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Publication numberUS3041507 A
Publication typeGrant
Publication dateJun 26, 1962
Filing dateJul 28, 1958
Priority dateJul 28, 1958
Publication numberUS 3041507 A, US 3041507A, US-A-3041507, US3041507 A, US3041507A
InventorsRobert P Crow, Walter A Kelley, Samuel W Rose
Original AssigneeMotorola Inc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Mobile door control
US 3041507 A
Abstract  available in
Images(2)
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Claims  available in
Description  (OCR text may contain errors)

S. W. ROSE ETAL MOBILE DOOR CONTROL June 26, 1962 Filed July 28. 1958 2 Sheets-Sheet 1 .e u .C r m m KW m m w% m m an 9m mm n mm W W J a a wfiwgw mm 3 \NN MN +v,\%\1 RN June 26, 1962 s. w. ROSE ETAL MOBILE DOOR CONTROL 2 Sheets-Sheet 2 Filed July 28, 1958 INVENTORS. Samuel ZUJZose. fiobert 1. Q7021).

Nun g M mww United States Patent 07 nols Filed July 28, 1958, Ser. No. 751,327 7 Claims. (Cl. 317-149) This invention relates generally to remote control apparatus, and more particularly to a mobile remote control system for opening a garage door from within an automobile or like vehicle.

Various types of automatic garage door controls are known. Some of these employ an electric eye or some other device which actuates a door operator mechanism by sensing the vehicle as it passes a fixed point. Other known control devices require that the driver manually operate a fixed actuator which is not readily accessible from the inside of the vehicle. Such systems have been found to be inflexible and somewhat inconvenient.

It is believed that a door control system using a mobile transmitter and fixed receiver which permits the driver to actuate the door operator mechanism from within the vehicle at a selected point in the approach path is more desirable. In a system of this type, the mobile transmitter should be capable of withstanding strains and shocks imposed by bad roads and exposure to the weather. The receiver must be reliably responsive to signals transmitted from different distances and angles of approach, and yet must be unresponsive to spurious signals.

Accordingly, it is one object of the invention to provide a new and improved mobile door control system of rugged construction and which provides reliable operation.

Another object of the invention is to provide a remote door control system including a transmitter unit of weather-resistant construction which can !be readily installed in an automobile or other vehicle.

Another object of the invention is to provide a remote door control system including a receiver unit of a contruction which is easily adjusted to permit reception of signals from various different angles of approach.

A further object of the invention is to provide a remote door control system including a receiver circuit which provides reliable actuation of a door operator mechanism and protects against spurious responses.

A feature of the invention is the provision of a mobile remote control transmitter unit which is completely embedded in a tough, durable molded material except for a metallic mounting base which permits easy installation on an automobile.

Another feature of the invention is the provision of a remote door control receiver unit having a rotatable loop antenna whose position can be readily adjusted to accommodate reception of signals from various approach angles.

A further feature of the invention is the provision of a reflex action circuit for a remote door control receiver including a differential detector coupled to an output amplifier for developing a control voltage in response to the output signal supplied by the amplifier, and for defining certain frequency limits for the output signal such that the control voltage can exceed a threshold level only when the output signal is within the frequency limits. The control voltage is fed back to control the output current of the amplifier, and a relay whose coil is connected in the output circuit responds to a predetermined change in the output current.

The invention is illustrated in the drawings in which:

FIG. 1 is a schematic drawing showing an automobile 3,041,507 Patented June 26, 1962 .and garage equipped with a mobile door control system in accordance with the invention;

FIG. 2 is a structural drawing partly broken away showing the transmitter unit of the system of FIG. 1;

FIG. 3 is an end view of the transmitter construction of FIG. 2;

FIG. 4 is a circuit diagram for the transmitter unit of FIGS. 2 and 3;

FIG. 5 shows a rotatable loop antenna attached to the receiver unit of the system of FIG. 1; and

FIG. 6 is a circuit diagram for the receiver unit.

The invention consists of a new and improved mobile door control system including a transmitter which may be mounted in an automobile, truck, or the like vehicle, and which is connected to the vehicles electrical system through a switch on the dashboard to facilitate actuation by the driver. Signals are radiated from the transmitter to a receiver which is connected to a door operator mechanism mounted in the garage for the vehicle. The components of the transmitter are mounted on a frame, and nearly the entire structure is embedded in a molded composition which provides effective protection against shock and weather. The antenna for the receiver is rotatably mounted on the outside of the receiver housing so that it can be positioned properly with respect to the orientation of the transmitter antenna in the normal approach path to the garage. The receiver circuit preferably includes first and second amplifier stages coupled in series, and connected to a differential detector which controls the second amplifier stage by reflex action. The second amplifier stage is coupled to a relay which actuates the door operator mechanism. The differential detector is frequency selective and applies a control voltage to the second amplifier stage, the polarity of which is dependent only on the signal frequency. The received signal must be within predetermined frequency limits, regardless of signal level, in order to make the control voltage be of proper polarity to boost the second amplifier stage output current sufficiently to energize the relay. Further protection against spurious actuation is provided by a delay network so that a steady on-frequency signal is required for actuation. An automatic gain control voltage may also be applied from a portion of the detector to the first amplifier to stabilize the response of the detector to signals over a wide signal level range.

In FIG. 1 there is shown schematically an automobile 10 and a garage 11 equipped with a mobile door control system including a transmitter unit 12 and a receiver unit 13. The receiver 13 controls the motor =17 of a door operator mechanism 14 to open or close the door 16 in response to signals from the transmitter 12.

The transmitter 12 is mounted on the automobile in a relatively unobstructed location, preferably under the lead 21 through the dashboard-mounted switch 22 to the battery-generator voltage source 23 of the automobile. Ground connection is provided through the frame of the automobile, and fusing is provided to protect the battery against wiring shorts.

The receiver 13 may be mounted on a joist 24 in the garage, and is connected by a cord 26 to a power supply receptacle inthe door operator machanism 14. The start ing circuit for the motor 17 of the operator mechanism is connected to the receiver 13 by the lead 27. The receiver 13 is provided with a rotatable antenna 15 which is posiltioned properly with respect to the orientation of the transmitter '12 as will be explained further. The details of the construction of the door operator mechanism 14 are believed to be unimportant to the invention and so are not described herein. Operator mechanisms of variass-1,

a ous constructions which are available may be employed with the system of the invention.

The construction of the transmitter unit 12 is shown in greater detail in FIGS. 2 and 3. The transmitter is provided with a metal mounting base 31 which has flanges 28.with apertures for receiving mounting bolts or screws. Attached to the mounting base is a metal supporting frame 30 consisting of a center plate 32 and end plates 33 and 34. The various components of the transmitter including transistor 63 and the antenna are attached to this frame. The frame 30 and mounting base 31 may also provide a ground return for the transmitter circuit, or a ground lead extending to the outside of the unit may be provided. The frame 30 and the attached components are completely embedded in a shock resistant casing 37 of a tough and durable molded material such as filled polyester resin. Portions 29 of mounting base 31 are bent over to engage the sides of the casing for added rigidity. The conductor 38 extends through the casing 37 and is connected through the switch 22 to the battery-generator 23.

An opening 39 is provided in the casing to permit access to the screw 41 for adjusting the antenna core 36 to set the frequency of the radio control signals. The core 36, preferably of ferrite, is composed of two sections 42 and 43 separated by a tapered helical spring 44 which holds the section 42 at the end of a sleeve 46 and biases the section 43 against the adjustment screw 41. The spring 44 is coated with flexible insulating material to prevent the turns of the coils from being shorted when the spring is flattened, and insulating discs 45 are placed on each end of core section 42. The head of screw 41 is guided by a tubular portion of guide 40 which extends from the sleeve 46 to the outside of the casing 37, and the plug portion 50 of guide 40 has threads which engage those of screw 4-1. Coils 4-7 and 48 are wound around the outside of the sleeve 46 to provide coupling to the antenna core 36.

A circuit diagram for the transmitter unit 12 of FIGS. 2 and 3 is shown in FIG. 4. The transmitter includes a transistor oscillator 60 coupled to the antenna core 36 by coils 47 and 48. A capacitor 61 is connected across the coil 47 to form a tank circuit 62 whose series resonant frequency is set in the very low frequency band--that is, between 17.6 kilocycles and 29 kilocycles. The frequency may be set at different points within this band for different units so that if more than one system is installed in the same locality there will be no interference. The frequency of the transmitter can be adjusted over a substantial portion of the band as previously explained so that no circuit changes are required to accommodate the transmitter to several different receiver units. Different ranges within the band require minor variations in the values of the antenna winding and the capacitor 61. B4- is applied through switch 22 and coil 48 to the transistor 63 and is also applied to the tank circuit 62. The resistors 71, 72 and 73 form a voltage divider which biases the base 67 negatively with respect to the emitter 66 and biases the collector 68 negatively with respect to the base 67. The resistor 71 may be a thermistor to provide temperature compensation, and the capacitor 69 bypasses signal frequencies.

When the switch 22 is closed, oscillations in the coil 48 are inductively coupled to the tank circuit 62. The coupling from coil 48 to coil 47 is of the step-up type. Since the tank circuit 62 is in resonance, there is a resonant rise of current through coil 47. Of course, it is possible to eliminate coil 47 and place a capacitor with a larger value than capacitor 61 across coil 48. However, by tuning. the coil 47 a relatively small capacitor may be used and a higher coil Q is possible such that a greater number of ampere-turns is obtainable, and this increases the. induction field strength. The signal is inductively coupled from the core 36 to the receiver antenna 15 as illustrated schematically in FIG. 1.

In FIG. there is shown a portion of the receiver unit 13. The antenna structure 15. includes a ring 51 of insulating material such as a plastic having a tubular portion 52 in which the coil 53 and core 54 are mounted. The ring 51 is rotatably supported in a bearing 56 so that its posi- 5 tion can be readily adjusted. For instance, if the longitudinal axis of the transmitter antenna core 36 is lengthwise of the automobile andthe approach path for the automobile is straight into the garage, the ring '51 should be adjusted perpendicular to the front of the garage 11.

10 If the longitudinal axis of the antenna core 36 is perpendicular to the length of the car, then the ring 51 should be adjusted parallel to the garage 11. If the approach path of the automobile is not straight into the garage, the position of the ring 51 can be adjusted to compensate for the angular deviation from a straight path.

The circuit for the receiver 13 shown in FIG. 6 includes amplifier stages 77 and 88, a relay 121, and a differential detector 111. The radio control signals are picked up by the antenna 15 including core 54 and coil 53 which is tuned by the capacitor 76. 13+ is supplied from the power source 98 to the plate 83 of pentode tube 81 through resistor 87, and is supplied to the plate 93 of pentode tube 91 through resistor 1M shunted by the coil of relay 121, and coil 102. Received signals within the bandpass of tuned circuit 55 are coupled to the first amplifier stage 77 by a capacitor '78. The received signal is applied to be control electrode 82 of tube 81, and the output appears on the plate 83. Bias is applied to the cathode 84 by the resistor 85 connected to ground and bypassed by the capacitor 86.

The output of the amplifier stage 77 is coupled into the second amplifier stage 88 by the capacitor 89. The signal is applied to the control electrode 92 of tube 91, and the output appears on the plate 93. Bias is applied to the cathode 94 by the resistor 95 coupled to ground and bypassed by capacitor 96. The bias on the cathode 94 is held at a relatively fixed level by the resistor 95 and a resistor 97 connected to the power source 93.

The differential detector 111 is coupled to the plate 93 of the second amplifier stage 88 to control the output of the receiver which is applied to the relay 121. The contacts 122 of the relay are connected to the starting contacts 123 for the motor of the door operator mechanism shown in FIG. 1 so that when the relay 12 1 is energized the motor starts.

The differential detector 111 includes an impedance network ltlt) consisting of resistor 1M, paralleled by the coil of relay 121, and tuned circuit 104, and also includes a pair of oppositely poled diodes 112 and 113 connected n in series between the input side of network 100 and ground. The coil of relay 121 functions as an R.F. choke for the operation of the differential detector, and has an impedance at the operating frequency that is high compared to that of resistor 101. The coil of relay 121 therefore has a negligible eifect on the impedance of network 1%, while still passing most of the DC. platecurrent. A resistor 115 is connected across diode 112, and a resistor 116 is connected across diode .113; Capacitor 107 couples diode 112 and resistor 115 to the input side of 6 network 100, and capacitor 106' couples diode 113 and resistor 116 to the junction. between resistor 1131 and tuned circuit 164. The output of the detector 111 is filtered by the resistor 136 and capacitor 114.

When the plug 99 is inserted in an alternating current receptacle which may be provided on the door operator mechanism, B+ is applied to the tubes 81 and 91 as previously explained so that the receiver will be responsistor 101 for the desired signals, and consequently, the voltage developed across circuit 104 is high as compared to the voltage across resistor 101. The voltage developed across tuned circuit 104 is applied to diode 112, and this diode recti-fies the signal voltage to produce a positive voltage at the junction of resistor 136 with respect to ground. The voltage developed across resistor 101 is applied to the diode 113, and this diode rectifies it to a negative voltage across resistor 116 with respect to ground.

A control voltage which is the difference between the voltages produced by diodes 112 and 113 is provided by the filter network 120. When an on-frequency signal is received, the positive voltage produced by diode 112 exceeds the negative voltage produced by diode 113 so that the net voltage is positive. When an off-frequency signal is received, the impedance of the tuned circuit 104 drops so that the impedance thereof is less than that of resistor 101. Accordingly, the voltage across the tuned circuit will be less than that across resistor 101, and the negative voltage produced by diode 113 exceeds the positive voltage produced by diode 112 so that the net voltage at the filter 12th is negative. The control voltage from filter 120 is applied through resistor 135 to the control grid 92 of the tube 91 to provide a bias to control the output current of this tube. When a positive voltage is provided by the on-frequency signal, the output current is increased and is sufficient to activate relay 121, the coil of which is connected in the output circuit of tube 91 and which carries most of its current. When a negative voltage is applied to the grid 92, the output current is reduced sufficiently to prevent energization of relay 121. This reflex action through tube 91 permits simplification of the circuit with reduction in the number of components required and consequent reduction of costs.

Thus, the change in impedance of the tuned circuit 164 of network 100 with change in frequency determines fre quency limits within which the control signal will cause energization of the relay and outside of which the control signal tends to inhibit energization of the relay. This control characteristic is not affected by variations in the strength of signals which are outside the frequency limits. On broadband background noise, equal but opposite outputs are obtained from the two diodes providing a net zero output such that the current in the output tube is not affected by random noise. The control characteristic is further stabilized by an automatic gain control applied to amplifier 77 which will now be explained.

The negative voltage produced by diode 113 is applied through filter 132 to the control electrode 82 of tube 81 to provide automatic gain control of the first amplifier stage. Filter 132 includes resistors 127, 128 and 129 and capacitor 130. When a signal within the bandpass of the antenna circuit is received, the detector 111 provides a negative voltage to cut down the gain of amplifier 77. This feature tends to 'make the response of the receiver independent of the strength of the desired radio control signal, and therefore makes the receiver respond reliably regardless of variations in the distance between the automobile and the garage when the signal is trans mitted. As the voltage across diode 113- is less when an on-frequency signal is received, the gain will be reduced less for desired signals than for undesired signals to improve the frequency response of the system.

The control voltages applied to amplifiers 88 and 77 are respectively delayed in time by the filters 120 and 132 so that a fairly steady on-frequency signal is required to energize the relay.

Thus, the system of the invention provides a rugged and reliable garage door control. The transmitter unit should have a long useful life because of its simple and sturdy construction. The rotatable antenna on the re- 'ceiver unit permits adjustment to accommodate different angles of approach to the garage. The circuits for the transmitter and receiver are quite simple, and yet are adapted to accommodate transmission and reception of signals at different points in the vehicles approach path while rejecting spurious signals of any strength.

We claim:

1. A mobile door control system for actuating an operator mechanism provided at a garage having a power source to control a door of the garage from a vehicle having an electric power source, said system including in combination, an induction transmitter including oscillator means having transistor means and loop antenna means coupled to said transistor means, a voltage supplying circuit coupled to said transistor means and said antenna means and adapted to be coupled to the power source of a vehicle, said loop antenna means including coil means and a ferro-magnetic core therein, means coupled to said coil means forming a resonant circuit therewith for controlling the oscillations of said oscillator means at a predetermined low frequency, said coil means cooperating with said core to generate from said antenna means a high strength induction field for transmission of control signals at said low frequency, said transmitter being adapted to be mounted on the vehicle in a fixed position so that said induction field has a predetermined directional characteristic with respect to the vehicle, and an induction receiver for location in the vicinity of the garage door to actuate the operator mechanism, said receiver having a loop antenna adapted to be provided at the garage in a position establishing optimum inductive coupling between said antenna means of said transmitter and said antenna of said receiver during the approach of the vehicle to the garage door, thereby accommodating different angles of approach, said receiver including a voltage supplying circuit adapted to be connected to the power source of the garage for energizing said receiver, a relay adapted to be connected to said operator mechanism for actuating the same, amplifier means coupling said loop antenna of said receiver to said relay for translating said control signals andfor supplying current for energizing said relay, said amplifier means including a plurality of series coupled stages with the last stage of the series having an output portion at which said signals are developed, differential detector means coupled to said output portion of said amplifier means for selecting signals within predetermined frequency limits and developing therefrom a differential control voltage, and a reflex circuit coupled between said differential detector means and one stage of the series in said amplifier means for applymg said control voltage to said amplifier means to control the current supplied therefrom to said relay, said relay being responsive to a predetermined change in such current to actuate the operator mechanism.

2. A mobile garage door control system for actuating a door operator mechanism provided at a garage having power supply means for operating the mechanism in response to signals from a vehicle having electrical supply means, said system including in combination, an induction transmitter including a mounting base for attachment to a mounting surface in the vehicle, frame means on said mounting base, oscillator means including a plurality of circuit elements supported by said frame means, said circuit elements including transistor means and loop antenna means coupled to said transistor means, a voltage supplying circuit coupled to said transistor means and said antenna means and adapted to be coupled to the supply means of the vehicle for energizing said oscillator means, said antenna means including coil means, a ferromagnetic core positioned within said coil means, and capacitor means coupled to said coil means forming a resonant circuit therewith for controlling the oscillations of said oscillator means at a predetermined low frequency, said coil means cooperating with said core to generate from said antenna means a high strength induction field for transmission of control signals at said low frequency, said core being adapted to be mounted on the vehicle in a fixed position so that said induction field has a predetermined directional characteristic with respect to the vehicle, and a molded casing of insulating material completely embedding said frame means and said circuit elements supported thereby for protecting the same against shock and weather, an induction receiver adapted to be located in the vicinity of the garage door for actuation of the operator mechanism, said receiver having a loop antenna adapted to be provided at the garage in a position establishing optimum inductive coupling between said antenna means of said transmitter and said antenna of said receiver during the approach of the vehicle to the garage door, thereby accommodating different angles of approach, said receiver including a voltage supplying circuit adapted to be connected to the power supply means of the garage for energizing said receiver, a relay adapted to be connected to said operator mechanism for actuating the same, amplifier means coupling said loop antenna of said receiver to said relay for translating said radio signals and for supplying current for energizing said relay, said amplifier means including a plurality of series coupled stages with one stage in the series having a control portion effective to control the energizing current for said relay, and with the last stage in the series thereof having an output portion at which said control signals are produced, differential detector means coupled to said output portion of said amplifier means, said differential detector means including first and second unidirectional circuit paths each including rectifying means, an im pedance network providing an impedance ratio for said rectifying means which varies with the frequency of the received signals, said differential detector means being responsive to receive control signals within fixed frequency limits to develop a control voltage exceeding a reference level, and a reflex circuit coupled between said differential detector means and said control portion of said one stage of said amplifier means for applying said control voltage to said amplifier means to control the current supplied to said relay, said relay being responsive to a predetermined change in such current to actuate the operator mechanism.

3. Induction control apparatus for actuating a door operator mechanism provided at a garage having a power supply means, and which operates in response to control signals transmitted from an induction transmitter mount ed on a vehicle, said apparatus including in combination, an induction receiver adapted to be located in the vicinity of the garage door for actuation of the operator mechanism, said receiver having a loop antenna adapted to be provided at the garage in a position establishing optimum inductive coupling between the transmitter on the vehicle and said antenna of said receiver during the approach of, the vehicle to the garage door, thereby accommodating different angles of approach, said receiver including a voltage supply circuit adapted to be con nected to the power supply means of the garage for energizing said receiver, a relay adapted to be connected to said operator mechanism for actuating the same, amplifier means coupling said loop antenna of said receiver to said relay for translating said signals and for supplying current for energizing said relay, said amplifier means including a plurality of series coupled stages with one stage in the series having a control portion effective to control the current supplied to said relay, and with the last stage in the series thereof having an output portion at which said control signals are produced, differential detector means coupled to said output portion of said amplifier means, said differential detector means including first and second unidirectional circuit paths each including rectifying means, an impedance network providing an impedance ratio for said rectifying means which varies with the frequency of the received signals, said differential detector means being responsive to received control signals within fixed frequency limits to develop a differential control voltage exceeding a reference level, and a reflex circuit coupled between said differential detector means and said control portion of said one stage ti of said amplifier means for applying said control voltage to said amplifier means to control the current supplied to said relay, said relay being responsive to a predetermined change in such current to actuate the operator mechanism.

4. An induction receiver and control apparatus for a door operator mechanism provided in a garage which has an electric power source for operating a door of the garage in response to oscillatory control signals transmitted from an induction transmitter, said apparatus including in combination, loop antenna means adapted to be provided at the garage in a position establishing effective inductive coupling between the trans mitter and the receiver and control apparatus, a voltage supplying circuit adapted to be connected to the power source of the garage for energizing said apparatus, a relay coupled to said voltage supplying circuit and adapted to be connected to said operator mechanism for actuating the same, amplifier means coupling said loop antenna means to said relay for amplifying the oscillatory signals from the transmitter and for supplying a direct current output for energizing said relay, said amplifier means including a plurality of series coupled stages each connected to said voltage supplying circuit and each including an amplifying electronic device, with one stage of the series having a control portion effective to control the energizing current for said relay and with the last amplifier stage in the series thereof having an output portion at which said control signals are developed, differential detector means coupled to said output portion of said last amplifier stage for converting the control signals thereat to a direct current control voltage, and a reflex circuit coupled between said differential detector means and one stage of said amplifier means and supplying said control voltage to said control portion of said one amplifier stage for controlling the direct current gain of said amplifier means and thereby controlling the direct current output supplied to said relay from said amplifier means, said relay being responsive to a predetermined change in such direct current output to actuate the op erator mechanism.

5. An induction transmitter adapted to be connected to a power source and operated from an automotive vehicle to provide control signals for a door control system, said transmitter including in combination, transistor means, loop antenna means coupled to said transistor means including coil means and a ferro-magnetic core positioned in said coil means, means forming a resonant circuit coupled to said transistor means tuned to sustain oscillations at a predetermined low frequency value, a voltage supplying circuit adapted to be coupled to the power source, with said transistor means being coupled to said voltage supplying circuit and responsive to voltage supplied thereby to develop a sustained oscillating induction field in said antenna means for providing control signals for the door control system.

6. An induction transmitter for use in an automotive vehicle having an electrical system to provide control signals for a mobile door control system, said transmitter including in combination, a mounting base for attachment to a mounting surface in the vehicle,tframe means on said mounting base, oscillator means capable of providing sustained oscillations and including a plurality of circuit elements supported by said frame means, said circuit elements including transistor means, loop antenna means coupled to said transistor means including coil means and a ferro-magnetic core in said coil means, capacitor means coupled to said coil means forming a resonant circuit therewith for controlling the frequency of said oscillator means, said coil means cooperating with said core to generate from said antenna means a high strength induction field for transmission of signals of a predetermined low frequency, a voltage supplying circuit coupled to said transistor means and to said antenna means and adapted to be coupled to the electrical system of the vehicle for supplying energizing voltage to said transistor means, and a solid molded casing of insulating material completely embedding said frame means and said circuit elements supported thereon for protecting the same against shock and weather, with said mounting base available on the exterior of said casing for mounting the transmitter in the vehicle.

7. An induction transmitter circuit for a transmitter unit adapted to be connected to a power source and operated from an automotive vehicle to provide control signals for a mobile door control system, said transmitter circuit including in combination, transistor means, loop antenna means including coil means coupled to said transistor means and a ferro-magnetic core positioned in said coil means, capacitance means connected to said coil means and forming a resonant circuit therewith tuned to generate an induction field in said antenna means of a predetermined low frequency, means connecting said resonant circuit to said transistor means to sustain oscillations thereof, and a voltage supplying circuit including biasing means coupled to said transistor means and adapted to be coupled to the power source for supplying energizing voltage to operate said transmitter unit.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Publication, Radio and Television News, February 1954, pages -38 and -132.

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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3147000 *Jul 31, 1961Sep 1, 1964Honeywell Regulator CoControl apparatus
US3207959 *Dec 8, 1961Sep 21, 1965Western Electric CoMiniaturized and transistorized frequency selective amplifier circuit
US3233239 *Jul 17, 1961Feb 1, 1966Motorola IncInduction field transmitter
US3333272 *Apr 1, 1963Jul 25, 1967Cons Electronics IndNarrow bandwidth receiver with output equal to the voltage difference of a selected modulation frequency and all frequency voltages
US3359558 *May 18, 1964Dec 19, 1967William A SchanbacherReceiver arrangement
US3497995 *Apr 19, 1968Mar 3, 1970Stanley WorksHeight sensitive proximity door operator system
US5177900 *Aug 23, 1991Jan 12, 1993Solowiej Henry EAutomatic pet door
US5379453 *Jan 18, 1994Jan 3, 1995Colorado Meadowlark CorporationRemote control system
US6021319 *Nov 14, 1994Feb 1, 2000Colorado Meadowlark CorporationRemote control system
WO2000058587A1 *Mar 29, 2000Oct 5, 2000Estevez Contreras Jose ManuelSystem for the connection of portable radiofrequency emitters to the electric circuit of a motor vehicle
Classifications
U.S. Classification361/182, 49/25, 340/5.71
International ClassificationE05F15/20
Cooperative ClassificationE05F15/2076
European ClassificationE05F15/20E