US 3660811 A
A transmitter, carried by an emergency vehicle, transmits directional jamming radiation to operating receivers of passenger vehicles in its path. Different fixed frequency audio signals alternately modulate both an AM carrier and an FM carrier to provide a wobbling sound at either AM or FM receivers. The carrier frequencies are varied through their respective broadcast bands to scan up and down their frequency spectrums so that the alarm is picked up by any receivers in the directional path of radiation regardless of the station to which it is turned. The carriers are caused to scan their broadcast spectrums by imparting reciprocating motion to slugs in inductor tuners in circuit with the respective oscillators, thereby varying the carrier frequencies.
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Description (OCR text may contain errors)
United States Patent 51 3,660,8 1 1 Vail et al. 1 May 2, 1972 s41 PROXIMITY WARNING TRANSMITTER 2,490,591 12/1949 l-limmer ..331/1s1 x FOR EMERGENCY VEHICLES 1,612,427 12/1926 Flurscheim.. .....340/33 UX 2,605,393 7 1952 Holm ..340 34 UX  Inventors: Evelyn W. Vail; John Popik, both of l Columbus Primary Examiner-David L. Trafton  Assignee: Alert, Inc., Columbus, Ga. Attorney-Wilkinson, Mawhinney & Theibault  F11ed: Nov. 12, 1.969  ABSTRACT  Appl' 87s668 A transmitter, carried by an emergency vehicle, transmits directional jamming radiation to operating receivers of pas-  U.S.Cl ..340/33,325/ 132,331/ 181, senger vehicles in its path. Different fixed frequency audio 332/41 signals alternately modulate both an AM carrier and an FM lllt. carrier [o p ovide a sound at either or  Field of Search ..340/32,33, 34,384 E; receivers. The carrier frequencies are varied through their 325/13 11 331/181; 332/41 respective broadcast bands to scan up and down their frequency spectrums so that the alarm is picked up by any receivers in  References Cited the directional path of radiation regardless of the station to UNITED STATES PATENTS which it is turned. The carriers are caused to scan their broadcast spectrums by imparting reciprocating motion to slugs in 2,465,341 3/1949 Altovsky ..325/ 132 X inductor tuners in circuit with the respective oscillators Gossler ....340/34 X thereby varying the carrier frequencies 2,994,765 8/1961 Adam .325/131 X 2,910,688 /1959 Kelley et a1 ..340/384 E 6 Claims, 4 Drawing Figures i 18 g 39011. m 1T 1 AUDIO |2;4-2m1-| NRY y 1 5 1"- osc. 3' 4s 22! 1ooo- 1 H050 L m ri L U a: 1 f o 33 '9 1 37 u fd. +12Vo a' 5 s 5H 5 1 l7 '5 3 0: I 47 j 5 2 g 33 g 1 luf AUDIO U 3 056. L osc. cow-4m 3000- HENRY 'PATENTEDMAY 2:912 3,660,811 SHEET 2 [IF 2 F IG .3 INVENTORS EVELYN W. VAIL JOHN POPIK ATTORNEYS- of vehicles of the proximity of an emergency vehicle in sufficient time to prevent collision.
Not only are a greater percentage of new vehicles being equipped with airconditioning but also the sound-proofing qualities of new cars are being improved. Thus, the greatest hazard is presented to persons riding in those vehicles with the windows closed, either the air conditioning or heating equipment operating and the radio receiver'turned on. Regardless of the mode of receiver operation, i.e. AM or FM, and the setting of the dial, it is the purpose of this invention to develop a warning audio signal at such receivers, which signal jams the entertainment broadcast to alert the driver to the presence of the emergency vehicle. Naturally, this signal will reach only the operating radios within the directional range predetermined for the transmitter, usually a transmission path approximating the width of the street, say fifty feet, and directed ahead of the vehicle for some distance, say 900 to 1,000 feet, as developed from a 2 watt power output, thereby achieving its purpose without causing undue interference to neighborhood entertainment sets.
A relatively inexpensive transmitter fulfilling these requirements may be constructed by employing two or more sources of audio signals at different fixed frequencies for selective or alternate modulation of the AM and FM carriers, by way of a single bistable multivibrator.
The FM and AM carrier oscillators are in circuit respectively with inductor tuners each of which has its reactance changed by the insertion or withdrawal of a magnetic or iron slug. Here, also, a single driving means may be employed to drive both slugs in and out of their respective inductors to cause the carriers to scan their respective broadcast or entertainment spectrums. The varying frequency modulated carriers are respectively amplified in suitable linear amplifiers and applied to broadly tuned resonant'circuits respectively coupled to AM and FM antennas, each partly shielded to provide for directional radiation, generally along a path directly ahead of the emergency vehicle.
With the foregoing in mind, it is among the objects of this invention to provide a proximity warning device effective through the operatingradio receivers of automobiles in the path of emergency vehicles.
It is another object of the invention to provide such alarm? ing for AM receivers, or for FM receivers, or for both simultaneously.
A further object of the invention is the provision of a wobble or warble type audio broadcast signal, through the use of two or more fixed audio oscillators, for modulation onto AM and/or FM carriers.
Still another object is the provision of a bistable multivibrator for selectively applying the different audio signals to an FM, an AM, or both types of carriers to provide carrier modulation.
Yet another object is the provision of a proximity warning transmitter wherein the carrier or carriers are varied in frequency back and forth across their respective broadcast bands.
Another object of the invention is the provision of an emergency warning transmitter equipped with directional antennas for confining radiation to a predetermined path.
The invention will now be described in connection with a preferred embodiment, as shown in the attached drawings, wherein:
FIG. 1 is a circuit diagram of an AM and FM transmitter to be carried by an emergency vehicle,
FIG. 2 is a schematic electromechanical arrangement for varying the frequency of the carriers,
FIG. 3 is a view in perspective of the AM and FM antennas relative to a housing therefor, and
FIG. 4 is a bottom view of the structure of FIG. 3.
Referring now to FIG. 1, the 12 volt vehicle power system is shown as positive terminal 11 and negative terminal 13. A pair of fixed frequency audio oscillators 15 and 17 are connected to positive lead 19 over branch leads 21 and 22 to supply their outputs to a bistable multivibrator 23 over output leads 25 and 27. The multivibrator 23 receives its positive voltage from lead 21 over lead 29 and provides an output over lead 31 to the primary winding 3 of transformer T The secondary winding 35 of transformer T is center tapped to ground at 37, and each end feeds a separate oscillator, shown at 39 and 41.
The upper oscillator 39 is provided to develop the FM carrier, and the lower oscillator 41 produces the AM carrier.
In series with FM oscillator 39, there is connected an inductor tuner L, and an isolation capacitor 43 with the output circuit extending to the voltage divider comprising resistors 45 and 47.
Similarly, in series with the AM oscillator, there is connected the inductor tuner L and these tuners are preferably ganged together, as shown by the dotted line 51. The inductor tuners cause the modulated carriers to scan their respective entertainment broadcast bands, as will be explained-in detail in FIG. 2. The carriers are introduced to their respective RF and IF frequency amplifiers, contained in the integrated circuit 55, which is of General Electric type PA 273A. The amplified outputs are introduced to the broad tuned resonant circuits 61 and 63 for coupling to the FM antenna 65 over output transformer T and to the AM antenna 67 over output transformer 63, respectively.
The values of the various components are given in the circuit diagrams of FIG. 1, and the integrated circuits are identified as follows:
l5-= General Electric audio oscillator type PA 273 set for 1,000 cycles per second.
17 General Electric audio oscillator type PA 273, set for a frequency.of-3,000 cycles per second.
23 General Electric type .IK fiip flop connected as a bistable multivibrator.
39 Cordover type FMM-2.
41 Cordover type WM-S.
55 General Electric type PA 273A amplifier sections.
T 1:4 turns.
T 1:10 turns.
In operation, the fixed frequency oscillators 15 and 17 are alternatively modulated onto the AM and FM carriers at oscillators 41 and 39. It is the change from the 1,000 cycle fixed frequency of oscillator 15 to the 3,000 cycle per second tone of oscillator 17 and back, etc., which causes the audio wobble,
warble, or rising and falling tone in the listeners receiver to inv itiate instant apprehension or alarm.
Next, the FM carrier of oscillator 39 is caused to scan its band, i.e. 88 megacycles to 108 megacycles, because the iron slug 71 (FIG. 2) is caused to move within and without inductor L Similarly, the AM carrier of oscillator 41 is caused to scan its broadcast band of 0.6 megacycles to 1.5 megacycles as the iron slug 73 traverses inductor L The iron slugs 71 and 73 are connected together by rack 75 which carries stops 77 and 79, and is reciprocated by pinion 81 driven over shaft 83 from motor 85.
The stops 77 and 79 operate the fixed toggle switch 87, shown in dotted outline, because it is the same switch as the double throw double pole reversing switch 87, connected between the power terminals 11 13 and motor 85.
When the motor is driven to the full forward position (as shown), the switch blades 91 are spring biassed or toggle closed to the right and the positive lead 11 is extended to the upper lead 93 for the DC motor 85. However, at this time, stop 77 trips the toggle 87 so that the blades 91 are spring biassed or toggle closed to the left, and the negative potential from lead 13 is now extended to motor lead 93, to reverse the movement until stop 79 toggles switch 87. Motor is of the instantly rever'sable type, and the repeated action obtained serves to cause both carriers continually to scan up and down their broadcast bands. Adjustment of the spacing a location of stops 77 and 79 will control the extent of scan, i.e. change of carrier frequencies.
In order that a relatively lower power of eg 2 or 3 watts may suffice for the transmitter of FIG. 1 to avoid undue interference with apartment or home receivers in the vicinity of the emergency vehicle, the antennas 65 and 67 are partially shielded bythe slotted metal cylinders 65 and 67' of FIGS. 3 and 4, thereby directing the radiation forward of the emergency vehicle and in a relatively narrow path. The housing 101 for the antennas may be comprised of fiberglass or the like, and it is bolted or otherwise afiixed to the body of the emergency vehicle (see bolt or screw holes 103 and 105). The antennas 65 and 67. however, are grounded to the metal or frame work of the emergency vehicle and are best supported on top of a fender, toward the forward end of the vehicle.
It should be mentioned that the invention may similarly find application on the waterways or airways, particularlywhen fog or occluding conditions prevail, with appropriate frequency bands taken into consideration, of course, and perhaps broader directional radiations provided. It might also be mentioned that when the tuner passes through the higher police bands or other important bands, the transmitter circuit may be modulated to acceptable side tone only so as to preserve voice communications. Also, it may be possible to interrupt even stereo-type players in vehicles, provided the manufacturers will cooperate by including an inexpensive tone receiver circuit within the amplifier circuits.
What is claimed is:
l. A proximity warning transmitter to be carried by an emergency vehicle for transmission to conventional vehicle receivers comprising, in combination means for generating two conventional carriers of different frequencies; means for modulating one of the conventional carriers with audio signals; means for modulating the other of said conventional carriers with said audio signals but in a different fashion; means for varying the frequency of each conventional carrier throughout a different band of frequencies; and means for transmitting the modulated varying frequency carriers in a like predetermined direction relative to the emergency vehicle.
2. The proximity warning transmitter of claim 1 wherein the means for modulating the conventional carriers comprises two separate sources of different frequency audio signals; and
switching means for alternately applying signals from said separate sources to modulate the conventional carriers and produce detectible audio warble carried by each.
3. The warning transmitter of claim 2 wherein the means for modulating said one conventional carrier comprises amplitude modulating means; the means for modulating said other conventional carrier comprises frequency modulating means; and said switching means comprises bi-stable multivibrator means.
4. The transmitter of claim 1 wherein the means for varying the frequency of said one conventional carrier throughout a band of frequencies comprises an inductor tuner in circuit with the means for generating said one conventional carrier,
which inductor tuner exhibits inductance over the band of frequencies through which said one conventional carrier is varied; a slug for said inductor tuner; means for moving said slug relative to said inductor tuner to change the amount inserted therein, thereby changing the frequency of said one conventional carrier; the means for varying the frequency of said other conventional carrier throughout a different band of frequencies comprises a second inductor tuner in circuit with the means for generating said other conventional carrier. which second inductor tuner exhibits inductance over the band of frequencies through which said second conventional carrier is varied; a second slug for the second inductor tuner; and means mechanicallycoupling said second slug to said means for moving the first mentioned slug to drive said second slug relative to said second inductor tuner to change the amount inserted therein; thereby changing the frequency of said second conventional carrier.
5. The transmitter of claim 4 wherein the means for modulating the carriers comprises two separate sources of different frequency audio signals; and bi-stable switching means for alternately applying signals from said separate sources to modulate the conventional carriers.
6. The transmitter of claim 5 wherein the means for movm g said slugs comprises a reversible drive motor, stop limit switches, and power connections for the motor connected by the stop limit switches to reverse the motor drive, thereby to impart reciprocating motion to the slugs.