Wickord, Robert H. (Laguna Niguel, CA)
Turner, John D. (Torrance, CA)

05/420892

04/08/1975

12/03/1973

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455/341

340/902

F02B1/04; G08G1/0962; F02B1/00; H04B7/00

325/55,64,51,53,466 340/224

Griffin, Robert L.

Libman, George H.

This is a continuation in part of application Ser. No. 179,772, filed Sept. 13, 1971, now abandoned.

We claim

1. A radio warning system operable when required, and including: a radio transmitter means comprised of a modulator and a plurality of independently operable frequency generating means and broadcasting an alert signal on a predetermined frequency; a power amplifier driving a transducer means distantly remote from said transmitter means and a power supply therefor; and a receiving converter comprised of at least a decoder means distinguishing the reception of each of said plurality of frequencies produced by said frequency generating means, a plurality of transducer means and each responsive to reception of a frequency produced by a corresponding one of said frequency generating means, a Radio Frequency section, a local oscillator and interrelated mixer and an Intermediate Frequency amplifier and detector and adapted to be maintained in an on condition from the said power supply and having switching means intermediate the said power supply and said power amplifier and transducer means and responsive to reception of said alert signal to turn on said power amplifier and transducer means, said power amplifier and transducer means being in continuity with the output of the receiving converter Intermediate Frequency amplifier and detector.

2. A radio warning system operable when required, and including: a radio transmitter means comprised of a modulator and a variable frequency generating means and a constant frequency generating means, said frequency generating means being independently operable, said transmitter means broadcasting an alert signal on a predetermined frequency; a power amplifier driving a transducer means distantly remote from said transmitter means and a power supply therefor; and a receiving converter comprised of at least a decoder means distinguishing the reception of said constant frequency produced by said constant frequency generating means, and variable frequency transducer means responsive to reception of said variable frequency produced by said variable frequency generating means, a transducer means responsive to reception of said constant frequency produced by said constant frequency generating means, a Radio Frequency section, a local oscillator and interrelated mixer and an Intermediate Frequency amplifier and detector and adapted to be maintained in an on condition from the said power supply and having switching means intermediate the said power supply and said power amplifier and transducer means and responsive to reception of said alert signal to turn on said power amplifier and transducer means, said power amplifier and transducer means being in continuity with the output of the receiving converter Intermediate Frequency amplifier and detector.

3. A radio warning system operable when required, and including: a radio transmitter means comprised of a modulator and a variable sound frequency generating means and a constant subtone frequency generating means, said frequency generating means being independently operable, said transmitter means broadcasting an alert signal on a predetermined frequency; a power amplifier driving a transducer means distantly remote from said transmitter means and a power supply therefor; and a receiving converter comprised of at least a decoder means distinguishing the reception of said constant subtone frequency produced by said constant subtone frequency generating means, and variable sound frequency transducer means responsive to reception of said variable sound frequency produced by said variable sound frequency generating means, a transducer means responsive to reception of said constant subtone frequency produced by said constant subtone frequency generating means, a Radio Frequency section, a local oscillator and interrelated mixer and an Intermediate Frequency amplifier and detector and adapted to be maintained in an on condition from the said power supply and having switching means intermediate the said power supply and said power amplifier and transducer means and responsive to reception of said alert signal to turn on said power amplifier and transducer means, said power amplifier and transducer means being in continuity with the output of the receiving converter Intermediate Frequency amplifier and detector.

4. A radio warning system operable when required, and including: a radio transmitter means comprised of a modulator and a variable sound frequency generating means and a plurality of distinct constant subtone frequency generating means, said frequency generating means being independently operable, said transmitter means broadcasting an alert signal on a predetermined frequency; a power amplifier driving a transducer means distantly remote from said transmitter means and a power supply therefor; and a receiving converter comprised of at least a decoder means distinguishing the reception of said plurality of distinct constant subtone frequencies produced by said plurality of distinct constant subtone frequency generating means, and variable sound frequency transducer means responsive to reception of said variable sound frequency produced by said variable sound frequency generating means, a transducer means responsive to the reception of each corresponding constant subtone frequency produced by each of said plurality of constant subtone frequency generating means respectively, a Radio Frequency section, a local oscillator and interrelated mixer and an Intermediate Frequency amplifier and detector and adapted to be maintained in an on condition from the said power supply and having switching means intermediate the said power supply and said power amplifier and transducer means and responsive to reception of said alert signal to turn on said power amplifier and transduer means, said power amplifier and transducer means being in continuity with the output of the receiving converter Intermediate Frequency amplifier and detector.

5. A radio warning system operable when required, and including: a radio transmitter means comprised of a modulator and selectively operable automatically variable sound frequency generating means and broadcasting an alert signal on a pretermined frequency; a power amplifier driving a transducer means distantly remote from said transmitter means and a power supply therefor; and a receiving converter comprised of at least a Radio Frequency section, a local oscillator and interrelated mixer and an Intermediate Frequency amplifier and detector and adapted to be maintained in an on condition from the said power supply and having switching means intermediate the said power supply and said power amplifier and transducer means and responsive to reception of said alert signal to turn on said power amplifier and transducer means, said transducer means being comprised of speaker means reproducing the sound produced by said variable sound frequency generating means, and said power amplifier and transducer means being in continuity with the output of the receiving converter Intermediate Frequency amplifier and detector.

6. A radio warning system operable when required, and including: a radio transmitter means comprised of a modulator and selectively operable automatically variable sound frequency generating means and voice modulated sound frequency generating means and broadcasting an alert signal on a predetermined frequency; a power amplifier driving a transducer means distantly remote from said transmitter means and a power supply therefor; and a receiving converter comprised of at least a Radio Frequency section, a local oscillator and interrelated mixer and an Intermediate Frequency amplifier and detector and adapted to be maintained in an on condition from the said power supply and having switching means intermediate the said power supply and said power amplifier and transducer means and responsive to reception of said alert signal to turn on said power amplifier and transducer means, said transducer means being comprised of speaker means reproducing the sound produced by said selected voice modulated sound generating means, and said power amplifier and transducer means being in continuity with the output of the receiving converter Intermediate Frequency amplifier and detector.

7. A radio warning system operable when required, and including: a radio transmitter means comprised of a modulator and a plurality of independently operable audio frequency generating means and having means broadcasting an alert signal on a predetermined frequency; a radio receiver distantly remote from said transmitter means and comprised of at least an Intermediate Frequency amplifier and detector and an audio speaker means therefor; a decoder means distinguishing the reception of each of said plurality of frequencies produced by said frequency generating means, and a plurality of transducer means and each responsive to reception of a frequency produced by a corresponding one of said frequency generating means; a power supply for operating said radio receiver; and a receiving converter comprised of a tuned Radio Frequency amplifier, a local oscillator and interrelated mixer and an Intermediate Frequency amplifier and detector operating at the same frequency as said radio receiver Intermediate Frequency amplifier and adapted to be maintained in an "on" condition from the said power supply and having switching means intermediate the said power supply and said radio receiver and responsive to reception of said alert signal to turn on said radio receiver, the Intermediate Frequency amplifier of said radio receiver being in continuity with the output of the receiving converter Intermediate Frequency amplifier and detector.

8. A radio warning system operable when required, and including: a radio transmitter means comprised of a modulator and a plurality of independently operable audio frequency generating means and having means broadcasting an alert signal on a predetermined frequency; a radio receiver distantly remote from said transmitter means and comprised of at least an Intermediate Frequency amplifier and detector operating at said one predetermined frequency and an audio speaker means therefor; a decoder means distinguishing the reception of each of said plurality of frequencies produced by said frequency generating means, and a plurality of transducer means and each responsive to reception of a frequency produced by a corresponding one of said frequency generating means; a power supply for operating said radio receiver; and a receiving converter comprised of a tuned Radio Frequency amplifier and detector operating at the same frequency as said radio receiver Intermediate Frequency amplifier and adapted to be maintained in an on condition from the said power supply and having switching means intermediate the said power supply and said radio receiver and responsive to reception of said alert signal to turn on said radio receiver, the Intermediate Frequency amplifier of said radio receiver being in continuity with the output of the receiving converter tuned Radio Frequency amplifier and detector.

9. A radio warning system operable when required, and including: a radio transmitter means comprised of a modulator and a variable frequency generating means and a constant frequency generating means, and frequency generating means being independently operable and having means broadcasting an alert signal on a predetermined frequency; a radio receiver distantly remote from said transmitter means and comprised of at least an Intermediate Frequency amplifier and detector and an audio speaker means therefor; a decoder means distinguishing the reception of said constant frequency produced by said constant frequency generating means, and a transducer means responsive to reception of said constant frequency produced by said constant frequency generating means; a power supply for operating said radio receiver; and a receiving converter comprised of a tuned Radio Frequency amplifier, a local oscillator and interrelated mixer and an Intermediate Frequency amplifier and detector operating at the same frequency as said radio receiver Intermediate Frequency amplifier and adapted to be maintained in an on condition from the said power supply and having switching means intermediate the said power supply and said radio receiver and responsive to reception of said alert signal to turn on said radio receiver, the Intermediate Frequency amplifier of said radio receiver being in continuity with the output of the receiving converter Intermediate Frequency amplifier and detector.

10. A radio warning system operable when required, and including: a radio transmitter means comprised of a modulator and a variable sound frequency generating means and a constant subtone frequency generating means, said frequency generating means being independently operable and having means broadcasting an alert signal on a predetermined frequency; a radio receiver distantly remote from said transmitter means and comprised of at least an Intermediate Frequency amplifier and detector and an audio speaker means therefor; a decoder means distinguishing a reception of said constant subtone frequency produced by said constant subtone frequency generating means, and a transducer means responsive to reception of said constant subtone frequency produced by said constant subtone frequency generating means; a power supply for operating said radio receiver; and a receiving converter comprised of a tuned Radio Frequency amplifier, a local oscillator and interrelated mixer and an Intermediate Frequency amplifier and detector operating at the same frequency as said radio receiver Intermediate Frequency amplifier and adapted to be maintained in an on condition from the said power supply and having switching means intermediate the said power supply and said radio receiver and responsive to reception of said alert signal to turn on said radio receiver, the Intermediate Frequency amplifier of said radio receiver being in continuity with the output of the receiving converter Intermediate Frequency amplifier and detector.

11. A radio warning system operable when required, and including: a radio transmitter means comprised of a modulator and a variable sound frequency generating means and a plurality of distinct constant subtone frequency generating means, said frequency generating means being independently operable and having means broadcasting an alert signal on a predetermined frequency; a radio receiver distantly remote from said transmitter means and comprised of at least an Intermediate Frequency amplifier and detector and an audio speaker means therefor; a decoder means distinguishing the reception of said plurality of distinct constant subtone frequencies produced by said plurality of distinct constant subtone frequency generating means, and a transducer means responsive to the reception of each corresponding constant subtone frequency produced by each of said plurality of constant subtone frequency generating means respectively; a power supply for operating said radio receiver; and a receiving converter comprised of a tuned Radio Frequency amplifier, a local oscillator and interrelated mixer and an Intermediate Frequency amplifier and detector operating at the same frequency as said radio receiver Intermediate Frequency amplifier and adapted to be maintained in an on condition from the said power supply and having switching means intermediate the said power supply and said radio receiver and responsive to reception of said alert signala to turn on said radio receiver, the Intermediate Frequency amplifier of said radio receiver being in continuity with the output of the receiving converter Intermediate Frequency amplifier and detector.

12. A radio warning system operable when required, and including: a radio transmitter means comprised of a modulator and selectively operable automatically variable sound frequency generating means and having means broadcasting an alert signal on a predetermined frequency; a radio receiver distantly remote from said transmitter means and comprised of at least an Intermediate Frequency amplifier and detector and an audio speaker means therefor; a power supply for operating said radio receiver; and a receiving converter comprised of at least a tuned Radio Frequency amplifier, a local oscillator and interrelated mixer and an Intermediate Frequency amplifier and detector operating at the same frequency as said radio receiver Intermediate Frequency amplifier and adapted to be maintained in an on condition from the said power supply and having switching means intermediate the said power supply and said radio receiver and responsive to reception of said alert signal to turn on said radio receiver, said receiving converter having a normally open switching means intermediate the radio receiver Intermediate Frequency amplifier input and the tuned Radio Frequency amplifier counterpart of the receiving converter Intermediate Frequency amplifier output and responsive to reception of said alert signal to close, the Intermediate Frequency amplifier of said radio receiver being in continuity with the output of the receiving converter Intermediate Frequency amplifier and detector.

13. A radio warning system operable when required, and including: a radio transmitter comprised of a modulator and selectively operable automatically variable sound frequency generating means and voice modulated sound frequency generating means and having means producing an alert signal on a predetermined frequency; a radio receiver distantly remote from said transmitter means and comprised of at least an Intermediate Frequency amplifier and detector and an audio speaker means therefor; a power supply for operating said radio receiver; and a receiving converter comprised of at least a tuned Radio Frequency amplifier, a local oscillator and interrelated mixer and an Intermediate Frequency amplifier and detector operating at the same frequency as said radio receiver Intermediate Frequency amplifier and adapted to be maintained in an on condition from the said power supply and having switching means intermediate the said power supply and said radio receiver and responsive to reception of said alert signal to turn on said radio receiver, said receiving converter having a normally open switching means intermediate the radio receiver Intermediate Frequency amplifier input and the tuned Radio Frequency amplifier counterpart of the receiving converter Intermediate Frequency amplifier output and responsive to reception of said alert signal to close, the Intermediate Frequency amplifier of said radio receiver being in continuity with the output of the receiving converter Intermediate Frequency amplifier and detector.

BACKGROUND

Those persons who are unaware are those which require alerting and it is these persons which may not have a radio turned on, or if they do have an operating radio it will be tuned onto a broadcasting frequency which exclusively drives the loudspeaker. Heretofore there has been no means to automatically turn on such radios in the case of an emergency or to automatically pre-empt any broadcast that is being received. For example in the case of controlling auto traffic, automobiles are for the most part closed (windows up) with outside noise obscured and with radios therein operating at substantial volume. As a consequence, drivers of regular vehicles, including passenger cars and trucks and buses, can be driving toward a possible collision without the slightest awareness of impending danger. Likewise, the citizenry at their places of residence and business, etc., can be removed from awareness simply by not having a radio or the like turned on. Therefore, the present concept is applicable to autos and places of occupancy by persons to be alerted, and is applicable to said autos and places whether or not equipped with radio or television. The character of transmission of said assigned frequency can vary according to the application thereof; in the case of emergency vehicular protective control, said tramsitter being installed on said emergency vehicle and of limited range; and in the case of general citizenry alerting, said transmitter being installed at a central location and of substantial range.

FIELD OF INVENTION

The wide use of radios throughout the world is without an alerting system associated intimately therewith to serve advantageously at relatively negligible cost. Therefore, it is an object of this invention to provide a practical means for activating a warning device and/or an audio circuit per se or that of an existent radio whether turned on or not, by means of transmitting thereof an assigned frequency with an alerting signal that is relayed so as to be made visible or audible and to pre-empt any other braodcast which may be tuned to.

The possible obscurity of sound from within vehicles has been the cause of serious accidents and it is, therefore, an object of this invention to provide means within the passenger compartment of regular vehicles to alert the occupants therein of the presence of any emergency vehicle operating in the vicinity. Concurrently, it is an object to provide an operating emergency vehicle with a transmitter that activates a receiving converter in the aforementioned vehicles to modulate a speaker in a manner to alert the occupants of impending danger.

The likelihood of a large number of the citizenry being in the presence of deactivated radio receivers has been the cause of unawareness and it is, therefore, an object of this invention to provide means which activates such radios in the case of a general alert throughout an area. Concurrently, it is an object to provide a centrally located transmitter that activates a receiver of converter in the aforementioned places of occupancy to modulate a speaker in a manner to alert the occupants of an emergency situation or the like.

With the use of solid state electronics it is possible to have very low current drain and "instant on" operation of radios and amplifiers, and all of which makes for the feasibility of the warning system hereinafter disclosed which is turned on during the presence and/or occupancy of persons to be alerted. To these ends, therefore, it is an object of this invention to provide a continuously operable radio receiver preferably employing solid state circuitry to advantage and adapted to issue an alert transmitted thereto and interrelated with a general radio broadcast receiver to turn the same "on" in the event of an alert and to pre-empt any broadcast reception thereof; and further to turn the same "off" in the absence of an alert and to permit regular broadcast reception through manual controls.

It is an object of this invention to provide a receiving converter for controlling a radio broadcast receiver at the Intermediate Frequency section thereof to insert therein a modulated signal replacing any Radio Frequency signal normally fed thereto.

It is an object of this invention to provide radio transmission to persons to be alerted, with switching means that activates audio and/or visual warning means while pre-empting the usual operation of a radio broadcast receiver.

It is still another object of this invention to provide radio transmission to persons to be alerted with decoding means that activates discrete audio and/or visual warning means.

It is also an object of this invention to provide radio transmission to persons to be alerted with means compatible with the Intermediate Frequency of a radio broadcast receiver to provide a signal useable by the following detector section and to be amplified and fed to a speaker. It is the Intermediate Frequency that is matched by the receiving converter which characterizes this system.

In view of the foregoing objects, it is a general object of this invention to provide a warning system which is continuously operable in the presence of persons to be alerted, being characterized by a minimized receiver and switch means and decoder means which are preferably solid state for low current drain and which are cooperatively related to a "presence" switch of occupancy to automatically activate the system. By "presence" we mean to include such switches as the ignition switch of a vehicle or the equivalent in the home or office, etc., that is in any place having a radio or television receiver and actively occupied by a person to be alerted.

SUMMARY OF THE INVENTION

The invention will be hereinafter described as it is related to regular vehicles such as automobiles and the like, to operate as a traffic control and/or warning system that will alert drivers to emergency conditions and which will include the operation of emergency vehicles, the existance of road impairments of any such conditions which requires caution. Therefore, it is to be understood that the occupied vehicle may or may not be equipped with a general radio broadcast receiver, is invariably equipped with an enabling device such as an ignition switch, and is also invariably equipped with an electrical system for the operation of lighting and accessories. In the event that usual car radio is absent, then an equivalent amplifier detector is supplied in its place. However, with a usual car radio the broadcast signal is received through an antenna and amplified by the Radio Frequency amplifier and beat with a local oscillator signal in the mixer so as to convert the frequency to a lower Intermediate Frequency which is then amplified and coupled into a Detector circuit in order to retrieve the audio component. Variables arise in the selection of different Intermediate Frequencies by different manufacturers and also in the use of Amplitude Modulation as compared with Frequency Modulation, and all of which are factors taken into account and accommodated in this system. Thus, upon receipt of a warning signal from a transmitter especially provided therefor and broadcasting on an assigned frequency, the general radio broadcast is pre-empted and interrupted temporarily, and prevented from entering through the Intermediate Frequency section of the car radio, and alternately a modulated signal is fed thereto from the receiving converter that characterizes this invention and which is coupled into the Detector section of the said car broadcast receiver. Thus, an alerting signal is inserted and which is then detected by the audio section of the car radio to operate the usual speaker. In carrying out this invention, there is a multiplicity of discrete alerting signals that will be referred to, such as for example, an "emergency" signal, a "caution" signal and a "normal" signal in the absence of any alert. The said "emergency" signal is preferably a high intensity tone of variable frequency simulating a siren accompanied by a constant low frequency tone provided to activate a complementary visual display (a subtone). The said "caution" signal is preferably a subtone of constant frequency which may be accompanied by a live or tape recorded message of impending danger. The said subtones are separated from the said emergency tone and are processed by a decoder means which selectively activates complementary indicator means respectively. Simultaneously with the foregoing, reception of the emergency signal requires operation of the car radio, and a feature of the invention is an enabling switch means which automatically operates the car radio upon reception of said emergency signal in the event that it is not manually turned "on." It is significant that the warning circuitry comes "on" with the ignition key "on," and that the car radio, if the car is so equipped, can be turned "on" manually or by the receipt of an alert signal through the receiving converter, and which pre-empts broadcast reception when the radio is manually or automatically turned to the "on" condition. As a "backup" means, the system includes a display unit having a red "emergency" light, an amber "caution" light and a "normal" green light; all of which are responsive to the condition of the circuitry as hereinabove described.

DRAWINGS

The various objects and features of this invention will be fully understood from the following detailed description of the typical preferred forms and applications thereof, throughout which description reference is made to the accompanying drawings, in which:

FIG. 1 is the plot plan of a typical blind traffic intersection, illustrating the approach of an emergency vehicle and a regular passenger vehicle and both of which incorporate the components of the present invention.

FIG. 2 is an electrical schematic illustrating the transmitter that is carried by the emergency vehicle, or the like.

FIG. 3 is an electrical schematic illustrating a typical radio receiver that is carried by the regular passenger vehicle; while FIG. 3a is an electrical schematic illustrating the electronic components which characterize the present invention.

FIG. 4 is a legend of the symbols used, namely the opened and closed conditions of the various switching circuits.

PREFERRED EMBODIMENT

In the drawings we have shown diagrammatically the fundamentals of a typical stereo car radio R having dual AM and FM channels feeding a common audio section A that powers a pair of transducers or speakers S. Each receiver channel has its own Radio Frequency section RF, its own Intermediate Frequency section IF and its own Detector section D. In accordance with this invention, the Detector sections of both the AM and FM channels can be isolated from their respective RV and IF sections and the signal at either one replaced by insertion of an equivalent signal from the receiving converter X, later described. As shown, this warning system includes, generally, the receiving converter X, switching means Y and a decoder means Z; and all of which are cooperatively combined to control the operation of the car radio R and condition display units a, b and c.

The radio R is conventional in every respect and, as generalized above, has an antenna 10, a ground 11 and a power line 12 from a battery 13. A manually operable on and off switch 14 controls operation of the radio R. The battery is grounded at 15, thereby completing the basic circuitry. Note that the IF section of the AM channel is controlled by lines 16 and 17 which extend to the switching means Y later described.

The automobile involves the conventional electrical circuitry which comprises the battery 13 grounded at 15 and an enabling switch 18 that activates the prime mover of the vehicle (not shown) and other accessories as may be desired. The most common prime mover is the internal combustion Otto cycle engine which requires an ignition system involving a coil 19 which is grounded at 20, in which case the switch 18 is referred to as an ignition switch.

Referring now to the source of the alerting signals, this warning system includes an alerting transmission T which is mobile in the emergency vehicle in the preferred embodiment herein disclosed, and stationary in the case of a general area or roadside alerting system. As diagrammed in FIG. 2, the alerting transmitter T is usual in its basic concepts and comprises a crystal oscillator 21 with a buffer and frequency multiplier as necessary, a modulator 22, and a power amplifier 23 that mixes the outputs of said oscillator and modulator and broadcasts the same through an antenna 24. The emergency frequency of the broadcast is to be assigned as circumstances require and will be at a predetermined frequency set aside for this emergency purpose, and in this instance of vehicle traffic control can be of short range capability and consequently of low power output with little chance of interference that would otherwise be adverse. This basic transmitter is specially equipped with one or more alert signal generators and as it is shown it includes an emergency generator E and an encoder oscillator generating either of two selectible audio frequencies SE or SC respectively, the outputs of which feed into the modulator 22 for transmission via the radio frequency carrier. The audio frequencies SE or SC are developed by switching the frequency determining elements, shown as resonant reeds 501 and 502, into or out of the basic oscillator circuit by the position of swich 28, thereby energizing or de-energizing a relay 503. The output of the encoder oscillator is coupled to an input B of the modulator 22 via line 500'; and it can be seen that either SE or SC will be part of the transmitted signal any time the transmitter is in operation. At the receiving end of this system, presence of frequency SE at the input of the decoder means Z will cause the emergency display light a to be turned on; or presence of frequency SC will cause the caution light b to be turned on. The output of emergency generator E is coupled to modulator 22 through multiposition switch 27 and an amplifier 100. Selectible also by switch 27 is the mike 25 and tape player 26 which can be used for either emergency or caution voice messages. In practice, the audible frequency voltage as selected by switch 27 is coupled to a first stage amplifier transistor Q1 by a coupling capacitor C1. The amplified output of transistor Q1 is coupled by a transformer T1 to a second stage amplifier transistor Q2, and the amplified audible frequency voltage is then coupled by a transformer T2 into an input A of the modulator 22. Power is supplied by the voltage appearing on the line marked +DC as referenced to ground -DC when swtich SW1 is turned on. As shown, the other blocks and circuits shown in FIG. 2 are furnished with power by said +DC line.

Emergency generator E comprised of a multivibrator 101 and a voltage controlled oscillator 102 produces two frequencies of oscillations, or it produces a wailing variable frequency oscillators which simulates a siren or other warning sound. The change in frequency generated, rapid or slow, is dependent upon the voltage at the base of a transistor in a circuit between the multivibrator 101 and oscillator 102, there being a network of resistors and capacitors therebetween to vary in the voltage, as shown in FIG. 2. The input to the audio amplifier 100 as selected by the multiposition switch 27 and used to modulate the transmitter T for transmission to the receiving end of this system causes the transducer means S to reproduce the intended alert signal as audible sound. In practice, the multivibrator 101 is "free running" with transistors Q3 and Q4 alternately turning on and off at a rate governed by the circuit values used. When transistor Q4 turns on, diode D1 is reverse biased thereby effectively removing it from the circuit, effecting an open circuit. When transistor Q4 turns off, transistor Q3 turns on and diode D1 is forward biased and provides a closed circuit or current path from ground -DC to +DC as modified by a decoupling filter comprised of resistor R4 and capacitor C4 via resistors R1, R2 and R3. Were it not for capacitors C2 and primarily C3, the voltage would shift abruptly at the junction of resistors R2 and R3 and capacitor C3, and the base of transistor Q5. However, the capacitors C2 and C3 slow down an abrupt change of voltage at the base of transistor Q5, as capacitor C3 charges up through diode D1 and resistors R1 and R2. When transistor Q4 turns on it removes the charge path for capacitor C3 (diode D1 being reverse biased) which discharges through resistor R3 returning the voltage at the base of transistor Q5 toward +DC at a rate dependent on the values of C3 and R3. With different circuit values, a number of unique audible frequencies can be generated by the voltage controlled oscillator as controlled by the multivibrator switching action and related resistor-capacitor network at the base circuit thereof. Transistor Q5 and transformer T3, together with the aforementioned circuit elements, form an oscillator with a basic frequency of oscillation which can be varied (within limits) by varying the voltage on the base of the oscillator transistor Q5, the audible frequency voltage output of which is applied to switch 27 via line e'.

The alerting transmitter T hereinabove described can be operated with an oscillator frequency corresponding to the common IF frequency employed in car radio receivers R, in which case the RF mixer and local oscillator circuits of the receiving converter X hereinafter described can be replaced with simplified amplifier stages necessary, since no conversion of frequency would be needed in order to match whatever IF is used in the receiver R. In other words, it is feasible to assign a common IF frequency to radios, thereby simplifying the equipment of this warning system.

Referring now to the receiving converter X, a partial or complete radio receiver is provided depending upon whether or not the car, other vehicle, home or office to be warned is equipped with a radio receiver R. The receiving converter X is installed in the vehicle to be warned and as shown includes at least an RF section, a local oscillator O and interrelated mixer M, and one or more IF amplifiers (as required). The receiving converter X receives an amplitude modulated signal and operates through the controlled line 17 and AM detector D and audio amplifier section A of receiver R. In the event that receiver R is nonexistent, then the receiving converter X operates directly through a separate detector and audio amplifier A corresponding to the audio amplifier A of the radio R. It will be apparent that the high intensity emergency signal emanating from emergency generator E will dominate the audio output, the subtones being present as background sound.

The switching means Y is provided to pre-empt any broadcast reception tuned in to receiver R and thereby mutes the radio reception insofar as general radio broadcasts are concerned, and enables the receiver R to operate if in the manually off condition; and is shown as a carrier operated switch actuated directly by the received carrier, after amplification by the receiving converter's RF and IF sections. Accordingly, the switch can vary in design and is shown in FIG. 3a as a transistorized circuit that operates a relay 31 to an actuating position closing enabling contacts 32, 33, 34 and 39 while opening a contact 37 which normally closes a circuit to the "normal" light c. switch contact 32 is in parallel with manual switch 14 to thereby enable or energize the radio R when the relay is activated. The contact 33 is in series with the output of the IF amplifiers of converter X to thereby forward the reception thereof via line 17 to the RF section of radio R. The contact 34 is in series in line 16; to a relay 29 that pre-empts the control switching of radio R so as to switch on power to the AM and audio sections thereof in the event that the manual switching is on to the FM section, and to inhibit or pre-empt AM broadcast reception by closing contact 30 to ground; and to a relay 29' that pre-empts the volume control use of the audio section A of radio R so as to produce a calculated volume condition certain to alert the driver of the auto, or to reach the ears of any person within an expected range from the speakers S, and to simultaneously activate the decoder means Z through line 34'. The contact 39 is in series through a latching means L that governs the switching means Y so as to prevent or to minimize "falsing on" of the means Y and also to prevent early "dropping out" or automatic "reset" due to varying signal strengths. In practice, a manual reset switch 38 is provided in addition to the automatic latching means L next to be described. Relay 31 is actuated to accomplish the foregoing by switch means 31' responsive to the output of the IF amplifier of the receiving converter X as governed by the latching means L, and thus the AM IF and audio section A of the receiver R processes the alert signals passed through the receiving converter X.

From the foregoing it will be seen that switching is provided to adapt a radio to this system, either a simple Am receiver or an AM-FM receiver as shown. In the case of the AM-FM stereo receiver illustrated, we control it to our bidding, the FM detector being disconnected from the audio amplifier section when relay 29 is energized. Both audio amplifier channels are used separately for FM and are used in parallel for AM (the audio signal from the AM detector drives both). In the alert mode the low frequency tone to the detector is picked off the bottom channel (see A') through contacts on relay 29', although both channels have the signal and either one could be used. The AM section of the receiver has an AM RF & converter block, an AM IF and an AM detector circuit (see FIG. 3). With relay 29 deenergized it can be seen that the AM-FM switch (part of the car radio) applied power to the AM section of the radio when the switch is in the AM position (lines marked power "A" and power "B" from swtich 14). Likewide, the line marked power "C" supplies power to the FM section when the AM-FM switch is in the FM position. Upon receipt of an alert signal relay 29 is energized and modifies the AM-FM switch functions so that no matter what the position of the switch, power A and C are off while power B is on thereby activating the AM IF and AM detector circuits. Power A and C being off, no AM or FM broadcast signal will get through the radio, however the alert signal at the same frequency as the AM IF signal will be handled by the car radio as though it were a normal signal presented to it, an alert signal coupled into the AM IF circuit via line 17.

The latching means L is provided to govern the switching means Y so as to hold relay 31 closed despite variations and short lapse in the signal strength out of the receiving converter X. When the receiving converter receives an on frequency signal, relay 31 is activated and initiates an alert condition operation of radio R. A time constant means TC is in the latch circuit 39' to permit switch means SCR thereof to turn on only after a given time of sampling a turned on condition of either emergency a or caution b light. In other words, a latch condition occurs only after an on channel signal with a proper subtone is received. Means L will not latch upon reception of short bursts of interference, even when accompanied by a correct subtone frequency. Upon reception of the proper signal, the alert condition of operation of said radio R is now locked in, since contact 39 cannot open because switch means SCR turns on transistor switch TL which puts a latch on relay 31 thereby eliminating any possible drop out due to momentary loss of signal from the emergency vehicle enroute to the scene of an emergency. After the emergency vehicle has passed or the distance from a roadside caution transmitter T has sufficiently increased enough to cause the signal strength to reduce to a predetermined value that will no longer hold an emergency light a or b on by means of a decoder tone (next to be described), a transistor TR turns on and thereby initiates operation of timer 40 (adjustably preset) which times out and resets relay 31 causing the receiving converter X to automatically restore the radio and indicator light c to their normal conditions.

The alert receiver: can be a configuration as shown wherein a transmitted signal of a frequency other than the frequency of the receiver (broadcast) intermediate frequency is received and converted to that frequency by a mixer and a local oscillator (XTAL OSC) circuit, so designed to be at the same as and acceptable to the IF amplifier of the broadcast car radio; or, it can be a straight tuned radio frequency (TRF) amplifier of sufficient gain to operate the carrier operated relay 31, in which case the assigned transmitter frequency of the alert system would be identical to the assigned intermediate frequency of all car radios, e.g., 455Khz with no conversion necessary. In either case, a signal at point X will be acted upon by the following amplifier (IF amplifier) and coupled to the RF carrier detector. The amplifier signal is supplied to the RF carrier detector where it is rectified to produce a DC voltage across capacitor C, a portion of the voltage being used via line L to turn on the first switching transistor 31" which furnishes current amplification to turn on switching transistor 31' used to apply a ground to relay 31 thereby energizing it. When relay 31 is energized contacts 39 close applying voltage to the latch circuit via line 39'. This circuit does not respond to the one input only, since it requires an alert signal to energize relay 31, and thus it can be assumed that either a caution or an emergency tone was detected and lamp a or b turned on. In either case, line 800 is made +DC by diode D1 or D2 as the case may be, and this second input to the latch circuit starts the following action: a Silicon Controlled Rectifier SCR is turned on turning a transistor TL, applying a latch voltage to transistor 31' via line L' at the same time a voltage is applied to SCR 40 and to the UJT. The voltage on line 800 also holds transistor TR in the off condition as long as a transmitted alert-signal is being received. Therefore, assuming the alert signal is shut off (either fades out due to distance or is actually shut off in the emergency vehicle) there is a latch voltage on the base of the transistor 31' via line L' furnished by transistor TL which is held on by the turned on SCR so that the relay 31 remains energized and the receiving converter awaits a signal. If the signal just faded due to intervening buildings or interference and it comes back, then the lamp a or b will again be turned on. If as above, the alert signal is turned off or is out of range and not to come back for a given time, the voltage on line 800 is removed as the lamp a or b goes out. With no voltage on line 800 transistor TR is turned on applying a voltage to point R thereby charging timing capacitor Ct. When the voltage across Ct is raised to a level high enough to fire the UJT (this is the delay while awaiting the signal to come back) the UJT fires turning on SCR 40 which effectively puts a short across line L' removing the latch voltage at the base of transistor 31'. Since no signal is being received by the alert received then the output of the RF carrier detector is zero as is the voltage on line L. This means that there is not voltage on the base of the transistor 31' and it is turned off removing the ground to relay 31, deenergizing it. The car radio then reverts back to its original state before the original alert was received.

The manual reset switch is preferably a foot switch on the floor of the car so that once alerted the driver can press and hold it down so as to return the car radio to the program to which it is tuned. If switch 38 is released before the alert transmitter is out of range, then the car radio would again be captured thereby.

Referring now to the decoder means Z and the condition display units a and b operated thereby, if the signal through receiving converter X and the indicated portions of broadcast receiver R contains the expected audio frequencies SE or SC, then either the emergency a or caution b light is turned on by the output of a transistor A' of the audio section A, through a contact relay 29' via line 34' to a low pass filter means 110 at the input of the decoder thereafter amplified and applied to the frequency sensing circuits 35 and 36 shown as resonant reeds that detect the presence of either low audio frequency SE or SC produced by the encoder oscillator. Present at the output of transistor A' of audio section A during receipt of a warning signal is the low audio frequency SE or SC as well as the audio frequency selected by the multiposition switch 27. These selected audio frequencies are essentially higher in frequency when applied to the input of decoder means Z and are stopped from entering by low pass filter means 110 which only allows the low frequencies in the range of SE and SC to pass through to be amplified by first stage transistor amplifier 111, the output of which is further amplified by second stage transistor amplifier 112 until capable of driving the coils of resonant reeds 35 and 36. Only if the resonant frequency of either reed is present (SE or SC) will the reed vibrate, closing the circuit to and turning on transistor switch 35' or 36' to an indicator light lamp a of b. When transistor switches 35' or 36' are activated they also apply an input to latch circuit L via diode D1 or D2 and line 800. It will be noted that power to the decoder means Z is furnished only when a warning signal is being received, thereby conserving power during normal periods. This is accompanied by using the same switched source as that used to control the broadcast receiver upon receipt of a warning signal.

From the foregoing it will be seen that this warning system is automatically implemented and put into operation simply by turning on a presence switch such as the ignition switch of the vehicle in which the driver is to be warned in cases of emergency or when caution is required. Further, the equipment is automatically activated to mute or pre-empt regular broadcasts and to replace the same with the emergency signal, in both audio and visual form. Removal of the alerting broadcast will release the equipment for "normal" reception by the radio receiver R and a corresponding indication by conditions light c. Given a predetermined assigned frequency for all radios equipped for this radio transmitted warning system, a "home" or "car" switch located, for example, at the alerting transmitter T will determine whether or not the home radio reception will be interrupted. This is, the home radio ned not be unnecessarily interrupted. Thus, the carrier operated switch of the present invention is adapted to be operated by the unique subtone which is selectively called as required, whereby a general alert transmitter is useable to alert all radios.

Having described only typical preferred forms and applications of our invention, we do not wish to be limited or restricted to the specific details herein set forth, but wish to reserve to outselves any modifications or variations that may appear to those skilled in the art.