EP0484880A2 - Radio alarm system - Google Patents

Abstract

A radio alarm system is described which offers adequate protection against interference due to blocking of the radio paths and against external manipulation. For this purpose, it is proposed that each signalling unit of the alarm system transmits at least two radio signals for an alarm signal, using a different carrier frequency and being coded in identical or different fashion. The central unit accordingly receives with its receivers the at least two radio signals from each signalling unit and checks the affiliation of the signalling units transmitting the radio signals by checking the validity of the coding. It is proposed in addition that an evaluation unit be provided in the receiver unit of the central unit which identifies the field strength of each received radio signal, analyses the associated data telegrams for affiliation to the system of the signalling units transmitting them, if an invalid data telegram is detected, compares the value of the received field strength of the radio signal concerned with a predefinable minimum value and, if this minimum value is exceeded by a predefinable amount, where this amount must be exceeded for a specific time period, triggers a warning indicator. <IMAGE>

Description

The invention relates to a radio alarm system according to the preamble of claim 1.

In security technology, there are guidelines for the installation of security systems, here in particular alarm systems, for private buildings as well as for commercial buildings, which have been developed and published by the Association of Property Insurers (VdS). These guidelines are based on VDE regulation 0833 and have been supplemented or modified by the Commission for Preventive Crime (KVK) since 01/01/1990 and brought up to date. In addition to the specific device requirements such as temperature behavior, minimum operating time, MTBF values, immunity to interference from electromagnetic fields and functional safety, these guidelines contain basic regulations for project planning for a safety system. These regulations are divided into three classes, which proceed from different groups of perpetrators: Class A only includes private houses that contain valuables up to DM 200,000.00, class B private houses with valuables over DM 200,000.00 and medium-sized commercial objects such as supermarkets, schools, shops etc. Class C includes jewelry stores, banks, etc.

With class A one assumes occasional offenders, with class B from perpetrators who, with a certain planning, also scout out objects beforehand and ultimately with class C from perpetrators who, after weeks of observation, may come to grips with extensive measuring instruments and special tools.

• a) Die sogenannte "Umweltverträglichkeit" beinhaltet die Anforderung, die Falschalarmwahrscheinlichkeit einer Anlagenkomponente als auch der gesamten Sicherungsanlage so gering wie möglich zu halten. Dies wird erreicht durch strengste technische Prüfungen beim Verband der Sachversicherer und zwar für alle Klassen gleich. Hier werden keine Unterschiede zwischen den Klassen gemacht.
• b) Die Möglichkeit eines unbeabsichtigten Falschalarmes durch den Betreiber und Eigentümer der Anlage absolut zu verhindern. Dies wird erreicht durch die sogenannte Zwangsläufigkeit, d.h. der Betreiber hat keine Möglichkeit in das scharfgeschaltete Objekt hineinzukommen, da durch mechanische Sperrelemente automatisch der Zugang bei scharfgeschalteter Anlage nicht möglich ist. Diese Sperrung wird erst bei Unscharfschalten aufgehoben.

In order to do justice to the perpetrator risk, which increases from A to C, the requirements for the system components as well as for the overall project planning of a system from A to C are increasing. The guidelines now contain further, also basic, requirements:

• a) The so-called "environmental compatibility" includes the requirement to keep the false alarm probability of a system component as well as the entire security system as low as possible. This is achieved through the strictest technical tests at the association of property insurers, and this is the same for all classes. There are no differences between the classes here.
• b) To absolutely prevent the possibility of an unintentional false alarm by the operator and owner of the system. This is achieved through the so-called inevitability, ie the operator has no way of getting into the armed object, since access to the armed system is not automatically possible due to mechanical locking elements. This block is only released when the system is disarmed.

Of course, all these requirements are subject to permanent functional checks and the resulting necessary maintenance of the entire system including its components. This is not particularly difficult in the case of wired systems, since the power supply on the one hand and any other on the other via the wire connection Information can be forwarded without problems. The dual power supply of the mains and the battery ensures that the second voltage will continue to operate even in the event of a power failure or battery failure.

Now the mentioned guidelines have led to the fact that up to the current state of the art, only systems wired with copper wire are able to meet all of these requirements. Since security systems are almost always retrofitted, mainly in private homes, the effort for the necessary cable routing inevitably meets with resistance from the customer. This conflict was taken into account on the part of the Association of Property Insurers in consultation with the criminal police commission for preventive crime to the extent that the so-called outer skin surveillance to be aimed at, in which each window is monitored for opening and breakthrough by appropriate glass breakage detectors, is dispensed with in class A. can. The surveillance here only extends to the access doors and the main focus is on passive infrared motion detectors in the rooms. This "minimization" reduces the cable effort, especially in the area of the windows, but all other necessary line connections to the external signal transmitters, to the doors, to the arming unit and to the infrared motion detectors still remain. It is clear that the monitoring quality suffers from this "minimization", since the perpetrator is already in the house through an unmonitored window before there is the possibility of triggering an alarm with a motion detector. These Reduction is however accepted with reference to the perpetrator group. The customer himself is in conflict because on the one hand he strives for surveillance directly at the house wall boundary, but on the other hand he opposes the necessary cable laying.

The only remedy here is a system which, on the one hand, does not require any cable laying, and on the other hand still complies with the guidelines of the Association of Property Insurers at least in Group A. The customer takes into account all so-called radio alarm systems, which are available in large numbers on the market, but according to the current state of knowledge, none of the systems meets the security requirements according to the guidelines of the Association of Property Insurers.

In order to illustrate the problems inherent in the known radio alarm systems, a typical system configuration and its mode of operation are first described with reference to FIG.

The radio alarm center according to FIG. 1 consists of the control unit 20a, a voltage supply device 20b, a radio receiver 20c and a radio transmitter 20d. An infrared motion detector 21a is connected to a voltage supply device 21b and to a radio transmitter 21c. In the event of an alarm event, the motion detector 21a issues a control command to the radio transmitter 21c. The latter then sends a so-called data telegram to the radio receiver 20c. The wireless alarm center handles the further processing.

The same applies to an opening contact 22a, for example on a door, which with a Power supply device 22b and a radio transmitter 22c is connected. To lock the system, a bolt switch lock 23a is used, which is connected to a mechanical locking element 23e, a radio transmitter 23c, control electronics 23d and a voltage supply device 23b. In the case of arming, a radio pulse is emitted to the radio receiver 20c of the alarm center via the radio transmitter 23c, whereupon the system is activated.

Furthermore, a telephone dialing device 24a is provided, which is connected to a radio receiver 24c, a voltage supply device 24b (for example a power supply unit with a battery emergency power supply) and a radio transmitter 24d. In the event of an alarm, the control center controls the radio transmitter 20d, which emits a radio signal to the radio receiver 24c. This radio receiver 24c controls the telephone dialer 24a via an output. The same applies to the radio transmitter 24d: this transmits a sabotage message to the radio receiver 20c of the alarm center.

Finally, an external siren 25a is provided, which is connected to control electronics 25d, a voltage supply device 25b, a radio receiver 25c and a radio transmitter 25e. In the event of an alarm, the external siren 25a receives a signal via the radio transmitter 20d and the receiver 25c. The receiver 25c controls the external siren 25a via the control electronics 25d. The radio transmitter 25e is used to transmit a sabotage message to the radio receiver 20c of the alarm center.

To the basic functional sequence of the To clarify radio transmission within the alarm system, reference is made to FIG. 2.

A detector 30 opens or closes its alarm contact and thus controls a switching logic 31. The same applies to a battery monitor 32 and a sabotage monitor 33. A fixed coding, which is set, for example, with dip switch switches or can also be hard-wired, is modulated together with the switching states in a modulation stage 34 and is transmitted via the transmitter 35 as already mentioned Data telegram sent. This data telegram is received by the receiver 36 and demodulated in the demodulation stage 41. In order to adapt the receiver 36 to the transmitter in terms of coding, it is also possible here to work either with dip switch switches or with hard wiring. If the data telegram is recognized as valid, the switching logic 42 controls e.g. outputs 38, 39 or 40. Usually 10 bits are used for transmitter identification (coding), so that 1024 codings are possible.

The descriptions given above correspond to the current state of the art (cf. US Pat. No. 4,511,887). There are also various special functions, such as a timed delivery of status based on the presence of each individual detector to the control center and, in the case of other systems, an evaluation of the incoming signal field strength (see US Pat. No. 4,603,325)

• 1) Es besteht die Möglichkeit der Blockung der Funkstrecken von außen durch starke Fremdsender gleicher Frequenz, die im Falle eines Alarmereignisses das Funksignal des betreffenden Alarmmelders überschatten, so daß die Alarmzentrale nicht auf das Alarmfunksignal reagiert.
• 2) Ferner ist die Möglichkeit der direkten Manipulation von außen mit einem anlagengleichen Funksender bei Durchprobieren aller möglichen Codiervarianten bei üblicherweise nur 1024 Kombinationsmöglichkeiten gegeben. Ist einmal die richtige Codierung gefunden, kann beliebig oft von außen eine Alarmfunktion provoziert werden, die sich zunächst als Fehlalarm erweist, aber eben auch einen gewissen Ermüdungseffekt bei dem Personal des angeschlossenen Wachunternehmens oder direkt beim Hauseigentümer mit sich bringt, so daß bei einem echten Alarmereignis, wie beispielsweise Einbruch, nicht adäquat reagiert wird.
• 3) Wird bei einr Funkalarmanlage, die von der Zentrale aus mit einer Signalfeldstärkeerkennung ausgestattet ist, ein Fremdsender erkannt, so muß die Zentrale diese Information in geeigneter Weise verarbeiten können. Die Möglichkeiten, die hier bestehen, sind folgende:
  • a) bei unscharf geschalteter Anlage kann ein interner Piepston generiert werden, so daß der bei unscharfer Anlage erwartungsgemäß sich vorort befindende Betreiber informiert wird und damit aber lediglich feststellt, daß die Anlage momentan nicht betriebsbereit ist.
  • b) bei scharf geschalteter Anlage (hier sei unterstellt, daß keine Person sich im Hause aufhält) muß die Zentrale diese Meldung weiterleiten über z.B. ein digitales Wählgerät zu einem Wachdienst. Der Wachdienst kann mit dieser Information nur sehr wenig anfangen, da er den Fremdträger ja nicht beseitigen kann. D.h., schließlich und endlich wird letzlich nur festgestellt, daß ein Fremdträger die momentane Funktion der Anlage behindert oder sogar außer Betrieb setzt. Aktive Gegenmaßnahmen können hier nicht getroffen werden.
• 4) Wie oben erwähnt, gibt es Alarmanlagen, die melderseits Statusmeldungen an die Zentrale abgeben. Hier wird vorausgesetzt, daß die Zentrale die Zeitintervalle der Statusabgaben kennt und eindeutig feststellen kann, ob eine Statusmeldung fehlt oder nicht. Fehlt eine Statusmeldung, z.B. beim Defekt einer Meldeeinheit, so muß die Zentrale ebenfalls darauf reagieren. Hier gibt es wieder die folgenden Möglichkeiten:
  • a) bei unscharfer Anlage kann ein Piepston oder optischer Anzeiger generiert werden.
  • b) bei scharf geschalteter Anlage muß eine Information, z.B. zu einem Wachunternehmen, weitergeleitet werden. Das Wachunternehmen kann auch mit dieser Information nicht viel anfangen. Hier müßte der Facherrichter, der Installateur der Anlage, informiert werden, um einen evtl. Fehler melderseits festzustellen und zu beheben. Bei scharf geschalteter Anlage kann aber der Errichter in das Haus nicht hinein, da üblicherweise die Errichter keine Schlüsselgewalt haben. Auch hier könnte aber der Grund für das Fehlen einer Statusmeldung das Anliegen eines Fremdträgers gleicher Frequenz (siehe Punkt 4 und Punkt 1) sein, so daß nicht unbedingt von einem Defekt eines Teils ausgegangen werden kann.
    Aus der US-PS 4,511,887 ist gleichfalls bekannt, daß zur Abfrage des Status der einzelnen Melder zusätzlich zu dem Sender in den Meldern ein Empfänger integriert wird, der Signale von der Zentrale als Anforderung erkennt, seinen Status über seinen Sender an die Zentrale abzugeben. Die Zentrale kann dann aus dem ankommenden Statussignal des Melders mit Hilfe einer in der Zentrale integrierten Signalfeldstärkeerkennung die Signalfeldstärke des Melders detektieren und anzeigen. Es ist in dieser Druckschrift allerdings nicht ausgeführt, ob die Zentrale nach Abfrage einer Statusmeldung und Nichterhalt einer Antwort beispielsweise eine Störungsmeldung generiert. Die Auswertung des Signalfeldstärkewertes ausschließlich aus den Melderdaten zeigt nicht auf, ob gleichzeitg ein Träger gleicher Frequenz aufliegt, der die Signalfeldstärke evtl. mindert.
• 5) Bei Funkalaramanlagen, die eine Batterieüberwachung melderseits integriert haben, wird diese Batterieüberwachung teilweise nur am Melder selbst angezeigt, teilweise ebenfalls per Funkstrecke an die Zentrale weitergeleitet. Auch hier besteht die Möglichkeit, gemäß Punkt 1, der Blockung dieses Informationssignals, wobei das Informationssignal, wenn nur kurzzeitig, also mit einem Funkimpuls abgesendet, ganz verloren gehen kann, wenn ein Fremdträger aufliegt. Andererseits - wenn das Informationssignal als Dauersignal gesendet wird - ist die Funktion des Melders nach einigen Stunden gänzlich außer Betrieb, da durch das Dauersenden des Signals die Batterie erschöpft ist.
• 6) Bei den Funkalarmanalgen, die mit Sender und Empfänger in den einzelnen Meldern arbeiten, ist es notwendig, eine ausreichend dimensionierte Spannungsversorgung für die Betriebsbereitschaft, zumindests des Empfängers und der Auswerteschaltung, bereitzustellen. Da der Empfänger zu viel Strom im Betriebszustand benötigt, ist bei diesen Anlagen ein Batteriebetrieb nicht möglich.

All these known radio alarm systems have the advantage that no complex wiring has to be carried out, so that the installation times are short. They are also at Moves completely reusable. However, they have the following serious disadvantages:

• 1) There is the possibility of blocking the radio links from outside by strong third-party transmitters of the same frequency, which in the event of an alarm event overshadow the radio signal of the alarm detector in question, so that the alarm center does not respond to the alarm radio signal.
• 2) Furthermore, there is the possibility of direct manipulation from the outside with a radio transmitter of the same system when trying out all possible coding variants with usually only 1024 possible combinations. Once the correct coding has been found, an alarm function can be provoked from outside as often as desired, which initially proves to be a false alarm, but also has a certain fatigue effect on the staff of the connected security company or directly on the house owner, so that in the event of a real alarm event , such as burglary, is not adequately reacted to.
• 3) If a third-party transmitter is recognized in a radio alarm system which is equipped with signal field strength detection from the control center, the control center must be able to process this information in a suitable manner. The options here are as follows:
  • a) when the system is disarmed, an internal beep can be generated, so that the operator, who is expected to be on site when the system is disarmed, is informed and thus merely determines that the system is currently not ready for operation.
  • b) if the system is armed (it is assumed that there is no one in the house), the control center must forward this message to, for example, a digital dialer to a security guard. The security guard can do very little with this information, since he cannot remove the third party. That is, finally and finally, it is ultimately only found that a third-party carrier impedes the current function of the system or even stops it. Active countermeasures cannot be taken here.
• 4) As mentioned above, there are alarm systems that send status reports to the control center. Here it is assumed that the control center knows the time intervals of the status deliveries and can clearly determine whether a status message is missing or not. If a status message is missing, for example when a reporting unit is defective, the control center must also react to it. Here are the following options:
  • a) A beep or visual indicator can be generated when the system is unset.
  • b) if the system is armed, information must be passed on, for example to a security company. The security company cannot do much with this information either. The specialist installer, the installer of the system, would have to be informed here in order to determine and rectify a possible error on the part of the report. If the system is armed, the installer can not into the house, as the installers usually have no key authority. Here too, however, the reason for the lack of a status message could be the presence of a third-party carrier of the same frequency (see points 4 and 1), so that a defect in a part cannot necessarily be assumed.
    From US Pat. No. 4,511,887 it is also known that in order to query the status of the individual detectors, a receiver is integrated in the detectors in addition to the transmitter, which detects signals from the control center as a request to transmit its status to the control center via its transmitter. The control center can then detect and display the signal field strength of the detector from the incoming status signal of the detector with the aid of signal field strength detection integrated in the control center. However, it is not stated in this document whether the control center generates, for example, a fault message after a status message has been queried and a response has not been received. The evaluation of the signal field strength value exclusively from the detector data does not show whether there is simultaneously a carrier of the same frequency, which may reduce the signal field strength.
• 5) In the case of radio alarm systems that have battery monitoring integrated on the detector side, this battery monitoring is sometimes only displayed on the detector itself, and in some cases also forwarded to the control center via radio link. Here, too, there is the possibility, according to item 1, of blocking this information signal, the information signal being lost entirely if only transmitted briefly, ie with a radio pulse can go if there is an external carrier. On the other hand - if the information signal is sent as a continuous signal - the function of the detector is completely out of operation after a few hours, since the battery is exhausted by the continuous transmission of the signal.
• 6) In the case of radio alarm systems that work with the transmitter and receiver in the individual detectors, it is necessary to provide a sufficiently dimensioned power supply for operational readiness, at least for the receiver and the evaluation circuit. Since the receiver requires too much power in the operating state, battery operation is not possible with these systems.

Known radio alarm systems do not meet the VdS guidelines, in particular because of the possibility of manipulation from outside and the possibility of blocking the radio link by third-party transmitters.

The invention has for its object to provide a radio alarm system which does not have the disadvantages of known systems described. In the system according to the invention, manipulation from the outside, in particular with identical transmitters, and intentional or unwanted blocking of a transmission from a radio transmitter to the alarm center or from the alarm center to an alarm device should not be possible, or should be possible only under very difficult circumstances. Furthermore, all components (with the exception of the alarm center), in particular the signaling units, should be operated with a commercially available battery with transmitter and receiver.

The object is achieved by the radio alarm system according to claim 1. Further advantageous developments are specified in the subclaims.

According to the invention, it is accordingly provided that the reporting units each emit at least two radio signals for the same message, which have a different carrier frequency and are encoded in data telegrams of fixed, predetermined coding, that a device is provided in the receiver unit of the central unit which detects the field strength of each received radio signal, the data telegrams are analyzed for the affiliation of the reporting units that they deliver to the system, in the event that an invalid data telegram is found, compares the value of the received field strength of the radio signal in question with a predetermined minimum value and, if this value is exceeded, by a predeterminable amount and after a certain period of time has elapsed, the is preferably about 10 seconds, triggers a warning display. The background to this security measure is that the signal signals of the respective transmitter modules with the associated field strengths can be stored in the central unit, so that the at least valid field strengths that arrive are known. The device in the central unit can therefore decide whether the incoming field strength with an invalid data telegram is strong enough to block a possibly valid message from the transmitter modules. If an invalid data telegram is received, the device decides whether the associated field strength exceeds the minimum value of a valid radio signal. If so, a warning is triggered.

According to a further embodiment it is provided that the said device triggers each radio signal by the predeterminable amount of alarm upon detection of the invalidity of all received data telegrams and when the minimum values of the field strengths which are stored as described are exceeded. In this case, the entire radio system is inoperable.

A blocking of a transmission path from a detector with a transmitter unit, which emits at least two radio signals, to the central unit is thus avoided by using several transmitter-receiver pairs with different frequencies, so that even if a transmitter-receiver is interrupted or disturbed, Route the other transmitter-receiver routes remain in operation. The likelihood of wanted or unwanted blocking of a transmission link decreases drastically with increasing number of transmitters and receiver modules used in the reporting unit or in the central unit.

A deliberate manipulation from the outside is prevented by the fact that the reporting units each have at least two transmitters and two receivers and that after a reporting unit has sent its signals to the control center via the transmitters, the request comes from the control center to the reporting unit, this message to confirm again. Security can be further increased here by coding the at least two radio transmitters that are assigned to each detector unit differently. This increases security with 10-bit coding of each transmitter by the exponent 10 for each additional transmitter.

Battery operation of the signaling units is achieved in that the entire circuits in the signaling unit as well as the receivers and the transmitters are only activated when an event occurs. When a signaling event occurs, the voltage supply for the circuit and the transmitters is switched on via a signaling relay located at the detector output. The circuit associated with the receivers is switched on by means of at least one HF detector when an incoming input signal is received. The at least one RF detector monitors the signal energy that is applied to the antenna. If the receivers and the downstream circuitry determine that this is a valid signal (as a rule, valid input signals are a request from the control center to carry out a status report or signal repetition), the transmitters are activated. However, if it is determined that an invalid signal is present, the subsequent circuit switches itself and the receivers immediately off from the voltage supply. Since a permanent external carrier permanently generates a signal energy on the antenna, the HF detector (s) would also put the circuit into operation permanently and thus cause the voltage source to soon be exhausted. In order to avoid this, each of the HF detectors is advantageously preceded by a dynamization element, which only puts the circuit into operation or switches on the voltage supply in the case of newly arriving input signals.

In addition, it is provided in a further embodiment to provide the signaling units with double battery monitoring. This means that two thresholds of the battery voltage are monitored, a signal being triggered when the first threshold is undershot if the battery continues to function for about 2-3 weeks. If the supply voltage falls below the second, lower threshold, a radio signal is emitted, on the basis of which the control center recognizes that the battery is empty and generates an alarm signal or a signal preventing the system from being armed. For this purpose, the alarm center can be constructed in such a way that a signal is set when the battery arrives for the first time, for example a light-emitting diode at the center or a display, so that the operator is informed in good time of the battery that will soon be exhausted. The background to this measure is that in the event of a fault message - and this is the case in known systems with a single battery message - the operator may no longer be able to arm the system. In addition, it cannot be assumed that the operator has the right spare battery in stock. The measure according to the invention of monitoring two threshold values ensures that there is a sufficient period of time after receipt of the notification of the battery falling below the first threshold, since the operator is able to sharply close the system until the message falls below the second threshold switch.

Figur 3:

Das Prinzip des melderseitigen Senderaufbaus und das Prinzip des Empfängeraufbaus in der Zentraleinheit der Alarmanlage,

Figur 4:

weitere Einzelheiten einer Sender- und einer Empfängereinheit, und

Figur 5:

ein Prinzipschaltbild einer Meldereinheit mit Sender- und Empfängeraufbau sowie mit einem, dem Empfänger vorgeschalteten HF-Detektor.

The radio system according to the invention is explained in more detail using an exemplary embodiment. Here shows:

Figure 3:

The principle of detector construction on the detector side and the principle of Receiver structure in the central unit of the alarm system,

Figure 4:

further details of a transmitter and a receiver unit, and

Figure 5:

a schematic diagram of a detector unit with transmitter and receiver structure and with an RF detector upstream of the receiver.

The circuits shown can be implemented in a radio alarm system with the units, as has already been explained with reference to FIG. 1.

FIG. 3 shows an example of the structure of a transmitter module of a detector 1, for example an infrared motion detector. Control electronics 2 are arranged within a housing 27 which is advantageously made of metal and which is controlled by signals from detector 1 via lines 3. This information is forwarded by the control electronics 2 via a line 4 to a modulation stage 5, the coding of a hard-wired coding stage 6 being adopted by the modulation stage 5 and processed into a common data telegram and finally being forwarded to the transmitter unit 7. A voltage supply 8 supplies all components of the module, the voltage of the voltage supply 8 being constantly checked by a voltage monitoring unit 9. The sending unit sends all information to the receiver level in the alarm center. The receiver stage consists of a receiver unit 10 which sends the incoming radio signals to a Demodulation stage 11 passes on, from where the data telegrams in the evaluation stage 12 for data telegrams are checked for validity - or invalid - on the basis of the coding assigned to the respective detector 1 and in which the information content of the transmitted switching states is simultaneously forwarded to the interface 13. The switching states contain information regarding the current state of each detector. A central controller 14 takes the information present from the interface 13 and forwards it to a processing stage 15 or to the display 16. The receiver unit 10, the demodulation stage 11 and the evaluation stage 12 for the data telegrams are preferably arranged in a metallic housing 17 in order to avoid electromagnetic interference.

FIG. 4 shows further details of the transmitting and receiving modules.

Each transmission unit 22 consists of several transmitters a to n, which emit signals with different carrier frequencies. The transmitted signals are encoded. The transmitters a to n receive the codes from a likewise n-stage modulation stage which is connected upstream of the transmitter unit 22. The modulation stage 21 imprints codings on the signals, which it receives from the n-stage coding stage 20 connected upstream of it. Switching states are also added to the coding via a line 28. The transmitter unit 22 thus sends n radio signals, each of which has a different frequency and is coded differently. According to a simplified embodiment, it is possible to give the same coding to all n radio signals.

An n-stage receiver stage 23 is provided on the receiver side, which receives the n radio signals of the transmitter unit 22. Each receiver a to n is assigned to the modulator a to n in a demodulation stage 24. The demodulated signals are fed via a line 29 in the present exemplary embodiment to the evaluation stage 12 for data telegrams as shown in FIG. 3.

In addition to supplying the received radio signals a to n to the demodulation stage 24, the received signals are fed to an analog / digital converter 25. This transmits the converted signals to an evaluation unit 26. This structure enables the received field strength of the individual radio signals a to n to be monitored. The evaluation unit 26 checks whether the data telegrams associated with the individual radio signals a to n are valid or invalid, that is to say that is, whether they come from a unit belonging to the radio alarm system or not. If the check reveals that a data telegram is invalid, the field strength size is used to determine whether there is a radio interference. For this purpose, the messages from the respective transmitters a to n with the associated field strengths are stored in the evaluation unit 26, so that the at least valid field strengths arriving are known. Accordingly, it can be decided whether the received field strength of a received radio signal with an invalid data telegram is strong enough to block a valid message from the transmitter. If such a field strength exceeds the stored value for field strengths of signals with a valid data telegram, this can be done in the display device are displayed. The evaluation unit 26 is also designed so that it triggers an alarm when it is determined that all incoming data telegrams are invalid and all field strengths exceed the said minimum value for a predetermined period of time, since in this case the alarm system is inoperative.

Figure 5 shows an example of the structure of a detector unit 1, e.g. of a motion detector. The entire detector unit is advantageously located in a metal housing 56, although the detector 73 can also be located outside of this housing. In the basic state, the receiver unit 63, which consists of at least two receivers for different carrier frequencies, as well as the processor or the circuit electronics 61 and the transmitter unit 62, which consists of at least two transmitters with different carrier frequencies, are de-energized because the switching elements 53 and 54 supply the voltage interrupted by open switch. Furthermore, the transmit / receive switch 65 is in the "receive" position.

If an event is now registered by the detector 73 or by the battery monitoring 64, the signal outputs C ', D' or E 'in the event of a reporting event or signal outputs A' or B 'in the event of a battery monitoring event become the processor 61 via lines 69 fed. At the same time, the processor 61 is connected to the supply voltage of the battery 50 via the signal outputs A to E. This causes the processor 61 to close the switching element 54 via the line 60 and thus also to supply the transmission unit 62 with voltage. The information is prepared in accordance with radio technology to the Transmitter unit 62 passed on, whereby before the signal is passed on to the transmitters the processor 61 switches the transmit and receive switch 65 to "transmit" via a line 72, so that the transmit unit then leads via line 70 to the transceiver switch 65 and further to the antenna 55 can send their signals. Since the signal outputs from the detector or from the battery monitoring switch on the necessary voltage supply only very briefly, the processor has its own coupling 71 to the battery 50, which it maintains until the transmission unit has sent the data telegrams via the antenna 55. Only then is the power supply for the transmitter unit switched off via the line 60 and the switching element 54, then the transmitter and receiver switch 65 is switched back to "reception" via line 72. The processor 61 now waits for a certain period of time for the request from the central unit to repeat and thus to confirm the previously emitted signal. If no request signal is received, the processor 61 causes the transmission unit 62 to transmit this signal until the request from the central unit is received. After receiving this signal, processor 61 switches itself off via voltage coupling 71. If a radio signal is received by the antenna, either transmitted by the alarm center or if there is a third-party carrier of the same frequency, a pulse is produced by the transmitting and receiving switch 65 from the applied signal in the dynamization element 75, which is generated by the RF detector 51 is evaluated in such a way that it closes the switching element 53 via line 80 and thus switches on the voltage supply for the receiver unit 63 and the processor 61. After switching on the power supply 50, the Receiver unit 63 feed the incoming data signal to the processor via line 82. The processor 61 then decides whether it is a valid data telegram or not. In the former case, the transmission unit 62 is activated via line 60, the transmission and reception switch 65 previously switched over to transmission mode via line 72 and then the transmission unit is instructed to send data telegrams prepared by the processor to the control center. In the second case, if it is an invalid data telegram, the processor is programmed so that it opens the switching element 53 or its switch via line 83 and thus switches off the power supply or the voltage supply for the receiver unit 63 and the processor 61. If the detector 73 emits an alarm signal to the processor via the information line 69, and if this information is forwarded via the processor 61 and the transmission unit 62 to the alarm center, and if the alarm center is in an armed state, the alarm center will prompt the notification unit 1 to to confirm the information given again. The processor 61 is now requested via the receiving side to activate the transmitting unit 62 again for the same information delivery. Since with the renewed request on the part of the control center, this also sent the information about its armed state, the processor now knows that it must control the memory display 78 of the detector 73 via the line 77. At the same time, the signal is sent via the transmitting unit 62 to the receiving center, which then triggers an alarm.

Claims (5)

Radio alarm system, consisting of a central unit with a receiver unit for receiving radio signals from signaling units in the form of data telegrams, each representing an event, the receiver unit being matched to the radio signals in such a way that it can only process data telegrams from signaling units belonging to the system trigger an alarm or function

characterized,

that the signaling units (1) each emit at least two radio signals for the same message, which have a different carrier frequency and are encoded in data telegrams of fixed, predetermined coding, that an evaluation unit (26) is provided in the receiver unit of the central unit, which detects the field strength of each received radio signal , the associated data telegrams are analyzed for the affiliation of the reporting units they issue to the system, in the event that an invalid data telegram is found, compares the value of the received field strength of the radio signal in question with a predetermined minimum value and, if this minimum value is exceeded, by a predefinable value Amount, which amount must be exceeded for a certain period of time, triggers a warning display. Radio alarm system according to Claim 1, characterized in that the evaluation unit (26) triggers the alarm by the predeterminable amount when all the data telegrams received are found to be invalid and the field strengths of each radio signal are exceeded. Radio alarm system according to claim 1 or 2, characterized in that the central unit additionally has at least two transmitters for transmitting signals for status queries of each reporting unit (1), that each reporting unit (1) each has at least two transmitters forming a transmitting unit (62) and at least two one Receiver which forms the receiver unit (63) has a mains-independent voltage source (50) which can be placed on its active components on request by switching elements (53, 54), the switching on of the voltage source (50) and thus the activation of the transmitter and receiver units (62, 63) by at least one HF detector (51) connected downstream of the antenna (55), such that the transmission energy emitted by the transmitters of the central unit and received by the receiver unit (63) of the signaling unit (1) changes the switching state of the HF detector , which in turn controls the switching elements (53, 54). Radio alarm system according to Claim 3, characterized in that a dynamization element (75) is connected between the antenna (55) of the signaling unit (1) and the HF detector (51). Radio alarm system according to one of Claims 1 to 4, characterized by two threshold value comparators which compare the supply voltage of the signaling units with two different threshold values, the signaling unit entering a first radio signal when the voltage falls below the one, higher threshold value and falling below the second, lower threshold value second, triggering alarm or arming of the system preventing radio signal to the central unit.

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