System and signalling apparatus for broadcasting an emergency warning

The present invention relates to a system for broadcasting an emergency alert over an area at a location, the system comprising at the location a source of audible or visual warning signal detectable by at least one of the human senses and at the location Transmitter for emitting an electromagnetic warning signal within a tunable bandwidth of a standard radio receiver for receiving commercial broadcasts, wherein at least a portion of the electromagnetic warning signal is encoded in an RDS compatible format.

Various products have been developed to alert the general public to the occurrence of unusual situations which sometimes require action to protect life and property. These products include applications for large areas and for local areas. For local area products, the alarm task is usually taken over by a visible and / or audible signal, such as flashing or rotating lights and sirens. Local area products are widely used in emergency vehicles. Such systems are designed to warn the public in the vicinity of the vehicles. Large area products are discussed in the United States Emergency Broadcast System, which uses large area RF transmitters to transmit emergency signals over a wide geographic area.

In general, the alarm products emit light, audio or radio frequency (RF) signals. Light and audio are attenuated relatively rapidly relative to RF signals as they propagate. This feature makes alarm products that emit light and / or audio signals particularly suitable for warning only in a range of a few hundred meters (yards) about the location from which the broadcast originates - ie in a local area. In addition, light and audio signals are directly perceptible by the human senses. On the other hand, RF signals are less attenuated by the atmosphere than light and audio signals, and therefore, depending on the signal power at the location of the broadcast, they can be used to provide warning signals over a wide range of several kilometers (miles) or more - ie in a large area. In addition, RF signals penetrate most building materials without significant attenuation, making them particularly suitable for transmitting warning signals to a building or other environment which isolates the occupants from environmental conditions.

Although the range of RF signals is much more dynamic than light and audio signals, RF signals have the distinct disadvantage of requiring the receiver of the signals to have a device to convert the RF signals into signals. which can capture one or more of the five senses of the recipient. In the past, typical large area RF-based warning systems have used conventional AM / FM receivers as the device for converting the RF signal. In these systems, a commercial broadcaster agrees to use its transmitter as part of the community warning system.

The transmitters used by these commercial broadcasters are typically high performance immovable devices. In the United States, a national emergency network of this kind is the Emergency Broadcast System. The network consists of a number of large-scale broadcasting stations intended to cover the United States with an emergency RF signal that can be received by conventional receivers. These emergency broadcasts using commercial broadcasting systems lack flexibility and are intended to fully cover large geographic areas.

Traditional warning products that emit audible and / or visible warning signals are well-suited for use in local areas. However, they are of decreasing efficiency when those who are to receive their signals are in an isolated environment or an environment that is littered with other audible or visible "signals" - such as urban areas. For example, flashing lights are only noticeable within a direct line of sight, and they can not be seen around the corners of buildings, which is a problem particularly in urban areas. Similarly, sirens may not be heard by persons with reduced or absent hearing or in noisy vehicles, urban streets or well-insulated buildings. Other factors that reduce the effectiveness of local warning systems include the use of audio systems in a vehicle; heavy traffic; Weather conditions that make it necessary to close the windows; and the sound of forced ventilation systems. In addition, vehicles and buildings have recently been better insulated, further increasing the masking of audible or visible warning signals. These signal masking problems increase the likelihood that an audible or visual warning device will not be noticed in a vehicle or building.

Even though local area warning devices are used by almost all emergency vehicles, such vehicles themselves often suffer from a diminished awareness of other emergency situations. For example, a fire truck moving in an emergency mode typically generates audible and visual warning signals to warn the motorized public and pedestrians that the truck is operating outside normal traffic flow conditions (e.g. high speed and opposite to the roadway and to signal controls). When two or more vehicles respond to an emergency from different starting points, they typically approach the emergency along various routes, thus becoming at risk for one another. In addition to the increased risk of movement in an unusual manner, the emergency warning siren or warning lights of a first vehicle tend to mask the ability to sense warning lights or sirens from other emergency vehicles.

Various proposals have been made to overcome these problems of traditional local area warning devices. Some proposals have used equipment designed to transmit local area alert signals over RF links. For example, known systems have used a special transmitter located in an emergency vehicle and also special receivers in the vehicles or locations to be warned. These systems require the installation and maintenance of RF receivers in addition to the conventional RF receivers for commercial bandwidths that are normally in the vehicle or in the house, and therefore these systems have not been accepted by the market. The lack of widespread use of such products is partly due to the perceived poor cost-benefit ratio for specific receivers that occupy significant space (especially in a vehicle) and are rarely used. Further, when in use, the user may consider the conventional audible and visual warnings to be single and conclude that the particular recipient is merely an additional and unnecessary improvement.

Another problem with known local area warning systems using RF links is the practical difficulties associated with installing additional emergency radio equipment in a vehicle. Mounting problems are increasingly associated with the downsizing of vehicle passenger compartments, along with limitations on the mounting locations of such additional equipment. These limitations are related to the failure of inflation of the airbag and the like.

A system for broadcasting an emergency warning, as described above, is disclosed in DE 39 15 099 A1. The prior art movable alert system of this prior art includes a receiver responsive to radio frequency or optical signals transmitted by a mobile transmitter and also capable of processing RDS alert signals.

It is the primary object of the present invention to provide the increased alerting capability of prior art local area systems using RF links without the need for special receivers.

The invention is defined by the appended claims.

According to the invention, this object is achieved in an above-mentioned system for broadcasting an emergency warning by means of a power amplifier in the receiver whose power design provides for an effective range of the electromagnetic warning signal which complements and substantially coincides with an effective range of the audible or visible signal . and solved by means for detecting the electromagnetic warning signal within its effective range and in response thereto for tuning the receiver to the carrier frequency of the electromagnetic warning signal.

In a local area warning system, the invention uses conventional electronic devices, which are available in virtually all homes and vehicles, to receive warning signals that complement the local or collective audible and visual warning signals. It is a related advantage of the invention that it complements an audible outdoor community warning signal with an additional signal that can enter the relatively isolated environment of a typical modern home or vehicle.

According to another advantage of the invention, there is provided an improved warning system which warns a person of the presence of an emergency vehicle in the surrounding area near the vehicle, or other unusual situations, even when the person is in an environment isolated to some degree or masked to the audible and visible signals emitted by the vehicle.

According to one aspect of the invention, a transmitter is provided to emanate a local warning signal from a mobile location such as an emergency vehicle, or from a fixed location such as a siren mounted on a tower, the warning signal being at a carrier frequency F & sub0; within a tunable bandwidth of a standard radio receiver for receiving commercial broadcasts. It includes control signals in a sideband which are encoded in a Radio Data System (RDS) compliant format. Because the warning signal is intended to provide a local warning supplementing the conventional visual and audible warning signals, the transmitter's power amplifier has a power design that produces a transmission range whose effective range is approximately equal to the range of the visible and audible Signals under ideal conditions.

When used in an emergency vehicle, the transmitter is preferably adapted to a transceiver which establishes a communication link between emergency vehicles within a range which is approximately the same as the range covered by the signals of the transmitter. The transceiver operates within a bandwidth that is different from the bandwidth of the transmitter. For example, the transmitter preferably broadcasts within the tunable range of a standard FM receiver, while the transceiver may broadcast within a bandwidth allocated to the police and other community services.

When used in a fixed location, the transmitter is typically used alone. Turning on the transmitter, however, is usually accomplished in conjunction with a visual or audible signal of conventional type. For example, most communities have a network of sirens strategically located across the population to ensure that the warning signal shared by the sirens reaches everyone. With each siren, or with a siren located approximately in the middle of a group of sirens that are controlled together, a transmitter according to the invention is activated with the activation of the siren or the group of sirens.

Preferably, in any of the foregoing embodiments, the warning signal is selected to have a carrier frequency F & sub0; at the upper or lower end of the tunable range of a commercial FM bandwidth - ie 87.5 MHz to 108.0 MHz in the United States. An audible warning signal is output at the carrier frequency F & sub0; transmit (ie siren, tone or speech) and control signals are transmitted on a sideband (SB) frequency of the carrier frequency. The control signals are encoded for decoding by the receiver in RDS format. The receipt of the RDS coded control signals by a receiver causes the receiver to respond to commands decoded from the control signals, which typically results in retuning of the receiver to the carrier frequency F0. for the purpose of demodulating the warning signal and delivering the warning signal to the speaker connected to the receiver.

To ensure that the receiver operates in a normal mode while retaining the ability to detect control data on the SB frequency, the receiver comprises two input circuits. An input circuit is controlled by the user to select a desired commercial FM broadcast transmitter in the conventional manner of operation of an FM receiver. A second input circuit either scans the tunable FM bandwidth and looks for control signals on any SB frequency, or is on the selected emergency carrier F & sub0; tunes its SB frequency continuously to control signals. In each of these architectures of the input circuit, the receipt of a control signal by the second input circuit causes the receiver to switch its amplifier circuit to the second input circuit, and that of the frequency F & sub0; to broadcast the transmitted warning signal. Therefore, the receiver may, for example, play music or the like in a conventional manner, which could lead to isolation of the environment or to an increase in such isolation. Upon receipt of control signals from the emergency vehicle, the receiver changes its conventional mode of operation to an emergency mode, providing an audible and / or visual indication warning the user of the receiver of the presence of an emergency situation when the user is within an area within the area Near the transmitter is located.

When used in an emergency vehicle, both the transmitter and the transceiver may include automatic gain control (AGC) responsive to the speed of the emergency vehicle to control the range of the transmitted signals in proportion to the speed of the vehicle. Further, further improvement involves shaping the radiation characteristic of the emergency signals emitted by the transmitter and the transceiver to direct the signals in a manner that best suits the situation. For example, when the vehicle is parked, the radiation pattern may be shaped to form two complementary lobes, one facing forward from the vehicle and the other toward the rear. Such a characteristic would best warn approaching traffic without unnecessarily alerting the surrounding neighborhood or distant intersections.

Finally, the on-board transceiver may include information describing the condition of the vehicle for use by a receiving emergency vehicle. For example, sensors on board the emergency vehicle may provide information about the speed, direction, and instantaneous position of the vehicle. This information may be decoded in the transceiver of the receiving emergency vehicle to provide a visual indication of the position, direction and speed of the transmitting vehicle. For example, the display may be a simple vector arrow whose position, orientation and length on the screen are determined by the position, direction and velocity data, respectively.

While the invention will now be described in some detail with reference to the preferred and alternative embodiments, it will be understood that it is not intended to limit the invention to such details.

FIG. 1 is a simplified block diagram of an emergency vehicle system (EVS) in accordance with an embodiment of the present invention in which RF communications links are established between two emergency vehicles and from the two emergency vehicles to a conventional FM receiver;

Fig. 2A is a schematic illustration of the tunable bandwidth of the conventional FM receiver of Fig. 1, including an area within the bandwidth approved for commercial broadcasts and an area for transmitting emergency signals according to the invention at each end of the bandwidth;

Fig. 2B is a schematic representation of two emission characteristics radiated by alternative antenna arrangements, the first arrangement (i) providing substantially omni-directional characteristics and the second arrangement (ii) providing elongated characteristics;

Figures 3A through 3E are pictorial representations illustrating various applications of the invention, wherein

3A is an illustration of an application of the invention wherein both the transceiver and transmitter of FIG. 1 are mounted in an emergency vehicle to broadcast information and warning signals to other emergency vehicles as well as to "civilian" vehicles.

FIG. 3B is an illustration of an application of the invention wherein only the transceiver of FIG. 1 is mounted in an emergency vehicle to broadcast information and warning signals to other similar transceivers typically mounted in other emergency vehicles;

FIG. 3C is an illustration of an application of the invention where only the transmitter of FIG. 1 is mounted in an emergency vehicle to broadcast information and warning signals to conventional FM receivers in "civilian" vehicles; FIG.

FIG. 3D is an illustration of the invention in which only the transmitter of FIG. 1 is associated with one of a plurality of exemplary stationary warning systems and configured to supplement the conventional visual and audible warnings used by the stationary system, and FIG

Fig. 3E is an illustration of an application of the invention to a school bus in which the transmitter of Fig. 1 is turned on by the pop-up of a STOP sign on the side of the bus;

4 is a schematic illustration of an RF system aboard one of the emergency vehicles of FIG. 1 depicting an exemplary control panel for the transceiver and transmitter of the system and also various sensor inputs whose data characterize a condition of the vehicle;

Fig. 5 is a more detailed schematic illustration of the RF system of Figs. 1 and 4 showing additional details of the transceiver, transmitter and controller of the RF system;

Fig. 6 is a diagram showing the preferred coding structure for the control data which is broadcast in a sideband of the carrier frequency F0 to which the transmitter of Fig. 1 is tuned;

Fig. 7 is a logic flow diagram for the operation of the transmitter and transceiver of the RF system in one of the emergency vehicles shown in Fig. 1;

Fig. 8 shows a block diagram of a receiver for receiving commercial AM and FM broadcasts, as well as the carrier frequency F 0 transmitted by the transmitter in Fig. 1 and the control data of Fig. 6, the latter being from the transmitter transmitted in a sideband of the carrier frequency;

Fig. 9 is a logic flow diagram showing the operation of the receiver portion of Fig. 8; and

FIG. 10 is a pictorial representation of a control panel and display for the receiver of FIG. 8. FIG.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In an embodiment of the invention shown in Fig. 1, an alarm system 11 according to the present invention is provided for use in conjunction with the conventional siren and light devices of emergency vehicles A and B (e.g., police, fire or ambulance vehicles) , In an alternative embodiment, the alarm system may be used with stationary devices such as traffic signs or outside warning sirens, as described in more detail below. In another alternative embodiment, the invention is concerned with applications to vehicles other than emergency vehicles, such as school buses.

A particular aspect of the embodiment of Figure 1 is the transmission and reception of emergency data between the emergency vehicles A and B over a frequency F & sub1; and transmitting supplementary emergency data from the emergency vehicles A and B to the receiver 17 over a frequency F 0, the latter providing the motorized (or fixed location) public with a warning of potential emergency situations. In this way, motorists in the immediate vicinity, or those in fixed locations, can receive warning information from the emergency vehicles.

According to one embodiment of the invention, the alarm system 11 includes a transceiver 13 located in a first emergency vehicle A for receiving RF signals at a first frequency F & sub1; to one or more other emergency vehicles B, which are also equipped with a similar transceiver 13 ', to reduce the risk of collision in emergency situations to a minimum. According to another aspect of the invention, the alarm system also includes a transmitter 15 for receiving an emergency RF signal at a second frequency F & sub0; to a conventional receiver 17, which during its normal operation receives RF signals transmitted on commercial bandwidths. Preferably, a sideband (SB) of this second RF signal uses the standard of the "United States Radio Broadcast Data System" (RBDS) provided by the "National Radio Systems Committee" established by the Electronics Industry Association (EIA) and the United States "National Association of Broadcasters" (NAB) was drafted. The receiver 17 is compatible with the RBDS standard for the purpose of changing the mode of operation of the receiver to an emergency mode when receiving the sideband. The details of this standard and its implementation are set forth in the specification of the "Radio Broadcast Data System" published by the EIA and NAB in 1992 and entitled "United States RBDS Standard, January 8, 1993". Of course, for use outside the United States, the appropriate standard should be used for the country in which the system is used - for example, the European Radio Data System (RDS) standard established by the European Broadcasting Union. An example of such an RBDS compatible receiver having a single input circuit is a Denon Model No. DCT-950R available from Denon Corporation of 222 New Road, Parsippany, New Jersey 07054.

In general, RBDS provides for transmission of digital information encoded in a sideband of a carrier frequency for a normal FM (or AM) voice and music channel. As will be discussed below, the digital information is decoded depending on the exact hardware and software of the receiver 17 and either displayed on a display of the receiver 17 or interpreted as a command signal for controlling the operation of the receiver. For example, control signals transmitted in the sideband may turn on the receiver 17 or tune it to other frequencies (for supplemental weather or traffic information). A front panel of an exemplary RBDS receiver 17 is shown in FIG. In its outward appearance, the receiver 17 differs from conventional commercial RF receivers primarily by its larger alphanumeric display 332 and the RDBS control buttons 38.

In order to transmit information in accordance with the RBDS standard, the digital information appears in the third harmonic (subcarrier) of the 19 kHz "pilot tone" for stereo broadcasts in the 87.5 to 108.0 MHz FM band. (During mono broadcasts, the frequency of the coded subcarrier is 57 kHz). Digital information is encoded in this subcarrier as an amplitude modulated signal and shaped by biphase encoded data signals using the difference encoding scheme following a protocol set forth in the RBDS standard. The energy of the data signal at and near the subcarrier is minimized by encoding each source data bit as a biphase signal. There is a binary signal shaping filter (not shown) to form the band limiting spectrum and the timing and frequency spectrum of the biphase encoded radio data signals.

The result of this frequency coding in the transmitter 15 and the subsequent frequency decoding in the receiver 17 is a stream of binary coded data as shown in FIG.

The data stream is formatted in groups, each data group comprising 104 bits of data. The 104 data bits of each group are divided into four words of 26 bits each. The first 16 bits of each word are the information word, and the last 10 bits are the check bits for the word. Blocks 3 and 4 are generally used to send information to be displayed to receiver 17, while blocks 1 and 2 are normally omitted to provide receiver control command or control information.

For example, blocks 1 and 2 may contain program operating code (PS code). The PS code lets the receiver 17 know that the block 3 contains the calling letters of the transmitting station which should be displayed on the display 332.

In addition to displaying the call letters, the RBDS standard also causes the display 332 to display the program format of the station - for example jazz, rock, classical, etc. The program format is identified by a program type code (PTY) which has up to 31 categories , Categories 30 and 31 of the code are reserved in the RBDS standard for the display of "Test" (# 30) and "Alarm" (# 31) on the alphanumeric letter display 332 of the receiver 17 (see Figure 10). It is contemplated that the present invention will use category 31 of the PTY code as part of its features, as will be explained in more detail below.

Turning now to the schematic illustration in FIG. 1. There, each of the two emergency vehicles A and B is equipped with the alarm system 11 according to an embodiment of the present invention. In the following, the alarm system 11 of this first embodiment will be described with reference to the emergency vehicle A and the operation of this system together with the complementary alarm system installed in the emergency vehicle B. Those skilled in the art will understand that the following discussion, while referring to the alarm system 11 built into the emergency vehicle A, is also applicable to the alarm system built into the emergency vehicle B. Furthermore, those skilled in the art will appreciate that any number of emergency vehicles equipped with the alarm system 11 may cooperate within the scope of the present invention to provide emergency warnings. Corresponding devices in the emergency vehicles A and B are identified by the same number. In order to distinguish between the two systems, however, the numbers identifying the alarm system of the vehicle B and its components are written canceled - ie 11 ', 13', 15 'etc.

Via the antennas 19a and 19b, the transceiver 13 of the alarm system 11 transmits radio information to the alarm system 11 'installed in the emergency vehicle B and receives radio information therefrom. In the illustrated embodiment, the transceiver 13 radiates at a frequency F & sub1; which is within the bandwidth allocated for emergency use - for example, bandwidth for the police.

In the present invention, the effective range of the antennas 19a and 19b and the sensitivity of the receiver portion of the transceiver 13 'in the alarm system 11' of the emergency vehicle B mutually complement each other, so that the emergency vehicle B alarm system replaces the RF transmitted from the emergency vehicle A alarm system Signal detected when the two vehicles are at a predetermined distance from each other - for example, 457.2 m (500 yards). In this way, the transceivers 13 and 13 'of the emergency vehicle A and B, respectively, transmit signals on the frequency F 1 which are intended to warn other emergency vehicles of their presence when they are in the vicinity of these other emergency vehicles, so that the risk of a collision is reduced. In this regard, the transceiver 13 has only local coverage.

Referring to Fig. 2B, a single dipole antenna A1 substantially produces an omnidirectional characteristic (i). An omnidirectional characteristic of the RF warning signal from the transceiver 13 may be most appropriate in open areas or intersections in urban areas. By excitation of two antennas A1 and A2 spatially separated by an appropriate distance, as shown in Fig. 2B, an elongate characteristic (ii) of the radiated RF signal is generated. This characteristic may be appropriate for the transceiver 13 on separate lane roads to warn only vehicles on one side of the freeway. The warning signals transmitted by the transceivers 13 and 13 'may be analog or digital signals using conventional technologies which are decoded by the receiving transceiver as audible or visible information.

By using either the same frequency transmission protocol of frequency F 1, or multiple frequency transmission protocols, simultaneous transmission by multiple vehicles within their mutual range can be achieved. Various technologies are known for simultaneous transmission at different frequencies. Likewise, technologies are also known to operate on the same frequency F & sub1; using different time-division protocol schemes. For example, in a technology for transmission at different frequencies, the frequencies are selected to match the frequencies at which the search receiver expects to find information. An example of a technology using the same frequency is the use of a radio packet technology known to those skilled in the art. Other examples of protocols based on using the same frequency are time-domain multiple access (TDMA) technology and code-domain multiple access (CDMA) technology, both known in the art of RF modulation and transmission. For the transmission according to the invention from emergency vehicle to emergency vehicle, other technologies or protocols may also be suitable. Further details of the aforementioned technologies and protocols and additional possible alternatives can be found in the following works: Telecommunication Engineering, 2nd Ed., By J. Dunlop and DG Smith, Van Nostrin, 1987, ISBN 0-278-00082-7; Wireless Communication Handbook, edited by Gary Breed, 1992, Cardiff Publishing Co. (no ISBN number); and Telecommunication Transmission Systems, McGraw-Hill, 1993, by Robert G. Winch, ISBN 0-07-070964-5.

Let us turn to the mode of operation of the transmitter 15. It radiates a carrier frequency F & sub0; in a local area, for example in a range of 91.44 to 457.2 meters (100 to 500 yards). out. A sideband of the carrier frequency F & sub0; includes encoded information using the RBDS standard, and more particularly category 31 of the PTY code used in the invention to place the receiver 17 in emergency mode. The carrier frequency F & sub0; is frequency modulated in a known manner with an audio alarm or a warning signal (eg voice or siren). As will be understood by those skilled in the art of radio transmission and reception, the transmitter 15 may alternatively transmit an amplitude modulated (AM) signal with one of the sidebands of an AM carrier frequency F o '. contains digitally encoded information using the RBDS standard. The carrier frequency F & ' is amplitude modulated in a conventional manner with an audio signal to warn the receiver 17 within the range of the transmitter 15.

According to the invention, the frequency F & sub0; or F & sub0; ' within the tunable range of the conventional receiver for commercial FM or AM broadcasts. As shown in Figure 2A, a bandwidth approved in the United States by the Federal Communications Commission for commercial FM and AM broadcasts is narrower than the tunable range of the conventional receiver 17. Preferably, the frequency F & sub0; (FM) or F 0 ' (AM) is assigned the role of broadcasting emergency signals and information, and therefore outside the commercial bandwidth, but within the tunable range of the receiver 17. As shown in Fig. 2A, the frequency F & sub0; or F & sub0; ' either next to the top, or next to the bottom of the commercial hand width.

Alternatively, the frequency F & sub0; or F & sub0; ' be located within the tunable bandwidth if space is available in the frequency domain. However, this approach would most likely require that the frequencies F & sub0; or F & sub0; ' have different values ​​in different geographic areas, as a single frequency would not necessarily be available in all geographic areas within the bandwidth. The use of different values ​​for the frequencies F & sub0; or F & sub0; ' does not pose a design problem with respect to the receiver 17 because one of its input circuits (to be discussed below) scans all tunable frequencies while searching for control information in a sideband. Unfortunately, however, the use of this alternative approach prevents the transmitter 15 from being reduced to a single frequency value F & sub0; or F & sub0; ' can be coordinated. Therefore, the frequency F & sub0; or F & sub0; ' preferably a frequency outside the band whose value is fixed for all geographical areas.

The transmitter 15 preferably operates at a frequency F & sub0; of 87.5 (or 108.5) MHz, which is at the lower (or upper) end of the FM transmit range. In the context of the present invention, the category 31 of the PTY code (ie the alert code) of the RBDS standard is transmitted by the transmitter 15 to turn on the receiver 17 and / or to increase its volume. As an alternative to category 31, a new category of the PTY code in the categories 23-29 could be defined; these are categories that the standard has currently kept as reserve. In addition to turning on the receiver 17 (when it is off) and adjusting its volume, the PTY warning code also switches the receiver 17 to the fixed frequency F 0 from the commercial station to which it is tuned. of the emergency vehicle. Alternatively, if the receiver 17 is unable to perform this retuning function in response to the corresponding PTY code, an RBDS Traffic Announcement Identification (TA) code is transmitted and used to command the receiver 17, to which Frequency F & sub0; switch. In yet another embodiment of the receiver 17, upon receipt of the TA code, the volume of the audio signal transmitted by the currently-listened FM station is reduced and mixed with the emergency audio signal. In this embodiment, one of the frequency F & sub0; transmitted emergency signal belongs as a traffic announcement, with the originating from the FM station to which the user, audio signal in the background.

When the transmitter 15 is turned on, the broadcast signal is preferably transmitted at a range that complements the range of the audio and / or visual warning system to which the transmitter is associated. In addition, the range of the warning signal can be changed to adapt to changing conditions. For example, in a vehicle application as shown in FIG. 1 is shown, the power of the transmitter 15 and thus the range of the warning signal with the vehicle speed are changed, as will be discussed below. In one particular embodiment, the range of the warning signal varies from a minimum of 152.4 m (500 feet) at 0 to 22.86 km / h (0 to 15 miles per hour) to a maximum of 762 m (2 500 feet). when the emergency vehicle reaches a speed of 68.58 km / h (45 miles per hour) and more.

In the embodiment shown in Fig. 1, the warning system 11 includes a conventional audio / visual signal radiating apparatus. In the vehicle A, a conventional siren 21 and emergency lights 23 are installed. A controller 25, also of conventional type, provides command signals to the siren 21 and to the lights 23. A bi-directional line 27 connects the controller 25 to a control panel 29, which provides a user interface for the control of the lights 23 and the siren 21. An example of a suitable light device is a VISION ™ warning system manufactured by Federal Signal Corporation of University Park, Illinois. An example of a suitable siren is a SMART SIRENTM manufactured by Federal Signal Corporation of University Park, Illinois. These examples include a suitable controller and control panel according to the illustrated embodiment. The VISION ™ Warning System and the SMART SIRENT ™ are described in US Patent Application No. 08 / 212,266 and US Patent 5,296,840, respectively.

In accordance with an important aspect of the invention, as shown in Figure 1, a controller 31 provides command signals to the transceiver 13 and transmitter 15 in response to signals from a control panel 33 over a bi-directional line 35, or in response to signals from the controller 25 by means of a "remote" line 37, turn on. When the siren 21 and / or the lights 23 are triggered, a signal is provided to the controller 31 by the controller 25 via the "remote" input line 37. Depending on the operating state of the controller 31, as described below, the controller responds to the signal on its "remote" input line 37 by turning on the transceiver 13 and the transmitter 15 to emit RF alarm signals that cause the audio / visual signals of the siren 21 and the lights 23. When the RF alarm signals are emitted, either one or both of the antennas 19a and 19b are energized depending on the radiation characteristic desired for the transceiver 13. Likewise, depending on the radiation characteristic desired for the transmitter 15, either one or both of the antennas 20a and 20b are energized.

The invention may be arranged in several alternative embodiments, some of which are shown in FIGS. 3A to 3D. In each of the embodiments of FIGS. 3A-3C, the alarm system 11 of FIG. 1 includes the transceiver 13 and transmitter 15, or both. For example, in FIG. 3A, the alarm system 11 and 11 'in each of the emergency vehicles A and B includes the transmitter 15 and the transceiver 13, respectively, as shown in FIG. In this embodiment, each of the emergency vehicles A and B alerts both the other emergency vehicle and the receiver 17 in the non-emergency vehicle C when they are within range of the transceiver 13 and the transmitter 15.

In the embodiment shown in FIG. 3B, the on-board system of each of the emergency vehicles A and B includes only the transceiver 13. In this embodiment, each emergency vehicle A and B alerts only other emergency vehicles equipped with a similar type of transceiver 13.

In the embodiment of FIG. 3C, the system aboard the emergency vehicle A or B includes only the transmitter 15 to alert the passenger vehicle C having the receiver 17. Although the illustration in FIG. 3C suggests that the passenger vehicle C is a non-emergency vehicle, those skilled in the art will understand that an emergency vehicle may also be equipped with the receiver 17 and therefore can also receive the emergency signal emitted by the transmitter 15. If the receiver 17 is located at fixed locations such as houses, apartments and the like, it may continue to receive the distress signal as well when the transmitter 15 is within range of the receiver.

Within the scope of the invention, another embodiment of the invention is shown in FIG. 3D which shows various fixed visual or audible alarm systems containing the transmitter 15 for the purpose of providing a complementary RF signal to the RDS compatible receiver 17 of FIG to deliver. In these embodiments, an audio and / or visual alarm system according to the invention radiates from a fixed location. Within the general structure of the embodiment of FIG. 1 The embodiments of FIG. 3D include a controller 31 for turning on the transmitter 15 in response to a remote activation signal from the audio and / or visual system that complements it.

Generally speaking, the architecture of Figure 3D ensures that the signal that activates the visual and / or audible signal also turns on or activates the transmitter 15, which is in physical proximity to the audio / visual system. An example of an audio / visual system that can be combined with the transmitter 15 is a conventional egg, as shown crossing system. Another example is a community warning siren 43 as shown. An example of an external warning siren that can use the RF connection according to the invention is disclosed in U.S. Patent 5,146,508. Yet another example is a school alarm system 45 as shown. The alarm system 45 includes a program system for controlling school bell timing. The system 45 cooperates with the transmitter 15 to turn on the transmitter during programmed pauses and before and after the class hours. According to the invention, persistent traffic signs such as the one shown in FIG. 3D may be connected to the transmitter 15 to continuously transmit an RBDS signal, or to transmit the signal during selected periods of daily, weekly or monthly cycles. Also, portable traffic signs such as the arrow sign 49 shown in FIG. 3D may use the transmitter 15 by turning on the transmitter when the arrow sign is in operation. Of course, the alarm signal and the RBDS codes are tuned to each embodiment.

In a modification of the embodiment shown in Fig. 3C, the emergency vehicle A or B may instead be a school bus 51 or the like, as shown in Fig. 3E. Instead of the transmitter being switched on either manually or remotely as a result of activation of the lights 23 and / or the emergency vehicle siren 21, an embodiment of the invention adapted to the school bus 51 will automatically activate the transmitter 15 aboard the bus in response on the mechanical opening of the stop sign 53, which is articulated in a known manner on the side of the bus. The movement of the mechanical link 52 folds the stop sign 53 from a retracted position, which is flush with the side of the bus 51, to a position extending away from the bus to be visible to other vehicles. The extension of the stop flag 53 also turns on the transmitter 15 to emit an RBDS signal which is decoded by the receiver 17 in an approaching vehicle for the purpose of alerting the occupants of the vehicle to approach the holding school bus 51 , In the embodiment shown, a sensor 54 senses movement of the mechanical link 52 to provide a signal on the "remote" input line 37 which causes the controller 31 to turn on the transmitter 15. The sensor 54 may simply be a switch coupled to the mechanical link 52 for opening the stop sign 53.

Fig. 4 shows a pictorial representation of a typical control panel 33 of the system of one of the emergency vehicles A and B in Fig. 1. The system on board the emergency vehicle includes the transceiver 13, the transmitter 15, the controller 31 and the antennas 19a, 19b and 20a, 20b. The control panel 33 includes an alphanumeric display 55 as well as various warning or indicator lights described below. Although the control panel 33 is preferably installed in the driver's cab in the emergency vehicle A or B to allow the driver to see the display 55, according to the embodiments of FIG. 3D, it may alternatively be installed in a fixed location. Of course, the system according to the invention in its simplest, in the FIG. 3E proposed embodiment, no control panel 33, and the transmitter 15 and / or the transceiver 13 are turned on only by the associated conventional audio / visual system.

In the embodiment of Fig. 4, the controller 31 receives remote, automatic and manual input signals for turning on the transceiver 13 and the transmitter 15. The remote control input line 37 of Fig. 4 comes from the controller 25 of the audio / visual system 232, which the conventional lights 23 and the siren 21 contains. The controller 31 also receives input information about the operating condition of the vehicle from the sensors 231 via automatic input lines 57-63.

Depending on its programming, the controller 31 responds to these various inputs by turning on the transceiver 13 or transmitter 15, or both. For example, in the embodiment shown in FIG. 4, the controller 31 receives an input signal from the park / neutral switch 65 of the emergency vehicle via the line 63, thereby indicating to the controller whether the emergency vehicle is parked or in motion. In accordance with its operating program to be discussed in more detail below, the controller 31 may receive the message at the RBDS frequency F & sub0; change or change in response to a change in state of the switch 65, the emission characteristic. The controller 31 also receives from a compass 67 information describing the direction of travel of the emergency vehicle. This information is encoded and transmitted via the frequency F & sub1; emitted by the transceiver 13. transferred to other emergency vehicles. Via an RBDS code in the sideband of frequency F & sub0; It can also be transmitted to the receiver 17. A change of direction of the vehicle is detected by the controller 31, and the data transmission by the transceiver 13 is updated.

The speed of the emergency vehicle A is monitored by the controller 31 by means of a speed sensor 69 to change the transmission power of the transceiver 13 and the transmitter 15 as described below in connection with FIG. This speed information is used to match the effective range of the transceiver 13 and the transmitter 15 to the speed of the vehicle A. The controller 31 also includes an input 71 for manual activation input. In the embodiment shown, as shown in Fig. 4, the manual input is connected to a foot switch 73 which allows the user of the system to turn on the transceiver 13 and the transmitter 15 for broadcasting.

In operation, the alarm system of Figure 4 operates in one of a variety of alternative modes (e.g., eight). The mode can be manually selected by key presses on a switch 75 on the control panel 33. Alternatively, a change in state of one of the automatic, remote or manual inputs causes the controller 31 to automatically switch to a suitable mode under program control. To inform the user of the current operating mode of the system, a portion of the display 55 may be designated to represent a number from zero (0) to seven (7). According to a predetermined convention, each of the displayed numbers corresponds to one of the eight operating modes of the system 11.

Preferably, one of the modes is a "sleep" mode in which neither the transmitter 15 nor the transceiver 13 is turned on or broadcast. A second mode of operation is the "primary" mode, which is automatically selected when the emergency vehicle is moving. This is detected by the controller 31 from the state of the sensors 65 and 69. The third mode is the "secondary" mode, which is automatically selected when the vehicle is stationary; This is also detected by the controller 31 from the state of the sensors 65 and 69. In one contemplated embodiment, the third mode is reserved for a particular message written at the site of the emergency.

When the system is first turned on, it checks the park / neutral switch 65 to see if the vehicle is stationary or moving and selects the appropriate primary or secondary modes of operation. The operator has the option to select other modes by pressing the "Mode" switch 75.

Let us turn to the switches and displays of the control panel 33. Pressing a transmit (XMIT) switch 77 causes controller 31 to turn on transmitter 15 and transceiver 13, manually initiating transmission of the RF message for a selected mode of operation. In order to cause the user to observe the state of the switch 77, it is illuminated whenever the transmitter 15 is turned on. A second keystroke on the XMIT switch 77 switches off the transmitter 15 and the transceiver 13 as well as the illumination of the switch. An on / off switch 79 makes it possible to turn on and off the power supply of the system from the front of the control panel 33. To alert the user to the state of the switch 79, it is illuminated when the power is turned on. A record / playback switch 85 makes the system suitable for composing special messages. Pressing this button while no other buttons are pressed allows selected pre-recorded messages to be played. Pressing this button simultaneously with a "push-to-pick" (PTT) switch 81 allows a particular message to be recorded. The PTT switch 81 activates a microphone 83 for receiving special audio messages, as will be explained in more detail below. A piezoelectric alarm 87 is activated when the transceiver 13 receives a warning signal from another transceiver so that the operator is informed of the proximity of another emergency vehicle. The signal from the piezoelectric alarm 87 also draws the user's attention to the alphanumeric display 55 for additional information that may have been transmitted. As a further visual indication, an ATTENTION indicator lamp 89 flashes when the system detects a signal from another vehicle.

5 is a block diagram of the controller 31, the transmitter 15, and the transceiver 13. The controller 31 includes a microprocessor portion including a central processing unit ("CPU") 52. The CPU 52 operates conventionally under the control of a program memory 54. As part of the basic architecture, a RAM memory 56 also communicates with the CPU 52 over a bus 57 in a conventional manner. Through the input / output circuit 201, the CPU 52 receives various input signals from the audio / visual system 232, the sensors 231, and the foot switch 73, as explained in connection with FIG. In response to these inputs, the CPU 52 turns on the transceiver 13 and the transmitter 15 according to the modes of the controller 31. In response to receiving digital information on the frequency F & sub1; via the transceiver 13, the CPU provides on a line 60 an output to the display 55, the piezoelectric buzzer 87 and the ATTENTION indicator lamp 89 of the control panel 33. As explained below, the transceiver 13 also drives the speaker 246 when the information is on the frequency F & sub1; in analog format.

The input / output circuit 202 connects the CPU 52 and the transceiver 13 and the transmitter 15 so that the controller 31 can turn on the transmitter and the transceiver and also send and receive digital data, as explained in more detail below. An EEPROM 203 contains a menu of messages intended to be digitally encoded either as RBDS coded signals in the sideband of the carrier frequency F 0 transmitted by the transmitter 15. or as a digital signal received from the transceiver 13 by amplitude modulation of the carrier frequency F & sub1; is broadcast, to be transmitted. The menu is set forth below as TABLE I. TABLE I MENU OF DISPLAYED NEWS

According to the invention, each mode of operation of the system may select one of the messages from each of groups 1, 2 and 3 of the menu. The message selected from group 1 is transmitted by both the transceiver 13 and the transmitter 15. In the receiving system 11. ' For example, the message selected from group 1 is displayed on the first line of three (3) lines of text available on the display 55 '. Likewise, in the receiver 17, the message is displayed on the first of the two lines of text of the display.

Preferably, in each mode of the controller 31, the transmitter 15 and the transceiver 13 emit different messages from the group 2. These are displayed as the second text line in both the receiving transceiver 13 'and the receiver 17. The CPU 52 provides the sender 15 in particular one of the messages A to H from the group 2, which is then displayed as the second text line on the display of the receiver 17. However, as the second line of text to be broadcasted by the transceiver 13, the CPU selects point I of group 2, which is an identification code for the broadcasting vehicle.

Finally, the CPU 52 at the transceiver 13 also provides a message selected from group 3 of the menu for transmission. The message selected from group 3 is displayed on the display 55 'of the receiving system 11' as the third line of text. Since the display of the receiver 17 has only two lines of text, the transmitter 15 emits no message from the group 3.

In one example of the transmission of display data, assume that the CPU in one of the modes of system 11 selects group 1 (B), group 2 (I), and group 3 (H) for transmission over transceiver 13. Obviously, the selection of the Group 3 message part requires a periodic refresh, which the CPU 52 handles in a conventional manner. In the receiving system 11 ', the pointer 55' provides the following text:

FIRE

(ID # #)

SOUTHWEST

In the receiver 17, the first line of text is the same as the first line of text that has been broadcast to the receiving system 11 '. However, the second line of text is selected by CPU 52 from points A to H of group 2. For example, in the previous example, the display of the receiver 17 may look like this:

FIRE

TO THE RIGHT,

if it is assumed that the CPU 52 transmits the point B from the group 2 for broadcast in a RE. DS format in the sideband of the carrier frequency F & sub0; selects.

As shown in Figure 5, an emergency vehicle signal encoder (EVS) 68 of the transceiver receives control and message data in digital format from the CPU 52 to initiate emergency vehicle to emergency vehicle (EV-to-EV) transmission. Any number of conventional coding techniques may be used by the encoder 68. The EVS encoder 68 provides an output to a switch 70 which also receives an analog voice signal from the memory 220, as will be explained in more detail below.

Depending on the state of the switch 70, either digital or analog (audio) signals are passed to the transmitter 204. The state of the switch 70 is controlled by the CPU 52 depending on whether digital data or analog voice messages are being delivered to the transceiver 13. From the transmitter 204, the modulated carrier frequency F & sub1; supplied to a variable amplifier 205. The variable gain amplifier 205 includes a gain control circuit (not shown) under the control of the CPU 52 to apply variable gain to the signal from the transmitter 204. In particular, the gain of the amplifier 205 varies in a functional relationship with the vehicle speed sensed by the speedometer 69 between minimum and maximum values. In one embodiment, the CPU 52 uses a simple linear function between minimum and maximum speeds.

The amplified carrier frequency F & sub1; from the amplifier 205 is provided to a receiver / transmitter switch 112, which connects the output of the amplifier to one or both antennas 20a and 20b, depending on the state of the switch 206. The switch 206 is controlled by the CPU 52 to control the radiation characteristic of the radiated signal F & sub1; to change. Preferably, the state of the switch 206 is determined by the mode of operation of the controller 31.

When the transceiver 13 is in the receive mode, the switch 112 connects the antennas 20a and 20b to an RF receiver 116. Demodulated voice signals are passed from the receiver 116 to an amplifier 207 and then to a speaker 246. Demodulated digital signals are asserted a decoder 148 and then supplied via the input / output circuit 202 to the CPU 52. When the transceiver 13 receives a digital EV-to-EV signal, the controller 31 provides corresponding output signals to the display 55 of the control panel 33 to indicate that received data is being transmitted from another emergency vehicle, as set forth in connection with the TABLE I , At the same time, the dedicated ATTENTION lamp 89 is lit (flashing) and the piezo alarm 87 is sounded to indicate that a signal from another emergency vehicle is being received.

Preferably, the message transmitted by the transceiver 13 for reception by another vehicle is formatted to be displayed on each of the three lines of text available on the display 55. As previously indicated, the message can be divided into three sections. The first section of the message is displayed on the first line of the display 55. This portion of the EV-to-EV message is the same as the message sent from the transmitter 15 to the receiver 17 display. The second line of text displayed by the display 55 is the identification number of the sending vehicle. The third line of text is the direction in which the vehicle is moving. A more sophisticated display on the control panel 33 would allow the full utilization of a "Global Positioning" device 208 shown in FIG. In particular, an image representing the sending vehicle at a location on the display relative to a fixed central location representing the receiving vehicle could be displayed. The circumferential and radial position of the image relative to the central position would provide a simple visual relationship for the user to determine the relative position of the transmitting vehicle relative to the receiving vehicle - ie ahead, left, right or behind. Furthermore, the image could provide directional and velocity information if it were presented in the form of a vector. By overlaying a street and expressway map on the display, a complete visualization of the operation of the transmitting vehicle can be obtained.

To transmit voice or siren signals, an analog memory 220 is addressed by the CPU 52 to output analog siren or voice messages to the transceiver 133 or transmitter 15, or both. Preferably, the analog memory 220 is an ISD1012A / 1016A / 1020A voice recorder / player manufactured by Information Storage Devices, Inc. of San Jose, California. The provisional datasheet for these devices dated February 1992 is hereby incorporated by reference into this specification. Also, U.S. Patents 4,890,259, 4,989,179 and 5,241,494 are concerned with these devices.

According to the invention, the analog memory 220 includes a menu of phrases that may be composed by the CPU 52 into an emergency message broadcast by the transceiver 13 or transmitter 15, or both. An example of a menu of phrases contained in the analog memory 220 and accessible through appropriate addressing by the CPU 52 is listed below as TABLE II.

TABLE II

MENU OF AUDIO MESSAGES

FIRST SECTION SECOND SECTION

MOVE

A police approach Please turn right at the road

B fire department is approaching right drive and stop

C ambulance approaches Carefully drive on

D ambulance is approaching slower

E Stop Now Stop Now

F Please keep left

G Accident ahead, pass carefully

H danger on the street, please

Attention

ARREST

A Police on the street Please turn right at the street

B Fire department on the road Drive right and stop

C ambulance approaches Carefully drive on

D Ambulance on the road Slowing down

E Stop Now Stop Now

F Accident ahead, pass carefully

G danger on the road, please be careful

In operation, voice switch 211 routes the addressed voice sections to one or more of transceiver 13, transmitter 15 and speaker 246, depending on the mode of operation of controller 31. In order to transmit the voice sections via transceiver 13, switch 211 provides the analog Signal to the switch 70 which is controlled by the CPU 52 to supply the analog signal to the input of the transmitter 204. The carrier frequency F & sub1; is modulated by the audio frequencies of the analog voice messages in a conventional manner. From the transmitter 204, the modulated signal from the amplifier 205, the switch 112 and the switch 206 is processed in the same manner as described above in connection with the digital signals from the CPU 52 and the EEPROM 203. The transmitter 204 of the transmitter 13 is turned on by the controller 31 via the line 221.

Depending on the mode of operation of the controller 31, the speech retainer 211 may also direct the analog signal output from the analog memory 220 to the transmitter 15. Depending on the selected mode of operation, the transceiver 13, or the transmitter 15, or both may broadcast audio. The transceiver 13 and the transmitter 15 may also broadcast audio messages that are different from each other. As shown in FIG. 5 The speech sections are supplied to a transmitter or modulator 212 in the transmitter 15, where the carrier frequency F & sub0; is modulated with the audio frequencies of the speech sections in a conventional manner. As with the circuitry of the transceiver 13, the modulated output from the transmitter / modulator 212 is provided to a variable power amplifier 213 to drive the antennas 19a and 19b. Like the variable power amplifier 205 of the transceiver 13, the variable power amplifier 213 of the transmitter 15 has a variable gain whose adjustment is controlled by the CPU 52 by means of the input / output circuit 202 between minimum and maximum values. As with the transceiver 13, a switch 214 responds to the CPU 52 to connect one or both of the antennas 19a and 19b to the power amplifier 213. Preferably, the audio message is repeatedly read from the analog memory 220 and broadcast by the transmitter 15.

According to the invention, an analog or audio signal radiated by the transmitter 15 is also used to transmit an RBDS coding signal in a sideband. In general, the format of the RBDS signal corresponds to FIG. 6, and in particular it corresponds to the parameters of category 31 of the PTY code which has been reserved for "emergency" functions. As described in the RBDS specification identified hereinabove, digital data in an encoder 215 of the transmitter 15 is encoded into an RBDS format. The RBDS encoded data is provided to an amplitude modulator 216 for the purpose of modulating a subcarrier frequency generated by a generator 217. The output of the amplitude modulator 216 is the amplitude modulated subcarrier from the generator 217 in accordance with the RBDS data from the encoder 215. The modulated subcarrier signal is added at summing junction 218 to the analog signal from analogue memory 220. The composite digital and analog signals are then modulated in a conventional manner by the transmitter 212.

Before the controller 31 stops transmission by the transmitter 15, an RBDS coded signal is transmitted, which returns all receivers 17 in the capture range to their previous operating mode. The transmitter 15 is then turned off by the controller 31 by applying the appropriate signal to the transmitter 212 via the line 219. If the RBDS signal intended to terminate the transmission is not received by the receiver 17, it will detect the loss of the transmission frequency F 0. determine and reset after a dead time.

The emergency vehicle operator may change the digital messages transmitted by the transmitter 15 and the transceiver 13 by pressing the "mode" switch 75 on the control panel 33. By holding this instantaneous button in its depressed position, the collection of message choices contained in the EEPROM 203 scrolls over the display 55. When the switch 75 is released, the displayed alphanumeric message is selected for broadcast in the selected mode with any associated audio signal from the analog memory 220.

A particular voice audio signal may be recorded in the analog memory 220 at any time for later broadcast by the transceiver 13 and / or the transmitter 15. To record a voice signal, the operator depresses the record / playback switch 85 on the operation panel 33 and the PTT switch 81, and speaks into the microphone 83. The CPU 52 responds to activation of both buttons by closing the microphone switch 209, allowing analog input to the voice / message memory 220. The operator can check the recorded audio voice signal by pressing the recording / playback switch 85 after the PTT switch is released. If the voice message is acceptable to the operator, the "Mode" switch 75 is pressed, which identifies the message with the selected mode. Pressing the XMIT button 77 then causes the message to be sent. This message replaces any other message sent in the current mode of the system. This new special message is repeated until the system is turned off or the controller 31 receives another input command.

The operator can broadcast a real-time message at any time. Pressing the "PTT" switch 81 places the system 11 in a mode which couples the microphone 83 directly to the transmitter 15. In particular, the CPU 52 turns on the transmitter 15 and provides it with a suitable RBDS encoding data signal intended to gain control of the receiver 17. To ensure that the user of the receiver 17 understands that an emergency voice message is being received, an alert tone is emitted by the transmitter 15 prior to the transmission of the voice message. To alert the user of the system 11 when the system is ready to transmit a real-time message, the display 55 will display the word "LANGUAGE" indicating that the alarm sound has been sent out and the voice channel is available. When the system 11 is in a mode when the PTT switch 81 is pressed, the controller 31 enters the real-time message broadcasting mode.

FIG. 7 is the logic flow diagram of the operation of the controller 31 shown in FIG. 5. As shown there, the CPU 52 is initially powered in step 400 and performs a conventional initialization sequence in step 402 (clear memory, load programs and the like) configuring the hardware and software of the system. The CPU 52 then performs a diagnostic routine in step 404 which checks the operation of the system.

If the diagnostics routine detects an error in step 406, the piezo alarm 87 sounds and an error message is displayed in the alphanumeric display 55 in step 408. The system is then stopped. If the diagnostic routine passes step 406, the CPU 52 then looks in step 410 for an interrupt. If no interrupt is detected in step 410, the system performs a power-down mode in step 416 and waits for an interrupt.

If an interrupt is detected in step 410, the controller 31 first checks to see if it is a serial (remote) function, which is any information transmitted by another emergency vehicle. If this type of interrupt is detected in step 416, the CPU 52 decodes the transmission in step 418 and, in step 420, provides the corresponding visual message by taking any or all of the following actions: flashing the WARNING lamp 89; Sounding the piezo alarm 87; Displaying information on the alphanumeric display 55; and providing an audio message via the speaker 246.

If the interrupt detected in step 416 does not originate from the transceiver 13, the controller 31 considers the interrupt in step 422 as a "local" interrupt generated by the control panel 33, the sensors 231 or the audio / visual system 232. The CPU decodes this local interrupt in step 422, identifies what has changed in step 424, generates a new message in step 426, and executes the message or function in step 428. In one example, the interrupt may have been generated by a state change of one of the sensors 231, the footswitch 73, or the audio / visual system 232. In response to this change of state, the controller 31 may change the mode to emit appropriate RF signals via the transmitter 15 and the transceiver 13. If the interrupt in step 410 is neither serial nor local, the resulting unknown interrupt is again presented to interrupt 410 for further handling. Once the messages 420 or 428 are displayed, controller 31 returns to step 410 for further execution.

Turning to the block diagram of the receiver 17 in FIG. 8. The receiver 17 includes two input circuits 306 and 308, each comprising a tuner and a demodulator. The outputs 310 and 311, respectively, of each of the input circuits 306 and 308 provide an audio switch 312 with an audio frequency signal. In a conventional application, the two input circuits 306 and 308 are tuned to the same radio frequency. Such an arrangement is useful, for example, when the vehicle of the receiver 17 is stopped at a traffic light and the frequency to which the receiver is tuned becomes weak. This dual arrangement of the input portions of the receiver 17 allows the CPU 320 to select the strongest signal from the two input circuits 306 and 308 to maximize the signal strength. The invention advantageously uses the second input circuit 306 under the control of the CPU 320 to monitor RBDS-type broadcasts. Upon receipt of emergency signals on the carrier frequency F & sub0; and its RBDS sideband, the CPU 320 performs the appropriate decoding function. The tuning of this second input circuit 306 need not be fixed to the frequency F & sub0; be set to ensure that the receiver 17 operates according to the invention. For example, the input circuit 306 may scan the FM band for special sideband information. It is important to note that advances in technology could make the second input circuit superfluous; A simple input circuit with very fast search capabilities, or other RBDS features, may in the future enable only one input circuit to be used to perform the functions of the two input circuits 306 and 308.

The central processing unit or CPU 320 of the receiver 17 operates in a conventional manner under the control of a program memory 322. In response to the receipt of emergency RBDS data, the CPU 320 provides 328 outputs to the display 332, the pager driver 330 and an ATTENTION light available. In addition, the CPU 320 controls an audio switch 312 and a CD / tape player 314 that controls the audio signal input to an amplifier 336 and a speaker 334.

In normal operation, commercial channel audio signals are supplied from one of the input circuits 306 and 308 to the audio switch 312. Commercial transmissions are handled as follows: All sideband data is decoded by decoder 316 and sent via line 318 to CPU 320 for execution by program memory 322. Should the sideband data advise the CPU 320 to turn on the lights 328, enable the pager driver 330, or drive the display 332, then these activities are performed. The listener will hear the commercial broadcast over the speaker 334 and see the lights 328 and the display 332 responding to arbitrary sideband data. The user control of the receiver 17 is achieved in a known manner by means of the switches 338.

When the input circuit 306 is at the frequency F & sub0; receives a transmission from the transmitter 15 of the system 11, the decoder 316 decodes the emergency data from the sideband and presents it to the CPU 320 for processing. The CPU recognizes the data under program control as the category 31 of the PTY code (ie the emergency code) and responds accordingly. In particular, the CPU 320 switches the audio switch 312 off its current position (ie Off, input from the input circuit 308 or input from the tape / CD player 314) to an input from the input circuit 306 where the demodulated audio noise signal is present. The amplifier 336 is set by the CPU 320 to a level that has been predetermined as the best for broadcasting the audio distress signal. Depending on the exact nature of the sideband data, the CPU 320 will also drive the display 332 to display information in a text format (e.g. "FIRE, DRIVE RIGHT", see FIG. 10) and activate the pager driver 330 and the lights 328. The pager driver 330 provides a sound, which may be used to announce the transition of the receiver 17 into an emergency mode, to the speaker 334. If the receiver 17 is out of range of the transmitter 15, the CPU controller 320 will Return the system to the normal operating mode it was in before receiving the emergency signal.

9 is a logic flow diagram of the program stored in the program memory 322 of the receiver 17 shown in FIG. 8. The receiver 17 is initially started in step 500, and the CPU 320 performs an initialization sequence in step 502. In the sequence of step 502, the CPU 320 configures the hardware and software of the receiver 17 in a manner well known to those skilled in the art. The CPU 320 then performs a diagnostic routine, step 504, which checks the operation of the system.

If the CPU 320 determines in step 506 that an error has occurred, in step 610 the pager driver 330 is activated to sound an alarm and an error message is displayed on the alphanumeric display 332. The CPU 320 then returns to step 504 and stops. On the other hand, if the diagnostic routine passes step 506, the CPU 320 proceeds to step 508 and determines in step 514 if an interrupt has been received. If no interrupt is detected in step 508, the CPU 320 proceeds to a "power down" mode in step 512 and cycles through the loop of step 508 while waiting for an interrupt.

If an interrupt is detected in step 508, the CPU 320 first determines in step 514 whether the interrupt is an interrupt related to the operation of the receiver according to the RBDS standard, or whether it is a user-generated interrupt for such Work like changing the volume or changing the stations is. If the detected interrupt is a signal from the input circuits 306 or 308, the CPU 320 decodes the transmission in step 518 and determines whether the data is an emergency code or a user-defined code according to the invention. A user-defined code may be a PTY code input via the RBDS switches 38 on the front panel 350 (see FIG. 10), which requires the receiver 17 to search for a station having the same PTY code. If the decoded message is an emergency code (eg, the PTY code 31), the CPU 320 processes the warning signal in step 520. In particular, the CPU 320 connects the input circuit 306 to the amplifier 336 via the audio switch 312. The CPU 320 also controls the display 322, the pager driver 330, and the lights 328, as discussed above in connection with FIG. If the warning function is fully activated, the CPU 320 branches back to step 508 and continues to look for an interrupt.

If the detected interrupt is not an RDS interrupt, the system processes the interrupt in step 516 as a user function. If the interrupt detected by the CPU 320 in step 518 is a user-defined RBDS command, the CPU 320 proceeds to step 522 and processes the user request. The system then returns to step 508 and monitors for further interrupts.

From the foregoing detailed description, it will be understood that the alarm system 11 provides an effective broadcast area which, in the illustrated embodiment, complements the effective alarm area provided by conventional audio / visual systems such as the system 332. By using the RBDS standard, conventional RBDS compliant receivers such as the receiver 17 can be remotely controlled by the alarm system 11 to alert, enhance and supplement the ability of the audio / visual system to alert anyone in the local area. Since the transmitter 15 radiates an RF emergency signal in accordance with the RBDS standard, the receiver of the emergency signal need not have any special equipment to benefit from the improvement provided by the alarm system 11. As suggested by the alternative embodiments shown in FIGS. 3A to 3E, the alarm system 11 may be implemented in the form of several different architectures. In all of these architectures, however, the transmitter 15 supplements an audio / visual system to control RBDS compatible receivers in approximately the same local area as covered by the audio / visual system.