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 to scan a search area by the locator a user is pivoted in an angular range that covers the search area.

Avalanche transceiver search devices operate with an unmodulated transmit signal at 457 kHz. All skiers in a group turn their devices in normal operation Broadcasting. If a part of the group buried in an avalanche, the switch other people using their devices to receive and try the victim of the transmitted signal to locate.

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

produce for the detection by ear (or maximum / minimum field strength) conventional devices from the transmission signal at 457 kHz by down-mixing a audible search tone at a frequency of about 2 kHz. Since the built-in antenna, a has pronounced directivity, by rotating the receiving device and Search the volume maximum or minimum, the direction of maximum field strength to determine the buried transmitter. This technique requires the Seekers high concentration, exercise, and just at greater distances small Ambient noise.

To simplify the seeker even without exercise and stress situations the search, were devices with multiple, mutually perpendicular antennas arranged developed. By switching between these antennas, the receive direction to determine the transmission signal.

This method has a number of disadvantages in practice. influence to a the antennas to each other, even if they are turned off so that the receiver sensitivity the device overall suffers. In particular, a direction determination at great distances over 50 meters almost impossible, the thus obtained Direction indicator therefore not be used. Secondly, this technique is very so that the direction indicator optimal sensitive to interference, under no Conditions varies widely.

A particular challenge for the seeker is when he signals several avalanche receives simultaneously. The localization by ear requires here extraordinary amount of exercise and a cumbersome search strategy.

The object of the invention is to specify a generic search device, which the position of at least one victim to reliable and cheap Way automatically determined.

This object is, and by a detector with the features of claim 1 a Locating process achieved with the features of claim 17.

An apparatus for searching (at least) a transmitter, especially an avalanche transceiver search unit, wherein to scan a search area by the locator a user is pivoted in an angular range of search angles that the Search area covered, has conventionally include:<ul><li>a search antenna for receiving transmitter signals, the current from the transmitter Search directions are broadcast, </li><li>a signal processing unit for generating processing signals from the Transmitter signals and</li><li>an output unit, which are supplied to the processing signals, for outputting Result signals that represent the processed signals to the user.</li></ul>

According to the invention, such a search device further comprises a magnetic field sensor on, the sensor signals the Earth's magnetic field corresponding to the signal processing means outputs, which are supplied as a processing signal of the output unit and each Search direction a fixed search angle, relative to the earth's magnetic field, assign.

An essential idea of ​​the invention is that a search device that the solves above object, like a radar working ideally and the antenna ever would to an angular range, for example. 180 degree turn. Because it is known, the angle at which the antenna is straight, may at any time a received associated signal with the respective field strength the current angle of the antenna will. This is so in practice, of course not feasible. After all, but the rotation of 180 degrees is achieved in that the person seeking the device keeps 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 what angle to an external reference coordinate system the device is at a given time.

In principle, it is conceivable to search information on the current angle by the to obtain evaluation of the signals of acceleration sensors or rotation sensors. In practice, perform initial value problems and the constant acceleration of gravity this large errors.

Also could about the search angle may from the evaluation the GPS signal can be obtained. Are contrasted by the relatively high cost of a GPS Receiver and - for rescue applications - generally insufficient availability adequate GPS signals contrary.

According to the invention, the earth's magnetic field as such, fixed and permanently available Reference coordinate system used. Thus, at any time the assignment the received transmitter signal of a transmitter at a fixed search angle possible.

In a preferred embodiment of the search device according to the invention are the Magnetic field sensor three Earth's magnetic field corresponding sensor signals to the signal processing means out. Thus, the solid angle of the device relative to the leaves Field lines determine where the field strength of the geomagnetic field components in three vertical axes are measured.

In addition, magnetic field sensors are cheaper with an accuracy of 1 degree So that search device according to the invention manufactured as a GPS receiver cost-effective can be.

In a further embodiment, inclination sensors are provided, the sensor signals to output the signal processing device, which based the location of the search device represent a horizontal plane. From the sensor signals from the inclinometers can be corrected advantageously, the sensor signals of the magnetic field sensor that relative position of the search device to Earth's magnetic field very accurately and independently of the horizontal position of the search device can be determined.

In further embodiments, the search device according to the invention is the signal processing device adapted to from the transmitter signals and the sensor signals generate angle signals a a reception field strength as a function of Search angle represent. The use of signal-processing mechanisms on Angle signals according to the invention enables in a particularly simple and reliable Thus, the determination of the transmitter site.

In a further embodiment in particular, the aforementioned embodiment is the Signal processing means for calculating a channel scan angle, in which the Transmitter is formed based on the angle signals. In this way, by the search appliance 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 the transmitter site by ear is not required. The transmitter search angle can after single or repeated swiveling of the search device according to the invention be determined, even if the device is already again in a completely different Direction shows.

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

One problem with transmitters to locate Spilled is that the transmitter signal the transmitter is clocked. With a random pivoting movement it is so often happen that the channel is in a silent period when the detector toward maximum or minimum field strength (during the times at which the Transmitter transmits) is held. The sequence of angle signals, ie, the function of Receive field strength above the search angle, therefore, is generally only in sections present. It is advantageous, therefore, the search unit, an algorithm implemented to extrapolate the maximum and minimum of the intermediate values. in the Principle for this purpose are any two points of the field strength curve (ie two Angle signals) required when the directional characteristic of the search antenna known is.

These are the - as before for the search angle and subsequently for the field strength described - obtained images (Time -&gt; search angle) and (Time -&gt; field strength) in a mapping (search angle -&gt; 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 image - through (search angle&gt; field strength) Applying the method of least square error performed. this makes possible continual 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 designed for graphical output of result signals that the transmitter search angle represent, and in particular a display for graphically displaying the Transmitter site included in the search area. This advantageously fast, allows intuitive grasp of the transmitter site by the user.

In further embodiments, the search device according to the invention comprises the signal processing device a filter correlation unit that is configured to angle signals by correlation of transmitter signals (received signal and down blended Received signal) to detect with predetermined pattern or filter signals. hereby allowing the detection of weak signals from a transmitter, the example itself. in great distance from the detector is. This corresponds to detecting a signal of known form in noise. On the filter correlation unit can eg. 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 aspect of this embodiment, the filter correlation unit formed to the angle signals with a sinusoidal and with a cosinusoidal correlating filter burst. Especially with a cosinusoidal filter-signal, i .e. if one cosine signal it is expected the computational effort can be compared to a matched filter method significantly reduced if the transmitter signal is decomposed into a sine and a cosine component. In this case, sufficient in place of the cross-correlation with a simple multiplication of the sine and the Cosine of the pattern or filter signal with subsequent value formation and moving average filtering.

In further embodiments, the signal processing device of an inventive Search device in an auto-correlation unit, which is adapted to in stored signals to be detected by autocorrelation periodic signal components. If the signals of several transmitters received, the transmitter signals the superimpose stations mutually and also obliterate one another. Because no two devices always easily have mutually different repetition rates and / or duty cycle, is However, in principle, an assignment of each received signal to one or other transmitter. In the superposition of signals of several transmitters is is the sum of several periodically switched on and off signals. Therefore is the autocorrelation function to the periodic components of this summed signal to recognize. 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, a Separation of the signals of several transmitters by providing an autocorrelation unit in Detector possible.

In further embodiments, the search device according to the invention is the autocorrelation unit a filter correlation unit downstream. This is designed the structure the search device 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 comprises the search antenna of the search device according to the invention a ferrite antenna, preferably with cosinusoidal directional characteristic. Ferrite Antenna are because of their high directivity for transmitter localization particularly suitable. A cosinusoidal directional characteristic allows, for example, an education the filter correlation unit as indicated above, wherein the angle signals correlated with a sinusoidal and with a cosinusoidal filter-signal sequence will.

In further embodiments of the invention, the detector includes a transmitter for Sending transmitter signals, wherein the transmitter signals, preferably by a transmitter identification are individualized. This allows group functions realized are experiencing from a plurality of transmitters at least one of its is individualized identifier identifiable, for example, the group leader of a Group of skiers.

In certain further embodiments of the invention, the signal processing means is designed to generate processing signals that a transmitter search angle assign a transmitter identifier, wherein a channel is formed such that Transmitter signals of this transmitter individualisierbar opposite transmitter signals other stations are. This allows the user of the search device according to the invention advantageously easily be provided the option to one of a plurality To display of detected stations in emphasized manner.

A method for locating a transmitter, in particular a radio station in an avalanche Victim has, conventionally the following steps:<ul><li>to scan a search area is a search device by a user in a Angle range of search angles swiveled, which covers the area of ​​search,</li><li>Transmitter signals from the broadcaster, are from current search directions received 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 sent to the User output.</li></ul>

According to the invention such a method is further developed in such a way that Sensor signals which affect the Earth's magnetic field, as a processing signal by will result signals displayed to users and any search direction, a fixed Search angle is assigned relative to the Earth's magnetic field. This is the earth's magnetic field used as a fixed reference coordinate system, and it is at any time the assignment the measured transmitter signal of a transmitter at a fixed search angle possible.

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

In further preferred embodiments of the method according to the invention the inclinations of the search device can be measured from the horizontal plane and the Sensor signals corrected accordingly. Thus, advantageously the direction exactly be determined.

In further embodiments of the inventive process angle signals, each having a received signal strength at a Suchwink specify el, from the generates transmitter signals and the assignment of search direction and search angle. After Generating the angle signals is advantageous applying signal processing Mechanisms to these signals possible, which in a particularly simple and reliable Thus, the determination of the transmitter situation allows.

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

In a further embodiment of the invention, the transmitter search angle of at least is two, in particular at least three, determine angle signals. In clocked transmitter signals a transmitter, it is at a random pivotal movement often the case that the station is just in a transmission pause when the detector maximum towards or minimum field strength is maintained. The sequence of angle signals, ie, Function of the received signal strength over the search angle, therefore, is generally only partially present. It is therefore advantageous method of the invention configured to from the intermediate values ​​of the maximum and minimum extrapolate. For this purpose, in principle any two points of the field strength curve (d. h. two angle signals) is sufficient, if the directivity of the search antenna is known. For a robust approximation is the use of at least three Angle signals advantageous.

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

In further embodiments, this embodiment will be in the calculation of Estimated angle-signal sequence angle signals weighted differently, in particular in accordance with of time, the underlying since reception of the transmitter signals the angle signals has passed. When applying the method of least squares, the Estimate the constant improvement by attraction of new metrics. Thereby, even at a great distance from the victim and in accordance with weak transmitter signal quickly, a relatively accurate location estimate. On the other hand leaves by an appropriate weighting of elderly in relation to the current Measured values ​​or the angle signals determined therefrom cracking or excessive suppress instability of the calculated transmitter search angle can be reliably.

In further embodiments of the inventive method are estimated transmitter signals by correlation of transmitter signals with predefined filter signals determined and calculated angle signals from the estimated transmitter signals. A cross-correlation carried out between the filter signals and the transmitter signals, the Detect weak signals from a transmitter enables the example itself. In large Distance is from search unit, which should be accompanied to detecting a signal corresponds to a known form in noise.

In a further aspect of this embodiment is to determine the Transmitter signal from random noise by correlating the received transmitter signals with a sinusoidal and with a cosinusoidal filter-signal sequence are each a Sine and a cosinusoidal determined. In principle, the above-mentioned cross-correlation be performed by means of a matched filter mechanism. The disadvantage the matched filter, however, is a high computational effort. This is because the by the filter signals represented pattern function in all possible phase positions with the sequence of received transmitter signals to be compared. This computational effort can be significantly reduced when the result of the transmitter signals into a sine and a cosine component is decomposed.

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

In preferred embodiments of the inventive method for detecting from multiple transmitters, a periodic signal component of stored transmitter signals or processing signals, in particular estimated transmitter signals by autocorrelation determined. If the signals are several avalanche received, can the superimpose transmitter signals of the transmitters each other and also obliterate one another. There two stations always slightly different from each repetition and / or duty cycles have, however, is essentially a mapping of the respective received signal possible to the one or the other transmitter. In the superposition of signals from several Transmitter is the sum of several periodically switched on and off Signals. Therefore, to the periodic components is the autocorrelation function, This sum signal to detect. For example, from the measured reception field strengths formed by threshold decision an on / off function are, the autocorrelation function of spectral lines at the frequencies contains. Thus, separation of the signals of multiple channels is possible. By averaging the auto-correlation function over several periods of observation can dominant periodic components relatively independent of the particular alignment of the transmitter are intended for receiver very reliable.

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

In further embodiments of the method the transmitter signals a transmitter with respect to transmitter signals of another station by a transmitter idenTificaTion individualized and there are processing signals which transmitter search angle a Assign this sender identification. This can group radio ions be realized in which, for 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 are represented by the following Description of an embodiment of the invention with reference to the accompanying Figures, of which:<dl tsize="11"><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 FIG. 1.</dd></dl>

In the figures for identical and functionally identical elements have the same reference numerals used.

FIG. 1 shows an embodiment of an inventively embodied search device 1 for use as avalanche victims search equipment (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 to issue a synthetically generated search tone to the user as Acoustic feedback and an LED 15, as is known for conventional devices. The speaker 14 and the red LED 15 permit conventional search without using the graphical display on the display 10th

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

The device 1 is designed as a combined search and transmission unit. The housing has the The form of a foldable mobile phone. The hinge is shown in FIG. 1 by a dashed Line 21 indicated. the device 1 is in search mode, by closing the Device automatically returns to the transmit mode. This is on Advantageously, a failback realized as, for example. in the event of Avalanche, is required by the standards.

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

A search process works from so that the searcher device 1 after switching departures from transmission to search operation several times to about 180 degrees swings back and forth. The achievable DF or search accuracy is initially about ± 10 degrees. When swiveling all transmitting or transmitter signals of the transmitters are detected by buried that in itself Range are. The range of the device is about 80 m. The transmitters can it be conventional transceivers, or identical to the device 1 Devices. A manual bearing, ie holding the device 1 in the direction of the strongest Signal, is not required.

The channels reported 22 to direction and distance on the display 10 displayed with the scale representation of the distance of the transmitter 22 from Seekers (the center of the coordinate field 16, ie, the reticle 23) Details on distance 24 is specified in meters.

The seeker can now by request of the victim, who discovered the first should be, and press the 12 "FINDING" key focus on this and the other channels 22 Hide. During the search, are distances 24 and position information 22 is constantly adapted to the current position of the seeker.

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

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

Is a Spilled found and rescued, the searcher removes the bearing and dedicated be the next victim.

The search device 1 is equipped with a motion sensor (not shown). This detecting whether the device 1 is moved. If the device is in any mode, is not the transmission mode, and the device over a period of 90 seconds not moving, then automatically switched to the transmit mode. This makes the also triggered aforementioned failback sure if the seeker due to an avalanche or the like surprising event no opportunity more has to collapse the search device.

The detector 1 has in the exemplary embodiment outlined here in addition to the Search on other functions that about with the key 13-to-reach are the main menu selected. This includes an electronic compass, a temperature display and tilt measurement for assessing the danger of avalanches, an indication of the Battery status and time remaining display for transmitting and search operation. At low Battery level is independent of the mode a warning.

Although the standard allows for security principle no additional functions (Compass, temperature display, tilt measurement). However, the required Search device according to the invention eg. The inclinometers to its operability. Then only, care must be taken to ensure that the display of additional Data obtained not the power consumption is increased so that the safety of is use is no longer guaranteed. Therefore, a safety circuit is in detector 1 provided (not shown), which switches off the display of the additional functions when the Battery capacity below 50% of the maximum value falls. Thus, the requirements of meets standard on the safety of the appliance.

In any other detection equipment according to the invention are only a few or none of these Additional functions before; thus also a safety circuit of the above described type accounts.

Furthermore, from the main menu of the search device 1 brief instructions for the device and configuration screens and Konfigurationseinstellmöglichkeiten for language and Display lighting achievable.

The integrated sensors, which are described in detail below, can Unit 1 to determine at any time, in which direction the seeker it just keeps. Thus, the position of the located transmitters of burials at any time correctly relative to own point of view are represented.

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

The technical realization of the detector 1 is performed in principle so that the received digitized 457- kHz signals and processed by a powerful microprocessor will. Algorithms of digital signal processing allow search tones, ie even more transmitter signals from the noise filter out, if they are already below the threshold sense of human hearing are. This allows for 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 about the entire search phase, the positions are continuously recalculated, improves Accuracy of the estimated position of the buried 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 search antenna and mixer for the search tone are a Sensor 30 for the earth's magnetic field, which a sensor signal for each degree of rotational freedom (X, Y, vertical) to write, as well as tilt sensors 32 provided for the two tilting axes. Additionally a further sensor 34 is for any of the above additional functions of the Device, the temperature measurement, located.

The microprocessor-controlled sample manager 36 performs the current sample the right target to and selects the channel for the next sample from. The time response is designed so that the maximum possible sampling clock for substantially the Sampling the received, ie transmitter signals is available. For the scanning of the Sensor data, the receiving signal as hidden each time slot and 32 instead of which one of the sensor channels for temperature, magnetic field and inclination is read.

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

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

to even locate buried in far away as possible. This matches with 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 - Optimally with a "matched filter" possible, which basically a cross-correlation between this and the received signal is carried out.

The matched filter has exactly the mirrored as impulse response along the time axis 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 occurs because therefore, that the pattern function in all possible phase positions with the sequence of Received, ie transmitter signals to be compared.

From the transmitter signal sequence is known that it is a cosine signal sequence is a constant frequency. Each arbitrarily scaled and phase shifted sinusoid can be decomposed into a cosine and a sine component. The performance of this signal is the sum of the powers of sine and Kosinusanteil. It is therefore sufficient, the transmitter-signal sequence with a cosine and a sine to multiply filter-signal sequence, the sequence of the transmitter signals so in a sine and disassemble a cosine component. The argument (angle) and through sine Cosine component formed complex number describing the phase position of the Received, ie transmitter signal sequence in relation to the cosine pattern function while the magnitude of the complex number is a measure of the reception field strength.

System In theory, the work in this manner, sin / cos correlator 40 a Demodulation of the search tone to baseband (multiplication by sin or cos) and subsequent low-pass filtering to suppress the image frequencies at the twice the signal frequency. is a major advantage of the sin / cos correlator 40 so that it can be constructed easily and conserve resources. Opposite to a matched filter detection performance worse by 3 dB. In RSS module 42 are from the output values ​​a (estimated amplitude value of the sine component) and b (amplitude estimate of the cosine) of the correlator 40 by quadratic averaging RSS ( "Received Signal Strength") - won values. The AKF-module 44 then computes the autocorrelation function (AKF) of the RSS values. The Edition of the ACF module 44 serves as a basis for separation of the signal components with several 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 can overlap each other and also obliterate one another. Because no two devices always slightly different from each repetition and / or duty cycles have, However, in principle, an assignment of the respective received signal to the one or the other transmitter.

In the superposition of signals of several transmitters is the sum more periodically and switched signals. Basically therefore suitable one 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 Orientation of the receiving antenna on the transmitter, the on / off times only may be insufficiently precisely determined. Through these inaccuracies are the Spectral lines of the autocorrelation function smeared, that is out of focus, and quickly unusable.

As well as in the ideal on-off function are the information about the Periodicity of course also present in the analog field strength function. This is a Amount of the output of the sin / cos correlator 40, that is, as the output of the RSS module 42 recovered. By averaging the auto-correlation function over several periods of observation can, dominant periodic components relatively independent of the respective Alignment of the transmitter to the receiver are determined very reliable.

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

The assignment of individual signal segments at different stations is determined by the heuristic segmentation segmentation module 46 made. These are the Substantially determined by threshold value signal that elements for Maximum of the AKF contribute. The signal elements thus determined are necessary, by Analysis of cracks in the correlation values ​​again separated and different assigned transmitters. A signal element may be, for example, starting from the left and right border in two separate areas on the edges and a - for the position estimate unusable - the superimposition area are divided in the middle. In order to segment can jumps and discontinuities in the sine and cosine correlation values be used.

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

The ferrite receiving antenna used in the receiver unit 28 has a cosinusoidal Directivity. In a stationary transmitter changes the received Field strength consequently by the cosine of double angle search. If the device pivoted from seekers while looking back and forth, so the angle continuously changed, can the location estimation module 48 thus in a simple manner the field strength σ are formed as a function of the search angle φ. 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 of successive Recording intervals for the same stations are determined, can by a weighted Averaging be continuously improved.

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 having a received signal strength indicate at a search angle, generally present only in sections. From the available sections, however, can use the method of least squares the determining parameters of the entire waveform is estimated. It can be calculated in a simple manner angle and distance of the transmitter.

In fault-free case could from the field strength during the station received signal sequence calculates the total field strength profile as a result of estimated angle signals will. To calculate sufficed any two points of the transmitter-signal sequence. In the Practice, however, more or less noisy, the reception signal. The approximation to used two points can then randomly heavily corrupted by noise samples be, so that the parameters of the actual angle signal sequence severely flawed to be appreciated. In order to achieve trouble-robust estimation, should all available included points of the received field intensity profile or the transmitter-signal sequence 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 from the Transmitter signals and search angles detected angle signals is minimal.

When applying the method of least squares, by the estimate Attraction of new metrics are continually being improved. First, it follows characterized even at great distances from the victim and correspondingly weak Search or received signal quickly, a relatively accurate location estimate. On the other hand leaves by an appropriate weighting of elderly in relation to their current values the measured or calculated, search angle signals a jumping or excessive suppress instability of the detected transmitter search angle can be reliably.

Thus, with sufficient number of measurements a reliable determination of Position of the transmitter possible. This is especially true when the maximum itself can not be detected because just at the time points at which the seeker Device in the direction of the transmitter shows the latter is in the pulse pauses. The data the real received signal provide guidance for the necessary number of samples for a sufficiently accurate determination.

Also object of the location estimate is the solution to the problem, from the field strength differences two or more consecutive recording intervals which dissolve 180 degree ambiguity the angle estimation and the sender of the front (in Movement direction) or the rear (against the direction of movement) be assigned to half-plane.

This is the location of a buried subject, in particular the transmitter search angle, even complete and reliable predictable when its transmitter which at that time to the device 1 of the seeker in his direction shows, is just in the intermission. This is achieved with an inventive design detector which only one having only search antenna and therefore be correspondingly easier and cheaper can (of course, the use of multiple antennas in an inventive Detector also possible).

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

The presentation of the features of the invention described as an example here Search device is based on modules, which in Fig. 3 as separate units marked. These units may be in the search device in the form of software, Firmware and / or hardware are present. Preferably, the modules are in the form of Software on a microprocessor / DSP before. For a full-featured search gadget as the illustrated reference to the figures would be a processor with 30 MIPS processing power and 8 KB of memory suitable.

Numerous variations of the search device described as an example here are conceivable. Thus, an inventive device without ACF module or module for separating the Signal components of several channels to be formed. Such a device is in situations use, where only one transmitter must be located. An example of this is a group of skiers on a secured piste is in the finding of the group leader by the detectors of the group members is made possible using only the TV channels of the conductor is in the transmit mode.

Also, an inventive detector without module for carrying out the formed cross-correlation of a filter signal with weak search or received signals be. Then weak signals in noise are no longer detectable, the Sensitivity of the search device is correspondingly reduced. However, then the Resources of the device (available memory, processor processing capacity) for other functions available, eg., the ACF module be configured to a greater number of transmitters to separate. Also, a functional device poorer with the same battery capacity over a prolonged period of operation have, when about 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. Of the Position of the seeker and detected by the detector transmitter locations, ie the suspected Liege points of burials, the display of the GPS system are superimposed. Such a system allows the seeker the position of Liege point based on any existing distinctive terrain points intuitively, ie to detect rapidly, so it with the least possible delay the sun point may seek.

Alternatively or additionally, the search device can be combined with a voice control are, as is known for motor vehicles as in GPS systems. This gets the Seekers 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, as is known for mobile phones. This is advantageous to the camera recorded terrain view displayed on the display of the search device. The channels covered places the terrain view are superimposed. 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 would GPS system and camera to achieve a detailed outline and rich representation of the terrain cooperate.

Instead only avalanche transceiver search unit, an inventively constituted Detector also advantageously be used for other applications. An example is a group of skiers called, which are based on their group leader, for example. when visibility is poor or otherwise confusing situation. All participants have send / detectors. The unit of the conductor has a transmitter whose Transmitter signal is provided with an individual transmitter identification. Devices of searching Group participants are designed for the evaluation of the received transmitter identifier, so that the located stations of the conductor identified among the plurality of the located transmitters is. 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 are all transmitters of a group by Micflag customizable.

Although the transfer of station names on the standardized signal is at 457 kHz not provided. However, could besides the otherwise standard compliant transmitter in a transmitter, a second transmitter can be provided which with the signals Micflag radiates.

In addition, within the scope of the invention solely by the following claims is stated by many craftsmanship action further embodiments are conceivable.

LIST OF REFERENCE NUMBERS

<dl tsize="6" 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>