reflectometry SWR), which produces the size of the standing wave by the superposition of the incident and reflected waves, calculates the size of the Waves, the frequency-modulated continuous wave (FMCW), which uses a set of sinusoids whose frequency is increased linearly, and the mixed-signal reflectometry (MSR) as in the US patent US007215126B2 illustrated, entitled "Apparatus and method for testing a signal path from an injection point "and in" Mixed-Signal Reflectometer for Location or Faults on Aging Wiring "," Peijung Tsai et al, IEEE Sensors Journal, vol. 5, No. 6 December 2005 , a technique that uses the sum of two sine waves, one incident and one reflected, and which extracts the DC component that is the result of obtaining the square of this operation.
In addition to the tools described, there are other options for the detection of signal reflections for the common use of reflectometry in time and frequency. This third way is called Time-Frequency Domain Reflectometry (TFDR), see the European patent EP 1477820 A2 entitled "Wire fault detection" or the publication IEEE Transactions on Instrumentation and measurement, Vol. 54, No. 6, December 2005 entitled "Application of time-frequency domain reflectormety for detection an localization of an fault on a coxial cable" by Yong-Juni Shin, and Edward J. Powers , with examples of their use.

The common point of all the technologies described so far is the use of a signal generated internally to perform the measurements and, occasionally, the use of other equipment to correctly perform the proposed actions. The insertion of the network signal and the interception of the reflections must be done at the same physical point, with the hardware complexity necessary to use a device to separate the reflected signal from the transmitted signal. This approach is not arbitrary because if the signal is generated somewhere else on the network that is not the same as where the reflection is intercepted, it is desirable not only to include the various components of the detection, the transmitter and the receiver It is also essential to analyze the network down to the last detail in order to be able to predict the effect and position of the delayed components of the main signal based on both signals. The fact of inserting a known signal in the network and capturing the reflection at the same point places direct demands on the hardware design of the device in question and significantly increases its complexity. In addition, locating the origin of the reflected waves requires that the signal be sampled at a speed high enough to distinguish very close echoes. The greater the spatial accuracy is desired, the higher the sampling rate has to be. In addition, another of the many shortcomings of current mismatch detectors is, as has been seen, the need for the device to enter a known signal into the network, and it is appropriate to do so temporarily suspend providing services, which is undoubtedly a disadvantage for the user.
Finally, if the technical staff who are responsible for performing these tasks wish to limit the search for delays to a certain area of the SMATV network, the corresponding network components must be physically disconnected, thereby reducing the services offered to the users of these Networks are restricted.

U.S. 6,278,730B1 discloses a non-invasive digital cable test system. In this system, an estimation of an "in-phase error correlation signal", a "quadrature error correlation signal" and a "cross-correlation signal" is required. The system has a complex design and includes, among other things, an equalizer (equalizer 236, 214, 752) and a demodulation unit (606).

US 6,687,632 B1 discloses a method for testing CATV systems. The method assumes the input of a pseudo-aleatoric signal (formed by the circuit 20) into the respective system.

DESCRIPTION

The invention is based on the object of creating a system for detecting and locating impedance mismatches in a SMATV network, which is designed to be simple in terms of its hardware and software structure.

This object is achieved by a system which is defined in the claims. Only the spectral shape of the channels transmitted in a SMATV network is used in order to obtain information about the impedance mismatches in this system, in particular as defined in the claims.

The present invention has a number of advantages.

An advantageous embodiment of the invention is formed by a system for the detection and localization of impedance mismatches in a SMATV network according to patent claim 1.

This has the advantage that no signal has to be entered into the SMATV network, which is also associated with the further advantage of lower complexity and lower costs for the system.

An advantageous exemplary embodiment of the invention is characterized in that the system is designed in such a way that the resolution of the room recognition, the bandwidth used and the rank of the room recognition are varied.

Another advantageous embodiment of the invention is characterized in that the system is designed in such a way that the results that were determined in different measurements at various points in the SMATV network are compared with one another. This has the advantage that the origin of the various impedance mismatches can be distinguished in the case of ambiguous situations.

In the following, the advantages and the properties of the invention are explained on the basis of the following description, in which reference is made to the accompanying figures.
Figure 1 Figure 12 is a block diagram showing details of the system and method for detecting and locating impedance mismatches. At point 101, the spectrum of the signal is obtained that is used to identify and localize the position of the mismatches. The spectrum obtained contains information about the presence of impedance mismatches in the network according to the following equation: $$X_{\mathit{rec}}\left(\omega \right)=X\left(\omega \right)+{\displaystyle \sum _{k=1}^K\left\{{\rho }_{{\mathrm{R.}}_k}X\left(\omega \right)+{\rho }_{{\mathrm{I.}}_k}\stackrel{⌢}{X}\left(\omega \right)\right\}{e}^{{\mathit{j\omega \tau }}_k}}$$

ist die Hilbert-Transformierte), ρ_Rk y ρ_Ik sind die Real- bzw. Imaginärteile eines jeden der K Reflexionskoeffizienten, die den verschiedenen Impedanz-Fehlanpassungen im SMATV-Netz zugeordnet sind und τ_k ist die Verzögerung einer jeden Replik, die durch dieses Fehlanpassungen bezüglich des direkten Signals X(ω) gebildet ist.
Die maximale Bandbreite des verwendeten Signals ist begrenzt auf den entsprechenden Rang der Verbreitung oder Signale innerhalb eines SMATV-Netzes, wobei es möglich ist, eine geringere Bandbreite zu verwenden. Die verwendete Bandbreite ist direkt verbunden mit der Zeitauflösung, die verwendet wird bei der Erkennung der Reflexionen entsprechend der Gleichung Tc = 1/B, wobei Tc die Periode des zeitlichen Abtastens und B die Bandbreite des verwendeten Signals ist. So weisen die Raumauflösung der vorliegenden Erfindung und die Zeitauflösung eine proportionale Beziehung auf, abgeleitet aus der Gleichung D = vp·Tc, wobei D die Raumauflösung und vp die Geschwindigkeit der charakteristischen Ausbreitung des Koaxialkabels ist. Nachdem das Spektrum des Signals gewonnen ist, gewinnt man das Modul dieses Spektrums im Block 102. Nachdem das Spektrum des ausgewählten Signals gewonnen ist, wird im Block 103 eine Reduktion des Geräusches vorgenommen, das in dem Spektrum vorliegt. Das resultierende Signal ist Gegenstand von Spektraltransformationen im Block 104, wo die Erhebung des Signalmoduls um einen Faktor n im Block 1041 erfolgt, wobei der Wert n = 2 lediglich ein nicht einschränkendes Beispiel eines auszuwählenden Faktors dargestellt. So ergibt sich am Ausgang dieses Blockes $${\left|X_{\mathit{rec}}\left(\omega \right)\right|}^2={\left|X\left(\omega \right)\right|}^2{\left|H\left(\omega \right)\right|}^2$$

mit $${\left|H\left(\omega \right)\right|}^2={\left|1+{\displaystyle \sum _{k=1}^K\left\{{\rho }_{R_k}+{\rho }_{I_k}{e}^{-j\frac{\pi }{2}}\right\}{e}^{{\mathit{j\omega \tau }}_k}}\right|}^2$$

In the aforementioned equation, X _rec ( ω ) corresponds to the Fourier transform of the signal received at a specific point in a SMATV network in which there are K impedance mismatches. X ( ω ) is the Fourier transform of the signal that is transferred to the SMATV network without being modified by the effect of the mismatches (

is the Hilbert transform), ρ _{R k} y ρ _{I k} are the real or imaginary parts of each of the K reflection coefficients associated with the various impedance mismatches in the SMATV network and τ _k is the delay of each replica that is formed by this mismatch with respect to the direct signal X ( ω ).
The maximum bandwidth of the signal used is limited to the corresponding rank of distribution or signals within a SMATV network, whereby it is possible to use a lower bandwidth. The bandwidth used is directly related to the time resolution used in detecting the reflections according to the equation Tc = 1 / B, where Tc is the period of the temporal sampling and B is the bandwidth of the signal used. Thus, the spatial resolution of the present invention and the time resolution have a proportional relationship derived from the equation D = vp * Tc, where D is the spatial resolution and vp is the velocity of the characteristic propagation of the coaxial cable. After the spectrum of the signal has been obtained, the module of this spectrum is obtained in block 102. After the spectrum of the selected signal has been obtained, in block 103 made a reduction in the noise present in the spectrum. The resulting signal is the subject of spectral transformations in block 104, where the signal module is raised by a factor n in block 1041, the value n = 2 merely representing a non-limiting example of a factor to be selected. So it results at the exit of this block $${\left|X_{\mathit{rec}}\left(\omega \right)\right|}^2={\left|X\left(\omega \right)\right|}^2{\left|H\left(\omega \right)\right|}^2$$

With $${\left|H\left(\omega \right)\right|}^2={\left|1+{\displaystyle \sum _{k=1}^K\left\{{\rho }_{{\mathrm{R.}}_k}+{\rho }_{{\mathrm{I.}}_k}{e}^{-j\frac{\pi }{2}}\right\}{e}^{{\mathit{j\omega \tau }}_k}}\right|}^2$$

wobei A_k und B_k Konstanten sind, die den Einfluss eines jeden Koeffizienten der Impedanz-Fehlanpassungen umfassen, die in dem SMATV-Netz vorhanden sind hinsichtlich einer jeden Verzögerung τ_k , die durch eine konkrete Fehlanpassung gebildet ist. Auf diese Weise ergibt sich, dass die Wirkung der Fehlanpassungen auf das Spektrum des in dem SMATV-Netzes übertragenen Signals sich umsetzt in deren Multiplikation durch die Summe einer Reihe von Signalen, die aus Sinusoiden abgeleitet sind.
Nachdem das Signal am Ausgang des Blockes 1041 gebildet ist, dient dieses als Eingangssignal für den Block 1042, in dem eine Transformation des Spektrums vorgenommen wird, das ermöglicht, das über das SMATV-Netz übertragene Signal von den Wirkungen des Netzes besser abzukoppeln. Ein nicht einschränkendes Beispiel ist die Anwendung einer logarithmischen Funktion, ein Logarithmus auf der Basis 10, was ermöglicht, die Wirkung der Fehlanpassung auf das übertragende Signal abzutrennen.In the latter equation, expanding the square of the module gives the following equation: $${\left|H\left(\omega \right)\right|}^2=1+{\displaystyle \sum _{k=1}^K{\mathrm{A.}}_k\cos \left({\mathit{\omega \tau }}_k\right)}+2{\displaystyle \sum _{k=1}^{K-1}{\displaystyle \sum _{r=k}^K{\mathrm{B.}}_k\cos \left(\omega \left|{\tau }_k-{\tau }_r\right|\right)}}+{{\displaystyle \sum _{k=1}^K\left|{\alpha }_k\right|}}^2$$

where A _k and B _{k are} constants comprising the influence of each coefficient of the impedance mismatches present in the SMATV network with respect to each delay τ _k formed by a particular mismatch. This means that the effect of the mismatches on the spectrum of the signal transmitted in the SMATV network is converted into its multiplication by the sum of a series of signals derived from sinusoids.
After the signal is formed at the output of block 1041, it is used as an input signal for block 1042, in which a transformation of the spectrum is carried out, which enables the signal transmitted via the SMATV network to be better decoupled from the effects of the network. A non-limiting example is the use of a logarithmic function, a logarithm on the base 10, which enables the effect of the mismatch on the transmitted signal to be separated.

wobei $$10{\log }_{10}\left({\left|H\left(\omega \right)\right|}^2\right)=10{\log }_{10}\left(1+2{\displaystyle \sum _{k=1}^K{A}_k\cos \left({\mathit{\omega \tau }}_k\right)}+2{\displaystyle \sum _{k=1}^{K-1}{\displaystyle \sum _{r=k}^K{B}_k\cos \left(\omega \left|{\tau }_k-{\tau }_r\right|\right)}}+{\displaystyle \sum _{k=1}^K{\left|{\alpha }_k\right|}^2}\right)$$

Applying this transformation to the previous equations results in the following equation $$\begin{array}{lll}10{\log }_{10}{\left|X_{\mathit{rec}}\left(\omega \right)\right|}^2& =& 10{\log }_{10}\left({\left|X\left(\omega \right)\right|}^2{\left|H\left(\omega \right)\right|}^2\right)\\ & =& 10{\log }_{10}\left({\left|X\left(\omega \right)\right|}^2\right)+10{\log }_{10}\left({\left|H\left(\omega \right)\right|}^2\right)\end{array}$$

in which $$10{\log }_{10}\left({\left|H\left(\omega \right)\right|}^2\right)=10{\log }_{10}\left(1+2{\displaystyle \sum _{k=1}^K{\mathrm{A.}}_k\cos \left({\mathit{\omega \tau }}_k\right)}+2{\displaystyle \sum _{k=1}^{K-1}{\displaystyle \sum _{r=k}^K{\mathrm{B.}}_k\cos \left(\omega \left|{\tau }_k-{\tau }_r\right|\right)}}+{\displaystyle \sum _{k=1}^K{\left|{\alpha }_k\right|}^2}\right)$$

und die entsprechende Beziehung mit dem Logarithmus auf Basis 10 $${\log }_{10}\left(x\right)=\frac{\ln \left(x\right)}{\ln \left(10\right)},$$

impliziert das Ergebnis, den Logarithmus auf das Signal |X_rec (ω)|² anzuwenden, die Umwandlung des Produkts |X(ω)|² y |H(ω)|² in eine Summe zu der Zeit, die diese letzte Funktion fortführt, wobei diese gebildet wird durch eine Kombination der Signale, die aus Sinussoiden abgeleitet ist.Taking into account the Taylor approximation of the Neperiano Logartihmus function $$\ln \left(1+x\right)={\displaystyle \sum _{n=1}^{\infty }\frac{{\left(-1\right)}^{n+1}}{n}{x}^n}$$

and the corresponding relationship with the logarithm based on 10 $${\log }_{10}\left(x\right)=\frac{\ln \left(x\right)}{\ln \left(10\right)},$$

implies the result, the logarithm on the signal | X _rec ( ω ) | ² apply the transformation of the product | X ( ω ) | ² y | H ( ω ) | ² into a sum at the time this last function continues, this being formed by a combination of the signals derived from sinusoids.

After these transformations have been applied, the Inverse Fourier Transform (IFT) of N points is formed (block 105). The number N limits the rank of the detectable mismatches to N · D / 2, since the application of IIFT is applied to a real signal and one obtains a complex symmetrical signal so that one can exclude half of the points.

As a result of this block, a process of the time response 106 is applied, which consists in obtaining the module 1061 of the resulting complex signal and the subsequent elevation to a known power 1062. The result is converted into a A plurality of maxima whose time position corresponds to each of the delays τ _k , which corresponds to each impedance mismatch in the SMATV network.
After the results of the aforementioned blocks have been formed, a normalization 107 is formed, which enables a comparison between various measurements that are made in the entire SMATV network.

The resulting signal is similar to the signal shown in Figure 4 is reproduced where because of the periodicity of the input spectrum, as from Figure 8 it can be seen that false positives can occur that can easily be confused with actual impedance mismatches. These false positives can be easily detected by calculating the periodicity of the input spectrum and they can be removed by comparing the spectra formed at different points of the SMATV network and using the difference as the input of the system according to the invention, with results obtained in Figure 5 are shown.

The process of recognizing and localizing the impedance mismatches ends with the recognition of the maxima in the signal 108 and with the acquisition of the special position associated with the time delay of the different maxima of the signal.

Description of the figures

Figure 1

Detection of impedance mismatches

101, OE

Formation (acquisition) of the spectrum

102

Block of formation of the spectrum module

103

Noise reduction.

104

Transformation of the spectrum

105

Inverse Fourier transform of N points

106

Processing the time response

107

Normalization.

108, DM

Detection of maximum values

Figure 2

Spectral transform block

1041

Block of square formation

1042

Block of transformation of the spectrum

Figure 3

Time response processing block

1061

Block of formation of the spectrum module

1062

Block of square formation

Figure 4

Components resulting from the shape of the input signal

Figure 5

Detection of the position of the impedance mismatches.

Figure 6

SMATV network that measures TV signals or some other known signal

201

Satellite signal antenna

202

mixer

203

Derivative components

204

Distribution network

205

Utility sockets

206

Location device

207

Coaxial cable

Figure 7

Embodiment of the invention

301

Input terminal of the signal

302

Device for energy detection

303

mixer

304

Band pass filter

305

Local oscillator for intermediate frequency signal

306

Automatic Gain Control Circuit (AGC)

307

Analog-to-digital converter (A / D)

308

Microprocessor control

309

Interface with user

310

Optical end device

311

FPGA

Figure 8

Sets of satellite programs in the IF band FI

Figure 9

Another embodiment of the invention

401

Satellite signal antenna

402

mixer

403

Excerpt from a distribution network of unknown network topology

404

Derivative element

405

Coaxial cable of unknown length

406

Device for localizing impedance mismatches

407

Distribution network

Figure 10

Another embodiment of the invention

501

Satellite signal antenna

502

mixer

503

Excerpt from a distribution network of unknown network topology

504

Derivative element

505

Coaxial cable of unknown length

506

Device for localizing impedance mismatches

507

Distribution network

Description of a preferred embodiment of the invention

A preferred exemplary embodiment of the invention is described below without excluding other embodiments of the invention. The following description illustrates the features and advantages of the present invention using one of many embodiments.

Figur 6

in vereinfachter Darstellung den Weg des Signals in einem SMATV-Netz bis zu dem erfindungsgemäßen System der Erkennung und der Lokalisierung von Fehlanpasungen;

Figur 7

ein Schema des Systems zur Erkennung und Lokalisierung von Fehlanpassungen gemäß der Erfindung;

Figur 8

ein Beispiel eines Spektrums, das zur Erkennung und Lokalisierung von Impedanz-Fehlanpassungen verwendet wird,

Figur 9

die Verwendung des erfindungsgemäßen Systems zur Messung der Länge eines Koaxialkabels; und

Figur 10

die Verwendung des erfindungsgemäßen Systems zur Erkennung der Entfernung zu einem Ausfall.

A non-limiting example of the preferred embodiment will now be described with reference to the following figures:
It shows

Figure 6

a simplified representation of the path of the signal in a SMATV network up to the inventive system of detection and localization of incorrect adaptations;

Figure 7

a scheme of the system for detection and localization of mismatches according to the invention;

Figure 8

an example of a spectrum used to detect and locate impedance mismatches,

Figure 9

the use of the system according to the invention for measuring the length of a coaxial cable; and

Figure 10

the use of the system according to the invention for detecting the distance to a failure.

Figure 6 shows a simplified representation of a SMATV network in which the detection and localization of mismatches takes place. The block 201 corresponds to a satellite signal receiving antenna which positions the signal received in the IF band in the range between 950 and 2150 MHz. The signal from block 201 is mixed with a terrestrial TV signal and transmitted to distribution network 204. The mismatches in the derivation components 203 and in the sockets 205 are added to the input signal in the network 204, they are transmitted via the coaxial cable 207 to the system 206 for detection and localization of the mismatches.

Figure 7 shows a schematic representation of the system of detection and localization of mismatches. The signal comes into the system via 301. The block 302 is a device for detecting the energy (power detector), which is used to inform the module 308 that a signal is present at the input. The module 308 is the heart of the system and its mission is to organize the steps that the other blocks that are part of the global system have to follow depending on user instructions displayed via the interface 309, as well as the steps of the Power detector 302. The RF signal is converted to a known intermediate frequency by means of the oscillator 305 and the mixer 303. The bandpass filter 304 has the task of limiting the bandwidth that is used in the formation of the spectrum, whereby the signal that corresponds to the neighboring frequencies is eliminated, so that only the band of interest that is digitized by the analog-to-digital converter 307 remains.
In this application example of the invention, the gain level of the signal is adjusted in advance with a gain control 306 in order to cover the entire dynamic range of the analog-digital converter and thus to reduce the quantization errors. After digitization, the signal is passed to the system 311, in which the necessary samples are taken to obtain the spectrum of the frequency range that is being used. After the samples are acquired, their frequency response is obtained and this is communicated to system 308 using any suitable communication interface. Not in this one As a restrictive example, the system 311 is an FPGA (Field Programmable Gate Array). The system 308 calculates the location of the impedance mismatches. Block 308 will also adjust the frequency of the signal to capture the signal and thus shape the spectrum of the satellite band, an example of a resulting spectrum is in FIG Figure 8 shown.

The user of the present invention can communicate with block 308 via user interface 309.
Figure 9 Figure 11 shows a situation in which the present invention is used. This representation does not represent a restriction neither with regard to the implementation nor with regard to the scope of the present invention. The system shown measures the unknown length L of a cable 406 which is located in a SMATV network 407 in which an area 403 exists whose topology is not known is. The cable 406 and the system 406 for the detection and localization of mismatches are connected to a switch (diverting element) 404.
Figure 10 FIG. 8 shows, as an example, a system which determines the unknown distance to the fault location LF within a cable 505 of length Lc which is arranged in a SMATV network 507. The network has a part 503, the topology of which is not known. The cable 505 and the system 506 for the detection and localization of mismatches are connected to a switch (diverting element) 504.
This preferred embodiment, which does not constitute a restriction on the implementation of the invention or the scope of the present invention, relates to a system for the detection and localization of impedance mismatches in SMATV networks.
The system according to the invention is designed in such a way that input signals in a SMATV network are signals that are not input from outside through or into the system.
System-internal signals are used to identify and localize impedance mismatches.

Claims (3)

1. System for detection and localization of impedance mismatches in SMATV-networks, which comprises:

   - a radio frequency input (301) for receiving a signal in a point of the SMATV network;

   - a device (302) for detecting energy of this signal;

   - a mixing stage (303) for converting this signal;

   - a bandpass filter (304) for filtering the converted signal;

   - an automatic gain control circuit (306) for adapting the filtered signal;

   - an analog-to-digital converter (307) for digitalization of the adapted signal;

   - a module for detection and localization of impedance mismatches (308, 311), which comprises:

   a first block (101) configured for calculation of a spectrum of the signal digitized by the analog-to-digital converter;

   a second block (102) configured for calculation of a module of the spectrum of the signal is;

   a third block (103) configured to reduce the noise of the module of the spectrum of the signal;

   a fourth block (104) configured to spectrum transform the noise-reduced module of the spectrum of the signal, wherein the spectrum transform comprises performing an operation (1041, 1042) with the noise-reduced module to the nth power;

   a fifth block (105) configured for calculation of an inverse Fourier-transformed (IFT) of the transformed noise-reduced module of the spectrum of the signal;

   a sixth block (106) configured for calculation of a module to the n-th power of the inverse Fourier-transformed (IFT) of the transformed noise-reduced module of the spectrum of the signal; and

   a seventh block (108) configured to detect and localize impedance mismatches in the SMATV-network at the positions of maxima in the module to the nth power of the inverse Fourier transform of the transformed noise-reduced module of the spectrum of the signal.
2. System according to claim 1, wherein a spatial resolution of the detection, a used bandwidth and a spatial detection range for detection and localization of impedance mismatches can be set.
3. System according to claim 1, further comprising an eight block for performing a normalization operation (107) of the module to the nth power of the inverse Fourier transform of the transformed noise-reduced module of the spectrum of the signal (106), wherein the system is configured to compare impedance mismatches detected and localized in different points of the SMATV-network.

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