Search device for the localisation of a transmitter, in particular search device for avalanche victims

The invention relates to an apparatus for searching a transmitter, in particular avalanche-victim search device, wherein for scanning a search area the search device is swiveled by a user in an angular range that covers the search area.

Avalanche transceiver search devices operate with an unmodulated transmission signal at 457 kHz. All skiers in a group turn in normal operation their equipment to transmission mode. If a part of the group buried in an avalanche, turn the other people their devices to receive and attempt to locate the victim on the basis of the transmitted signal.

The transmission signal is clocked at a frequency of approximately one Hertz. The transmission time at the frequency of 457 kHz, the so-called. Duty cycle is ten to 30 percent.

Enables remote location by ear (or maximum / minimum field strength) conventional devices from the transmission signal generating at 457 kHz by down-mixing an audible search tone at a frequency of about 2 kHz. Since the built-in antenna has a pronounced directional characteristic, the direction of maximum field strength of the buried transmitter can be determined by turning the receiving device and search for the volume maximum or minimum. This technique requires the seeker high concentration, exercise, and especially for larger distances low ambient noise.

In order to simplify the seeker without exercise stress situations and in the search, with a plurality of devices, at right angles to each other arranged antennas have been developed. By switching between these antennas and the receive direction of the transmission signal can be determined (see this AT 006 120 U2;. DE 101 09 284 A1).

This method has a number of disadvantages in practice. Firstly, the antennas affect each other, even if they are turned off so that the receiver sensitivity of the device overall suffers. In particular, a direction determination is almost impossible at great distances over 50 meters, the direction indicator thus obtained therefore not be used. Secondly, this technique is very sensitive to interference, so that the direction indicator varies widely in less than optimal conditions.

A particular challenge for the seeker is when he receives the signals several buried at the same time. The localization by ear requires here an extraordinary amount of exercise and a cumbersome search strategy. A corresponding procedure is described in EP 0733916 A2, wherein a better positioning is achieved in that the transmitter transmits with three mutually orthogonal antennas. After determining the search direction this direction can be followed by means of an electronic compass.

The DE 299 22 217 U1 are engaged in the search of buried. Here GPS coordinates are compared. To the search of avalanche GPS receivers are too imprecise and prone to failure.

Starting from EP 0733916 A2 it is an object of the present invention to provide a generic detector, which determines the position of at least one buried in a reliable and cost-effective manner automatically.

This object is achieved by a detector having the features of claim 1 and a positioning method having the features of claim sixteenth

An essential idea of ​​the invention is that a search device that solves the above object, ideally operate like a radar and the antenna would constantly at an angular range, for example. 180 degree turn. Because it is known, the angle at which the antenna is straight, a received signal with the respective field strength can be associated with the current angle of the antenna at any time. This is so in practice, of course not feasible. After all, but the rotation is achieved by 180 degrees by the fact that the examiner holds the device while walking in hand and swings to the left and right, a procedure, as is known in the use of detection equipment according to the prior art. The problem then is to determine the angle at which the device is to an external reference coordinate system at a given time.

The idea of ​​generating from the transmitter signals and the sensor signals angle signals representing a received signal strength in response to a search angle, solves this problem. The use of signal-processing mechanisms to the angle signals according to the invention allows the determination of the transmitter site in a particularly simple and reliable manner.

In principle it is possible to obtain information about the current search angle by analyzing the signals from acceleration sensors or rotary sensors. In practice, initial value problems and the constant acceleration of gravity lead to large errors in this case.

Also information about the search angle may could be obtained from the evaluation of the GPS signal. Are contrasted by the relatively high cost of a GPS receiver and - contrary to generally inadequate availability of sufficient GPS signals - for rescue applications.

According to the Earth's magnetic field is used as such a solid and permanently available reference coordinate system. So that is possible at a fixed search angle at any time, the allocation of the received transmitter signal of a transmitter.

In a preferred embodiment of the search device according to the invention the magnetic field sensor outputs three Earth's magnetic field corresponding sensor signals to the signal processing device. This allows the solid angle of the device to determine relative to the field lines, in which the field strength components of the Earth's magnetic field are measured in three mutually perpendicular axes.

In addition, magnetic field sensors with an accuracy of 1 degree cheaper than a GPS receiver, so that search device according to the invention can be manufactured more cheaply.

In another embodiment, tilt sensors are provided, the output sensor signals to the signal processing device, which based the location of the search device represent a horizontal plane. From the sensor signals of the inclination sensors, the sensor signals of the magnetic field sensor can be corrected advantageously so that the relative position of the search device to Earth's magnetic field can be very accurate and completely independent of the horizontal position of the search device can be determined.

In another embodiment, especially of the aforementioned embodiment, the signal processing means for calculating a channel scan angle at which the transmitter is located, formed the basis of the angle signals. This can be determined by the search unit of the location of the transmitter, since the determination of the distance between transmitter and detector by conventional methods is easily possible. A determination of the transmitter site by ear is not required. The transmitter search angle can be determined by one or more times swiveling the search device according to the invention, even if the device has already been back in a completely different direction.

In a further aspect of this embodiment the signal processing means is configured to determine from at least two angle signals the transmitter search angle.

One problem with transmitters to locate Spilled is that the transmitter signal from the transmitter is clocked. With a random swiveling movement so it will often happen that the channel is in a silent period when the detector towards maximum or minimum field strength (during the times at which the transmitter sends) is held. The sequence of angle signals, ie, the function of the received signal strength over the search angle is, therefore, generally only as portion present. It is advantageous, therefore, the search unit, an algorithm implemented to extrapolate from the intermediate values ​​maximum and minimum. In principle, this arbitrary two points of the field strength curve (ie two angle signals) are required when the directivity of the search antenna is known.

These are the - as described previously for the search angle and subsequently for the field strength - acquired images (Time -> search angle) and (Time -> field strength) in a picture (search angle -> field strength) transformed. In a particularly advantageous embodiment of the search device according to the invention is the extrapolation or interpolation of the full course of the figure (search angle -> field strength) carried out by applying the method of least square. This allows a continuous improvement of the estimated field strength curve over the search angle with further measurements.

In further embodiments, the search device according to the invention, the output unit for the graphical output of result signals is formed, representing the transmitter search angle, and in particular a display panel graphic display of the transmitter site included in the search area. This quick and intuitive grasp of the transmitter site is made possible by the user advantageously.

In further embodiments, the search device according to the invention the signal processing means comprises a filter correlation unit that is designed to detect angle signals by correlating the transmitter signals (reception signal and down mixed reception signal) with predetermined pattern or filter signals. This detecting weak signals from a transmitter is enabled, the. Is located for example at a great distance from the detector. This corresponds to detecting a signal of known form in noise. On the filter correlation unit may, for example, a so-called matched filter mechanism may be implemented using a cross-correlation between the wanted and the received signal is performed.

In a further refinement of this embodiment, the filter correlation unit is designed to correlate the angle signals with a sinusoidal and with a cosinusoidal filter-signal sequence. Especially with a cosinusoidal filter-signal, i .e. if a cosinusoidal signal the transmitter is expected, the amount of calculation compared to a matched filter process can be significantly reduced if the transmitter signal into a sine and a cosine component is decomposed. In this case suffices in place of the cross-correlation with a simple multiplication of the sine and the cosine component of the pattern or filter signal with subsequent magnitude formation and moving average filtering.

In other embodiments, the signal processing device a search device according to the invention comprises an autocorrelation unit adapted to detect in signals stored by autocorrelation periodic signal components. If the signals of several transmitters received, the transmitter signals, the transmitter can mutually overlap and also obliterate one another. Because no two devices always have slightly different from each repetition and / or duty cycles, however, an association of the respective received signal to the one or the other transmitter is in principle possible. In the superposition of signals of several transmitters is the sum of several periodically switched on and off signals. Therefore is the autocorrelation function to detect the periodic components of this summed signal. For example, from the measured reception field strengths by threshold decision an on / off function are formed, the autocorrelation function contains spectral lines at the frequencies. Thus, separation of the signals from several transmitters by providing an autocorrelation unit in the detector is possible.

In further embodiments, the search device according to the invention, the autocorrelation unit of a filter correlation unit is connected downstream. This results in the construction of the search device designed particularly advantageous because initially all detectable (possibly weak) transmitter signals can be identified and then easily convert these signals can be assigned to different transmitters.

In further embodiments, the search antenna of the search device according to the invention comprises a ferrite antenna, preferably with cosinusoidal directional characteristic. Ferrite antennas are particularly suitable because of their high directivity for transmitter localization. A cosinusoidal directional characteristic allows, for example, a configuration of the filter correlation unit as indicated above, the angle signals are correlated with a sinusoidal and with a cosinusoidal filter-signal sequence.

In further embodiments of the invention, the detector comprises a transmitter for transmitting the transmitter signals, the transmitter signals are preferably individualized by a transmitter identification. This group functions can be realized, in which a plurality of transmitters at least one can be identified by its individualized identifier, for example, the group leader of a group of skiers.

In certain other embodiments of the invention, the signal processing means for generating processing signals is formed, assign a transmitter search angle a station identification, a transmitter is configured such that the transmitter signals on this channel can be individually characterized over transmitter signals other stations. This allows the user of the search device according to the invention are provided with the option to in an advantageously simple way to display a plurality of detected from a transmitter in a prominent manner.

A method for locating a transmitter, in particular a radio station in an avalanche has, conventionally the following steps:<ul><li>to scan a search area, a search device is swung by a user in an angular range of search angles that covers the search area,</li><li>Transmitter signals that are broadcast from the transmitter are received from current search directions by a search antenna of the search device,</li><li>Processing signals are generated from the transmitter signals and</li><li>Result signals that represent the processed signals are output to the user.</li></ul>

According to such a method is further developed in such a way that the sensor signals that affect the Earth's magnetic field, are displayed as a processing signal by result signals to users and any search direction, a fixed search angle is assigned relative to the Earth's magnetic field. In order for the Earth's magnetic field is used as a fixed reference coordinate system, and it is the association of the measured transmitter signal of a transmitter possible at any time to a fixed search angle.

In preferred embodiments of the inventive method are measured for the assignment of search direction and angle field strength components of the geomagnetic field in three mutually perpendicular directions. Thus, the solid angle of the device can be determined relative to the field lines.

In other preferred embodiments of the inventive method, the inclinations of the search device can be measured from the horizontal plane and corrects the sensor signals accordingly. Thus it can be determined exactly advantageous point of the compass.

In further embodiments of the inventive process angle signals, each indicating a received signal strength at a search angle, generated from the transmitter signals and the assignment of search direction and search angle. After generation of the angle signals the application of signal processing mechanisms on these signals is advantageously possible, which allows the determination of the transmitter site in a particularly simple and reliable manner.

In further embodiments of the method according to the invention is a transmitter search angle in which the transmitter is located, calculated from the angle signals and output a result signal representing the transmitter search angle. This enables the location of the transmitter can be determined, since the determination of the distance between transmitter and detector by conventional methods is easily possible. A determination of the transmitter site by ear is not required. The transmitter search angle can be determined by one or more times swiveling the search device according to the invention, even if the device has already been back in a completely different direction.

In another embodiment of the invention, the transmitter search angle of at least two, in particular, determined at least three angle signals. In clocked transmitter signals of a transmitter is at a random swiveling movement is often the case that the channel is in a silent period, when the search appliance is held toward maximum or minimum field strength. The sequence of angle signals, ie, the function of the received signal strength over the search angle is, therefore, generally present only in sections. Therefore, the inventive method is advantageously configured to extrapolate from the intermediate values ​​maximum and minimum. For this purpose, in principle any two points of the field strength curve (ie two angle signals) sufficient when the directivity of the search antenna is known. For a robust approximation to the use of at least three angle signals is advantageous.

In further embodiments of the aforementioned embodiments, an estimated angle-signal sequence is calculated by the method of least squares from the angle signals and the scanning angle is determined from the maximum of the estimated angle-signal sequence. For the present, in sections follow the angle signals, the parameters determining the entire waveform can be estimated using the method of least squares. It can easily be the estimated angle-signal sequence are calculated, as previously stated above.

In further embodiments, this embodiment angle signals are weighted differently, especially according to the time that has elapsed since receipt of the angle signals underlying transmitter signals when calculating the estimated angle-signal sequence. When applying the method of least squares estimation can be constantly improved by consulting new readings. This quickly results even at great distances from the victim and correspondingly weak transmitter signal a relatively accurate location estimate. On the other hand can be older by a corresponding weighting in proportion to the actual measurements and the angle signals determined therefrom suppress cracking or excessive instability of the calculated transmitter search angle can be reliably.

In further embodiments of the inventive method estimated transmitter signals are determined by correlation of transmitter signals with predefined filter signals and determines angle signals from the estimated transmitter signals. If a cross correlation between the filter signals and the transmitter signals performed which detect weak signals from a transmitter is made possible, which. Is located for example at a great distance from the detector, and this corresponds to detecting a signal of known form in the noise.

In another aspect of this embodiment each have a sinusoidal and a cosinusoidal is determined for the determination of the transmitter signal from random noise by correlating the received transmitter signals with a sinusoidal and with a cosinusoidal filter-signal sequence. In principle, the above-mentioned cross-correlation may be performed by means of a matched filter mechanism. The drawback of the matched filter, however, is a high computational effort. This is because the pattern represented by the filter function signals must be compared in all possible phase positions of the sequence of received transmitter signals. This computing effort can be reduced considerably, if the sequence of transmitter signals into a sine and a cosine component is decomposed.

In another aspect of this embodiment receive field strengths of the signals of the estimated transmitter signal sequence from the summation of the (if necessary, downconverted) received signal sequence of the products are determined with a sine and a cosinusoidal. The argument (angle) of the complex number formed by the above-mentioned sine and cosine component describes the phase position of the received signal relative to the cosine pattern function, while the amount of the complex number is a measure of the reception field strength.

In preferred embodiments of the inventive method for the detection of multiple transmitters, a periodic signal component of stored transmitter signals or processing signals, in particular estimated transmitter signals detected by autocorrelation. If the signals are several avalanche received, the transmitter signals, the transmitter can mutually overlap and also obliterate one another. Since two transmitters always exhibit slightly different from each repetition and / or duty cycles, however, an association of the respective received signal to the one or the other transmitter is in principle possible. In the superposition of signals of several transmitters is the sum of several periodically switched on and off signals. Therefore is the autocorrelation function to detect the periodic components of this summed signal. For example, from the measured reception field strengths by threshold decision an on / off function are formed, the autocorrelation function contains spectral lines at the frequencies. Thus, separation of the signals of multiple channels is possible. By averaging the autocorrelation function over several observation periods, dominant periodic components can be determined very reliably relatively independent of the particular alignment of the transmitter to the receiver.

In one aspect of this embodiment, a detected periodic signal component, which can be associated with a transmitter, hidden from the transmitter signals or processing signals to detect other periodic signal components. Due to noise and inaccuracies the periodic components of weaker reception signals are often obscured. To detect these proportions, it is advantageous if the signal components that can be assigned to a dominant received signal hidden (set to zero) are.

In further embodiments of the method the transmitter signals a transmitter over the transmitter signals other stations are individualized by a transmitter identification and there are processing signals generated that assign a transmitter search angle this sender identification. This group functions can be realized, in which a plurality of transmitters at least one is optional identifiable by its individualized identifier, for example, the group leader of a group of skiers.

Other aspects, advantages and expediencies of the invention will become apparent from the following description of an embodiment of the invention with reference to the accompanying figures, of which:<dl id="dl0001"><dt>Fig. 1</dt><dd>an embodiment of a search device according to the invention;</dd><dt>Fig. 2a, 2b</dt><dd>each have a view of the display of the search device of FIG. 1;</dd><dt>Fig. 3</dt><dd>in schematic form a functional block diagram of the search device in FIG. 1.</dd></dl>

In the figures, like reference numerals are used for identical and functionally identical elements.

FIG. 1 shows an embodiment of an inventively embodied search device 1 for use as an avalanche transceiver search device (avalanche transceiver). The communication with the user via an illuminated display 10 and two control buttons 12, 13. The display 10 allows the graphical display of the position of one or more Spilled relative to its own location. The device 1 also has a speaker 14 for outputting a synthetically generated search tone to the user as an acoustic feedback as well as a LED 15, as is known for conventional devices. The speaker 14 and the red LED 15 permit conventional search even without use of the graphical display on the display 10th

As shown 2a in detail in Fig., The display of the display 10 is divided into a coordinate field 16 to true to scale the position of the located transmitters of buried, a status bar 18 with the respective key information and labeling fields 20 for the two control buttons 12th

The device 1 is designed as a combined search and transmission unit. The housing has the shape of a foldable mobile phone. The hinge is indicated in Fig. 1 by a dashed line 21.. the device 1 is in the search mode is automatically switched back by closing the device to transmit mode. This is achieved in an advantageous manner a failback, as, eg. In the case of a second avalanche, is called for in the standards.

The device 1 is equipped with a non-visible to the outside antenna for transmitting and searching on a search frequency of 457 kHz. The specified frequency for avalanche victims search equipment standardized (EN 282). An automatic location of a buried occurs from the natural pivotal movement of the seekers or user. According to the invention, however, no manual bearing as in conventional devices is needed. In addition, the illustrated device 1 has a bearing mode to focus on a selected victim.

A search process works from so that the seeker back the device 1 after switching from transmit to search mode a few times to about 180 degrees swings back and forth. The achievable DF or search accuracy is initially about ± 10 degrees. When swinging all transmitting or transmitter signals of the transmitters of buried subjects are detected, which are in reach. The range of the device is about 80 m. The transmitters can be conventional transceivers, or identical to the device 1 device. A manual bearing, that is holding the device 1 in the direction of the strongest signal is not required.

The channels reported 22 displays direction and distance on the display 10, where the full scale representation of the distance of the transmitter 22 from the seeker (in the center of the coordinate field 16, ie, the reticle 23) is specified by the distances above 24 meters.

The seeker can now by request of the victim, which is to be found first, and pressing the 12 "FINDING" key focus on these and other channels 22 Hide. During the search, the distances above 24 and position information 22 are continuously adapted to the current position of the searcher.

The target search in the vicinity can be supported by the red LED 15th Moreover, for precise pinpointing a zoom function can be activated in the display 10 (not shown). When approaching the seeker to a transmitter site 22, ie the presumed point of a buried sun, a circle on the display 10 is shown, which is concentric with the sun point 22 and decreases concentrically on further approach. Experience has shown that an insertion of the circle from a distance of three meters is beneficial, but the overlay can also be done even at larger or only at shorter distances. Instead of a circle, a square symbol, or the like could be used.

By means of the search device according to the invention can be easily determined the exact burial. To this end, the seeker brings the detected transmitter 22 (the point where the person suspected victim) with the center of the crosshairs 23, so that the seeker is (the position of the seeker) cover vertically above the victim. The distance information 24 are then at the burial. In known detectors to determine the burial depth is only indirectly and with greater yields burial unreliable values, because the display often have a diameter of up to several meters remains the same with greater depth and the depth of no more precise details are possible.

Is a Spilled found and rescued, the searcher removes the bearing and is dedicated to the next subject.

The search device 1 is equipped with a motion sensor (not shown). This detects whether the device 1 is moved. If the device is in any mode other than the transmission mode, and the device does not move over a period of 90 seconds, will be automatically switched to the transmit mode. Thereby, the above-mentioned failback is also triggered safe when the seeker due to avalanche or the like surprising event has no opportunity for closing the search appliance.

The detector 1 has in the exemplary embodiment outlined here next to the search box on other programs that can be selected via the button to reach the 13 main menu. This includes an electronic compass, a temperature display and tilt measurement for assessing the danger of avalanches, an indication of battery status and time remaining display for transmitting and search operation. When the battery is low, regardless of the operating mode is a warning.

Although the standard allows for security principle no additional functions (compass, temperature display, tilt measurement). However, search apparatus of the invention requires eg. The inclinometers to its operability. Then only, care must be taken to ensure that the display of data in addition gained no power consumption is increased so that the safety of the use is no longer guaranteed. Therefore, a safety circuit is in the detector 1 is provided (not shown), which switches off the display of additional functions when the battery capacity falls below 50% of maximum. Thus, the standard requirements are met to the reliability of the device.

In any other detection equipment according to the invention are only a few or none of these additional functions before; Thus, even a safety circuit of the kind described above are eliminated.

Furthermore, a quick guide for the device and configuration screens and Konfigurationseinstellmöglichkeiten for language and display lighting can be reached via the main menu of the search unit 1.

The integrated sensors which are described more fully below, the device 1 can determine at any time, in which direction the seeker it just keeps. So the position of the located transmitter of burials can be displayed at any time correctly relative to its own position.

From the Fig. 2a illustrated display is intuitively clear that the Spilled shown highlighted in the coordinate field 16 26 exactly at 30m in the direction in which the device 1 is held. The lying directly ahead at the next - highlighted illustrated - Spilled by pressing the button 12 ( "FINDING") are selected for further search. As shown in Fig. 2b, so that the information is reduced in the display 10 on the data of the targeted victim 26th The speaker 14 (see. FIG. 1) are only in distance-dependent manner the search tone of the targeted victim 26 again. The bearing can be canceled at any time by pressing the 13 button ( "ALL"). Multiple search is also possible for up to six burials.

The technical realization of the detector 1 is performed in principle so that the received 457- kHz signals are digitized and processed with a powerful microprocessor. Algorithms of digital signal processing allow search sounds, that even then filter out transmitter signals from the noise when they already lie below the threshold sense of human hearing. This enables a conventional, analog operating devices comparable scope.

From the received signals, the positions of the buried subjects are calculated. The algorithms used are robust against individual faults or measurement error. Since over the entire search phase, the positions are continuously recalculated, the accuracy of the estimated position of the victim improves rapidly with time.

In Fig. 3, the functional construction of the apparatus 1 of FIG. 1 is shown schematically. In addition to the receiver 28 with the antenna search and mixing stage for the search tone, a sensor 30 for the earth's magnetic field, which a sensor signal for each rotational degree of freedom (X, Y, vertical) to write, as well as inclination sensors 32 for the two pivot axes are provided. In addition, another sensor 34 for one of the above Additional features of the device, the temperature measurement, located.

The microprocessor-controlled sample manager 36 performs the current sample to the correct destination and selects the channel for the next sample from. The timing is designed so that the maximum possible sampling essentially stands for the sampling of the received, ie transmitter signals. For the sampling of the sensor data, the received signal is about hidden every 32nd time slot and, instead of the sensor channels for temperature, magnetic field and inclination is read.

In angle estimation module 38 the spatial position of the Earth's magnetic field is accurately determined from the samples of the magnetic sensor 30 and the tilt sensors 32nd Such methods are known in the art per se and are therefore not described further. By using these sensors 30, 32 is according to the invention each direction in which the search device 1 is held, assigned φ with respect to the measured magnetic field vector μ a fixed search angle.

The sin / cos correlator 40 is provided for the detection of transmitter signals to the sensitivity limit. Basically, the task is a

to even locate buried in far away as possible. This corresponds to detecting a signal of known form in noise.

The discovery of such a search tone in noise is - in the sense of a hypothesis test - ideally with a "matched filter" possible, which basically a cross-correlation between the sought and the received signal is carried out.

The matched filter has an impulse response exactly along the time axis mirrored unknown function. Winning the matched filter is due to the fact that useful signal components are constructively added by the impulse response while interfering signal add up in terms of performance.

The drawback of the matched filter is the high computational costs. This is because the pattern function must be compared in all possible phase positions with the consequence of received, ie transmitter signals.

From the transmitter signal sequence is known that it is a cosine signal sequence with a constant frequency. Each arbitrarily scaled and phase shifted sine wave can be divided into a cosine and sine disassemble a share. The power of the wanted signal is the sum of the powers of sine and Kosinusanteil. Therefore, it is sufficient to multiply the transmitter-signal sequence with a cosine and a sine filter-signal sequence, that is to divide the sequence of the transmitter signals into a sine and a cosine component. The argument (angle) of the complex number formed by sine and cosine component describes the phase position of the received, ie transmitter signal sequence in relation to the cosine pattern function, while the amount of the complex number is a measure of the reception field strength.

System In theory, the work in this manner, sin / cos correlator 40, demodulation of the search tone to baseband (Multiplikati on with sin or cos) and subsequent low-pass filtering to suppress the image frequencies at twice the signal frequency. An important advantage of the sin / cos correlator 40 is so that it can be constructed easily and conserve resources. Compared to a matched filter detection performance is worse by 3 dB. Values ​​obtained - In the RSS module 42 from the output values ​​a (estimated amplitude value of the sine component) and b (amplitude estimate of the cosine) of the correlator 40 by square averaging RSS ( "Received Signal Strength") are. The AKF-module 44 then computes the autocorrelation function (AKF) of the RSS values. The output of the ACF module 44 serves as a basis for separation of the signal components for multiple simultaneously active transmitters.

The search for trapped designed then special difficult when simultaneously the signals of several Spilled received. The transmitter signals of the transmitters may interfere with each other and also obliterate one another. Because no two devices always have slightly different from each repetition and / or duty cycles, however, an association of the respective received signal to the one or the other transmitter is in principle possible.

In the superposition of signals of several transmitters is the sum of several periodically and switched signals. Basically therefore suitable an autocorrelation function to detect the periodic components of this summed signal.

In the simplest case from the measured field strength values ​​by threshold decision an on / off function formed whose autocorrelation function should contain spectral lines at the frequencies. The disadvantage of this method is that even at low field strengths or imperfect alignment of the receiving antenna, the on / off times can be determined only insufficiently accurate to the transmitter. Through these inaccuracies, the spectral lines of the autocorrelation function are smeared, that is out of focus, and quickly become unusable.

Just as in the ideal one-off function, the information on the periodicity are naturally present in the analog field strength function. This is that is obtained as the amount of output of the sin / cos correlator 40, as output of the RSS module 42nd By averaging the autocorrelation function over several observation periods, dominant periodic components can be determined very reliably relatively independent of the particular alignment of the transmitter to the receiver.

Due to noise and inaccuracies the periodic components of weaker reception signals are often obscured. To detect these shares, are signal components, which can be ascribed to a dominant received signal, hidden (set to zero).

The assignment of individual signal portions to different transmitters is carried out by heuristic segmentation segmentation module 46th Given that signal elements are essentially determined by threshold decision that contribute to the maximum of the AKF. The signal elements thus obtained are optionally separated by analysis of jumps in the correlation values ​​again and assigned to different channels. A signal element can, for example, starting from the left and right border in two separate areas on the edges and a - be divided overlay area in the middle - not usable for location estimation. Segmentation cracks and discontinuities can be used in the sine and cosine correlation values.

In location estimation module 48, the location of at least one station being received is determined. The distance of the transmitter can be determined reliably in a conventional manner by application of a power law to the measured or calculated field strength. At the same time takes place in the module 48, the assignment of the search angle according to the invention derived from the sensor data φ σ to the company resulting from the current measured transmitter signals processing signals indicating the instantaneous reception field strength of a transmitter.

The ferrite receiving antenna used in the receiver unit 28 has a cosinusoidal directional characteristic. In a stationary transmitter, the received field strength changes accordingly with the cosine of the double angle search. If the unit is tilted by searchers while looking back and forth, so changing the angle continuously, can be formed as a function of the search angle φ in the site estimation module 48 thus easily σ the field strength. For all angle signal elements of a recording interval (from which exactly one ACF was calculated), is by linking to the search angles φ the transmitter search angle and thus the location of the transmitter appreciated. The coordinates are determined from consecutive recording intervals for the same transmitter can be continuously improved by a weighted averaging.

Due to the timing of the search tone, ie the received transmitter signal sequence, the field strength function, ie the sequence of angle signals σ (φ), each indicating a received signal strength at a search angle, generally present only in sections. From the available sections, however, the parameters determining the entire waveform can be estimated using the method of least squares. It can be calculated in a simple manner angle and distance of the transmitter.

In fault-free case could be calculated as a result of estimated angle signals from the field strength during the station received signal sequence of the entire field strength course. To calculate sufficed any two points of the transmitter-signal sequence. In practice, the received signal is, however, more or less noisy. The data used for the approximation of two points may then be randomly heavily corrupted by noise samples, so that the parameters of the actual angle signal sequence greatly erroneously estimated. In order to achieve a trouble-robust estimation, all available points of the received field intensity profile or the transmitter signal sequence should be included and the required parameters are optimized so that the total deviation of the calculated course of the estimated angle-signal sequence from the portion of the sequence of determined from the transmitter signals and search angles angle signals minimal becomes.

When applying the method of least squares estimation can be constantly improved by consulting new readings. Firstly, it easily yields even at great distances from the victim and correspondingly weak search or received signal a relatively accurate location estimate. On the other hand can be older by a corresponding weighting in relation to the current values ​​of the measured or calculated, search angle signals suppress cracking or excessive instability of the detected transmitter search angle can be reliably.

Thus, a reliable determination of the position of the transmitter is possible with an adequate number of measurements. This is especially true if the maximum itself can not be detected because just, this is at times, which shows the searching device in the direction of the transmitter in the pulse pauses. The data of the real received signal provide guidance for the necessary number of samples for a sufficiently accurate determination.

Also object of the location estimation is to solve the problem, two of the field strength differences or more consecutive recording intervals dissolve the 180 degree ambiguity the angle estimate and allocate the transmitter to the front (in the direction of movement) or rear (against the movement direction) half-plane.

This is the location of a buried subject, in particular the transmitter search angle, and then completely and reliably predictable when its transmitter is at the time at which the unit 1 of the seeker shows in his direction, straight into the intermission. This is achieved with an inventive design search apparatus comprising only a single search antenna and can therefore be correspondingly easier and cheaper (of course, the use of multiple antennas in a search device according to the invention is also possible).

The determined location of a transmitter is then placed on the display 10 for display, as described above with reference to FIGS. 1, 2a and 2b.

The presentation of the functions of the search appliance by way of example the invention described herein is based on modules, which are drawn in FIG. 3 as separate units. These units may be present in the search device in the form of software, firmware and / or hardware. Preferably, the modules are in the form of software before on a microprocessor / DSP. For a full-featured search device such as that illustrated with reference to the figures, a processor with 30 MIPS processing power and 8 KB of memory would be suitable.

Numerous variations of the search device described as an example here are conceivable. So may be designed to separate the signal components of several transmitters, an inventive device without ACF module or module. Such a device can be used in situations where only one transmitter must be located. An example of this is a group of skiers on a secured door, in the discovery of the group leader is made possible by the detectors of the group members, and only the sender of the conductor in the transmission mode is.

It can also be formed with weak search or received signals, an inventive detector without module for carrying out the cross-correlation of a filter signal. Then weak signals are noise no longer detectable, the sensitivity of the search device is correspondingly reduced. However, then the resources of the device (available memory, processor processing capacity) are available for other functions, eg., The ACF module be configured to separate a large number of TV channels from each other. Also, a functional poorer device with the same battery capacity have a prolonged period of operation, as when a smaller processor is used.

It is conceivable to combine an inventive detector with a GPS system. The GPS system provides a lifelike representation of the terrain. The position of the seeker and detected by the detector transmitter locations, ie the presumed Liege points of burials are superimposed on the representation of the GPS system. Such a system allows the seeker the position of the sun based on any existing point striking terrain points intuitively, that quickly capture, so that he can visit the sun point with the least possible delay.

Alternatively or additionally, the search device can be combined with a voice control, as is known for motor vehicles as in GPS systems. Here the seeker receives voice instructions, in the form of a voice generated by the detector. This enables the seeker to concentrate on the terrain.

An inventive search apparatus may further be combined with a camera such as this is known for mobile phones. Here, the power consumed by the camera view area is reproduced on the display of the search device advantageously. The transmitter locations detected are superimposed on the terrain. The view on the display is broadly in line with the view that has the seekers of its surroundings. Thus, the orientation of the seeker is facilitated, in particular in form-rich terrain.

A combination of a search device according to the invention with a GPS system and camera is possible. This GPS system and camera would cooperate to achieve a detailed outline and rich representation of the terrain.

Instead only avalanche transceiver search unit, an inventively constituted detector also advantageously be used for other applications. As an example, a group of skiers called, which are based on their group leader, for example. In poor visibility or otherwise confusing situation. All participants have transmitter / detectors. The unit of the conductor has a transmitter whose signal transmitter is provided with an individual transmitter identification. The detectors of the group participants are designed for the evaluation of the received transmitter ID so that the located stations of the conductor can be identified among the plurality of the located transmitters. The display of search devices of the participants identifies the location of the group leader by specifying the identifier. In a further development of this process all the channels of a group by transmitter identifiers are customizable.

Although the transfer of station names on the standardized signal at 457 kHz is not provided. However, a second transmitter may be provided in addition to the otherwise standard compliant transmitter in a transmitter which emits signals with transmitter identifications.

Moreover, the scope of the invention, which is given solely by the following claims, conceivable by craftsmanship action many other embodiments.

LIST OF REFERENCE NUMBERS

<dl id="dl0002" compact="compact"><dt>1</dt><dd>detector</dd><dt>10</dt><dd>display</dd><dt>12, 13</dt><dd>control buttons</dd><dt>14</dt><dd>speaker</dd><dt>15</dt><dd>LED</dd><dt>16</dt><dd>coordinate field</dd><dt>18</dt><dd>status line</dd><dt>20</dt><dd>Labelling field for control buttons</dd><dt>21</dt><dd>Klappscharnier</dd><dt>22</dt><dd>Symbol intercepted transmitter in the coordinate field 16</dd><dt>23</dt><dd>crosshairs</dd><dt>24</dt><dd>Distances in the coordinate field 16</dd><dt>26</dt><dd>highlighted shown of detected stations</dd><dt>28</dt><dd>Receiver with search antenna</dd><dt>30</dt><dd>Sensor for the Earth's magnetic field</dd><dt>32</dt><dd>inclinometers</dd><dt>34</dt><dd>temperature sensor </dd><dt>36</dt><dd>Sample Manager</dd><dt>38</dt><dd>Angle estimation module</dd><dt>40</dt><dd>Sin / cos correlator</dd><dt>42</dt><dd>RSS module</dd><dt>44</dt><dd>AKF module</dd><dt>46</dt><dd>Segmentation module for heuristic segmentation</dd><dt>48</dt><dd>Location estimation module</dd><dt>a</dt><dd>Amplitude estimate of the cosine</dd><dt>b</dt><dd>Amplitude estimate of the sinusoidal component</dd><dt>r</dt><dd>Received, ie transmitter signal</dd><dt>R</dt><dd>Output of the RSS module</dd><dt>μ</dt><dd>magnetic field vector</dd><dt>φ</dt><dd>search angle</dd><dt>σ</dt><dd>detected reception field strength of a transmitter</dd></dl>