Radio Signal Initiated Remote Switching System

Abstract

A radio signalling system includes a transmitter operating to transmit a continuous carrier signal periodically modulated with a tone signal burst. A receiver includes an amplifier-detector operating to recover the audio tone signal bursts, which are then amplified, threshold detected, and converted to corresponding output pulses. A discriminator, responding to the amplifier-detector output, enables a gate only during the intervals between tone signal bursts when unmodulated carrier is received. The output pulses are passed by the enabled gate and accumulated to ultimately effect triggering of switching means to initiate a remote switching function. Energization of the transmitter is achieved by selectively positioning a pivotally mounted battery to make an electrical contact between a battery terminal and a stationary terminal contact.

Description

BACKGROUND OF THE INVENTION

It has become extremely important and desirable in our modern technological society to be able to actuate and/or control all types of apparatus from a distance. This can be accomplished in many ways; however, one of the more practical ways is to use a radio signal link between a receiver coupled to the apparatus and a portable transmitter. Radio signal initiated remote switching systems can be advantageously used, for example, to actuate security or burglar alarm systems, conveyor belts, etc., from remote locations. Currently such systems are in wide use to actuate powered garage door openers from inside an automobile.

Prior art radio signal initiated remote switching systems have however been subject to certain operational difficulties. One of the most serious problems is phantom operation; that is, accidental or inadvertent actuation of switching apparatus by stray noise signals. Such accidental or inadvertent actuation can be quite serious and even dangerous, especially when heavy equipment such as conveyors or garage doors are involved. With the current wide use of portable radio transmitters and other electrical or electronic equipment, the atmosphere is replete with electromagnetic noise energy, and thus the possibility of phantom operation is ever present.

To avoid phantom operation, transmitters have been designed to transmit variously coded signals which must be successfully decoded by the receivers before the switching function will be carried out. Such signal codings usually involve various techniques of discretely modulating a radio frequency (RF) carrier signal so that only a receiver equipped with the proper demodulating or detector stage can respond. Many of the proposed solutions to phantom operation are so complex and expensive as to be wholly impractical. Moreover, some designs are so sensitive as to reject a proper actuating signal if it is only slightly distorted or masked by noise. In locations where noise signals are prevalent, it can be extremely difficult to initiate the switching function even when it is desired to do so.

It is accordingly a general object of the present invention to provide a radio signal initiated remote switching system which is adapted to prevent the initiation of phantom switching functions while, at the same time, to readily initiate a switching function when desired upon reception of a true or proper signal. A further object is to provide a system of the above character which is efficient and reliable in operation, simple in design, compact in size and inexpensive to manufacture.

Other objects of the invention will in part be obvious and in part appear hereinafter.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a transmitter which is energized when it is desired to initiate a remote switching function. The transmitter is adapted, when energized, to generate a continuous carrier signal which is periodically modulated with a tone signal burst. As a consequence, the signal transmitted by the transmitter is in the form of alternating bursts of tone signal modulated carrier and unmodulated carrier.

The receiver of the present invention includes an amplifier-detector tuned to the carrier frequency and operating to recover from the carrier signal the bursts of tone signal. A filter-amplifier, connected to the output of the amplifier-detector, amplifies only those tone signals received from the amplifier-detector which are of a predetermined frequency corresponding to the frequency of the tone signal originated at the transmitter. Thus, the receiver is tuned to respond only to a particular companion transmitter which together make up one system of the invention.

The uniformly time spaced bursts of amplified tone signal are supplied to a threshold detector which responds only to amplified tone signal bursts exceeding a predetermined amplitude level. The receiver therefore rejects at this point any signals, although of the proper frequency, which are below a predetermined amplitude. In practice, this rejection would discriminate against low level noise signals of the proper frequency and also against tone signal bursts transmitted from beyond a desired signal range.

The response of the threshold detector is translated into an output pulse corresponding to each tone signal burst of the proper amplitude.

A discriminator connected to the output of the amplifier-detector operates in the absence of a received carrier signal and to the presence of noise to disable a gate. The gate in turn acts to inhibit the passage of the output pulses derived from the threshold detector. The discriminator however enables the gate only for the intervals during which an unmodulated substantially noise-free carrier signal is received. During these intervals, the gate passes the output pulses derived from the threshold detector to accumulating means. After a number of output pulses have been accumulated, switching means are triggered to initiate the switching function desired.

In accordance with a feature of the invention the transmitter is provided with a pivotally mounted battery. The transmitter is enclosed in a case which mounts a pushbutton which is depressed to selectively pivotally position the battery so as to achieve electrically contacting engagement between one of the battery terminals and a fixed battery terminal contact, thereby completing the connection of the battery across the transmitter circuit. A spring normally positions the battery to disconnect it from the transmitter circuit when the pushbutton is not depressed.

The invention accordingly comprises the features of construction, combinations of elements, and arrangements of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanied drawings, in which:

FIG. 1 is a block diagram of the transmitter employed in the system of my invention;

FIG. 2 is a detailed circuit schematic diagram of the transmitter of FIG. 1;

FIG. 3 is a block diagram of the receiver employed in the system of the invention;

FIG. 4 is a detailed circuit schematic diagram of a portion of the receiver of FIG. 3;

FIG. 5 is a top plan view, partially broken away, of a case enclosing the transmitter of FIG. 1;

FIG. 6 is a sectional view taken along line 6--6 of FIG. 5; and

FIG. 7 is a sectional view taken along line 7--7 of FIG. 5.

Like reference numerals refer to corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION OF THE INVENTION

The radio signalling system of the present invention includes a transmitter which, as seen in the block diagram of FIG. 1, includes an audio tone signal generator 10 and a periodic pulse gate 12 operating to pass periodic bursts of an audio tone signal for modulating a continuous RF carrier signal generated by a radio frequency generator 14. Thus when the transmitter is energized from a battery 16 by closure of a switch S1, a signal in the form of alternating bursts of tone signal modulated carrier and unmodulated carrier is radiated by an antenna 18.

Referring to the detailed receiver circuit schematic diagram of FIG. 2, the RF generator 14 consists of a modified Hartley oscillator which includes a transistor Q1. The collector of transistor Q1 is connected to a tank circuit 15 consisting of a variable capacitor C1 and an inductor L1. Capacitor C1 is varied to tune the generator 14 to a desired RF carrier signal frequency ranging preferably from 220 to 320 megahertz. Antenna 18 is connected to a tap on inductor L1, while power is supplied to the RF generator 14 from battery 16 by way of switch S1, an RF isolating inductor L2 and a second tap on inductor L1. Resistor R1 connected between the collector and base of transistor Q1 provides appropriate bias, and capacitor C2 connected across resistor R1 provides the proper phase shift feedback signal for sustaining self-regenerative operation of the RF generator 14 at the carrier signal frequency set by variable capacitor C1. Capacitor C3 connected between the emitter of transistor Q1 and the battery 16 provides AC bypass, while the emitter resistor R5 serves to limit the oscillator current to within appropriate limits.

Still referring to FIG. 2, the audio tone generator 10 includes a transistor Q2 whose collector is connected to the lower end of resistor R5 and whose emitter is connected to the negative terminal of battery 16. Audio tone generator 10 is illustrated as being a phase shift oscillator having a phase shifting network consisting of capacitors C4, C5 and C6, and resistors R2 and R3. Bias for transistor Q2 is provided by resistor R4. Resistor R3 is preferably a variable resistor or potentiometer in order that the audio tone generator may be tuned to a suitable audio tone signal frequency within the range of approximately 8 to 20 kilohertz.

The periodic pulse gate 12 seen in detail in FIG. 2 is in the form of a free-running multivibrator consisting of transistor Q3 and a unijunction transistor Q4. The collector of transistor of Q3 is connected to the lower end of resistor R5, while its emitter is connected to the negative terminal of battery 16. The base of transistor Q3 is connected to the emitter of transistor Q4 by a capacitor C7. Resistor R6 connects the base of transistor Q3 to the positive terminal of the battery, while resistor R7 connects the emitter of unijunction transistor Q4 to the same battery terminal. One base of unijunction transistor Q4 is connected directly to the negative terminal of battery 16 while the other base terminal is connected through a resistor R8 to the positive battery terminal. Resistor R8 serves to temperature stabilize the cycling frequency of periodic pulse gate 12.

The operation of the periodic pulse gate 12 is briefly as follows. Upon the closure of switch S1, power is applied to the periodic pulse gate 12 and the RF generator 14 which begins generating the carrier signal. Current from the battery 16 flows through resistors R6 and R7 and capacitor C7 into the base of transistor Q3, turning this transistor on. As a result, the lower end of resistor R5 is effectively connected to the negative battery terminal through the now low impedance collector-emitter circuit of transistor Q3. The audio tone generator 10 is thus shorted out of the transmitter circuit and does not therefore generate an audio tone signal.

The portion of the base current for transistor Q3 flowing through capacitor C7 charges this capacitor to progressively raise the potential of the emitter of unijunction transistor Q4. When the potential at the emitter of unijunction transistor Q4 reaches a predetermined percentage of the potential across its base terminals, transistor Q4 turns on to effectively connect its emitter to the negative terminal of battery 16 by way of its lower base terminal. Transistor Q3 is then reversed biased and turns off with the result that its collector-emitter circuit becomes a high impedance effective to apply energizing power to the audio tone generator 10. The audio tone generator turns on to effectively emitter-modulate transistor Q1 in the RF generator 14. Thus, during the interval while transistor Q3 of the periodic pulse gate 12 is turned off, the receiver is radiating the RF carrier signal modulated by the audio tone signal.

Capacitor C7 in the periodic pulse gate 12 now charges in the opposite direction through resistor R6 to eventually turn on transistor Q3 and turn off transistor Q4, completing a cycle. While transistor Q3 is turned on, the audio tone generator 10 is de-energized and the RF generator 14 continues to generate and the transmitter continues to transmit the RF carrier signal which, during this interval of the periodic pulse gate cycle, is unmodulated. The cycling rate of the periodic pulse gate 12 is determined by the values of resistors R6, R7 and capacitor C7. A suitable pulse gate repetition rate may be on the order of 200 cycles per second.

It is thus seen that the transmitter in FIGS. 1 and 2 operates during the period of closure of switch S1 to transmit a continuous RF carrier signal which is modulated with periodic bursts of an audio tone signal generated by the audio tone generator 10. The frequency of the RF carrier is determined by adjustment of variable capacitor C1, while the frequency of the tone signal is adjusted by variable resistor R3. The cycling rate of the periodic pulse gate 12 determines the repetition rate of the audio tone signal bursts superimposed on the RF carrier signal.

The receiver of the present invention includes, as seen generally in FIG. 3, a receiving antenna 20 which acts to couple the signal radiated by the transmitting antenna 18 to the input of an RF amplifier-detector 22. Amplifier-detector 22 is tuned to the carrier signal frequency of the companion transmitter with which it is associated in the system. This RF amplifier-detector may take the form of a conventional super-regenerative amplifier-detector which has the advantages of high amplification and high modulation detection combined in a single circuit having very few components. The detected audio tone signal burst, as well as any noise present, is amplified in a conventional audio amplifier 24 whose output on lead 26 is supplied to an audio tone signal processor 28 and also to a tone signal burst and noise discriminator 30. The outputs of the discriminator 30 and processor 28 are applied as separate inputs to a gate 32. Under certain circumstances, which will be detailed in conjunction with the portion of the receiver schematic shown in FIG. 4, the output of gate 32 effectively provides an output to trigger a switch 34 which initiates actuation of a utilization device 36.

Since RF amplifiers and detectors and audio amplifiers are well known in the art, a schematic of these components is not included in the circuit diagram of FIG. 4. While I prefer to employ a super-regenerative amplifier-detector in the receiver of my invention, it is understood that other known RF amplification and detection/demodulation devices may be used.

Referring now to FIG. 4, the output of audio amplifier 24 on lead 26 is directly connected to the base of a transistor Q5 included in the audio tone signal processor 28 and operating as a unity voltage gain power amplifier. The collector of transistor Q5 is connected directly to B.sup.+ and its emitter is connected to ground through an emitter load resistor R10. The output signal at the emitter of transistor Q5 is coupled into an audio tank circuit 37 consisting of capacitors C10 and C11 and an inductor L5. Tank circuit 37 is tuned to the frequency of the audio tone signal generated by the audio tone signal generator 10 (FIGS. 1 and 2) of the companion transmitter; tuning may be accomplished by making inductor L5 a ferrite core inductor whose inductance is readily varied by adjusting the ferrite core in or out. This tank circuit preferably has a high Q so as to provide high amplification as well as high audio tone signal frequency selectivity or filtering.

The audio tone signal in the tank circuit 37 is coupled to the base of a transistor Q6 through a large series resistor R11. Transistor Q6, also included in processor 28, acts as a threshold detector-amplifier. The threshold level which must be exceeded to achieve conduction of transistor Q6 is pre-established at its emitter by a voltage divider consisting of resistors R12 and R13, while its collector is connected to ground through a resistor R14. Capacitor C12 connected from the emitter of transistor Q6 to ground acts as a filtering capacitor for maintaining the threshold operating level of transistor Q6 established at its emitter substantially constant.

As the amplitude of the audio tone signal builds up in the tank circuit 37 to the point where it exceeds the threshold level established for transistor Q6, it breaks into conduction and develops an essentially square wave signal across its collector load resistor R14. This square wave signal, though somewhat delayed, corresponds to the audio tone signal burst supplied to the tank circuit 37. A filtering capacitor C13, connected across load resistor R14, improves the wave shape of this square wave signal. This square wave signal or pulse across load resistor R14 is supplied to the base of a switching transistor Q7 through a resistor R15. The collector of transistor Q7 is connected to B.sup.+ through a resistor R16, while its emitter is connected directly to ground. Transistor Q7 is turned on by each square wave pulse such that its collector goes essentially to ground potential for the duration of each pulse. At the termination of this pulse input, transistor Q7 turns off and its collector rises immediately to B.sup.+ potential. Thus, transistor Q7 provides a pulse output on lead 40 corresponding to each received audio tone signal burst, but slightly delayed in time.

Still referring to FIG. 4, each time spaced audio tone signal burst on output lead 26 of audio amplifier 24 is also AC coupled by a capacitor C14 to the base of a transistor Q8, which is included in the tone burst and noise discriminator 30 of FIG. 3. The emitter of transistor Q8 is connected to B.sup.+ and is normally maintained in a cut-off condition by biasing resistor R17. Capacitor C15 connected between the base and ground provides high frequency roll-off filtering.

When a detected audio tone signal burst is coupled to the base of transistor Q8, it turns on to charge up a capacitor C16 connected across a collector load resistor R18. The DC voltage developed across capacitor C16 is coupled by a resistor R19 to the base of a transistor Q9 included as part of the gate 32 in the receiver block diagram of FIG. 3.

The emitter of transistor Q9 is grounded while its collector is connected to B.sup.+ through a capacitor C17, output lead 40 for transistor Q7 and resistor R16. The collector of Q9 is also connected through a diode D1 and the parallel combination of a capacitor C18 and a resistor R20 to ground. The cathode of diode D1 is connected by a resistor R21 to the base of a transistor Q10, whose collector is connected to B.sup.+ through a resistor R22 and whose emitter is connected to ground through resistor R23. Transistor Q10 is a power amplifier providing an output on lead 44 connected between its emitter and the switch 34. Switch 34 is disclosed in FIG. 4 as a silicon controlled rectifier D2 with lead 44 connected to its gate input. When silicon controlled rectifier D2 is triggered on from the output of transistor Q10, it assumes a low impedance state to, in effect, complete an energizing circuit for the utilization device 36.

Still referring to FIG. 4, it is seen that so long as gate transistor Q9 is turned on from the discriminator transistor Q8, its collector is effectively grounded. Thus no current can flow through diode D1 to charge capacitor C18 and ultimately effect triggering of the silicon controlled rectifier D2 by way of power amplifier Q10. One of the advantages of using a super-regenerative detector 22 is that in the absence of a received carrier signal, it inherently develops considerable noise. This noise output from detector 22 is effective to turn on the discriminator transistor Q8. As a result, the gate transistor Q9 is held in conduction, essentially clamping the anode of diode D1 to ground. This completely disables the receiver circuit from ever achieving spurious or phantom triggering of the controlled rectifier D2. That is, the conductance of the gate transistor Q9 effectively prevents any signal from switching transistor Q7 from ever affecting controlled rectifier D2.

During the time an unmodulated carrier is received by the receiver the output from the audio amplifier 24 on lead 26 goes essentially to zero, assuming the absence of noise. Of course noise, with or without an unmodulated carrier, turns discriminator transistor Q8 on and also gate transistor Q9 to effectively disable the remainder of the receiver circuit. In the absence of an output on lead 26, discriminator transistor Q8 is biased off by resistor R17 and gate transistor Q9 is cut off, to disconnect the anode of diode D1 from ground. No current flows through diode D1 at this point however since its anode remains at ground potential by virtue of capacitor C17 and its cathode is essentially also at ground potential by way of resistor R20.

When a burst of audio tone signal is detected by detector 22, discriminator transistor Q8 is turned on, driving gate transistor Q9 into full conductance. The burst of audio tone signal builds up in the tank circuit 37 to drive threshold detector transistor Q6 into full conduction. Switching transistor Q7 is turned on and its collector goes from B.sup.+ to ground potential. It is seen that while transistor Q7 was non-conductive, capacitor C17 is charged such that the voltage across it is essentially that of the supply voltage B.sup.+ . Due to this pre-existing charge on capacitor C17 a negative-going pulse is produced at the anode of diode D1 when the collector of transistor Q7 goes to ground. This negative-going pulse is blocked by diode D1 and is shunted to ground through gate transistor Q9. At the termination of the audio tone signal burst, transistors Q8 and Q9 turn off since the receiver is now receiving unmodulated carrier signal.

Due to the slight delay in the build-up and decay of the audio tone signal burst in tank circuit 37, the switching transistor Q7 is turned off a short time after the reception of the tone signal burst has terminated and gate transistor Q9 has been cut off (and the gate of which Q9 is part is enabled). Thus when the collector of transistor Q7 goes from ground to B.sup.+ , capacitor C17 is effective to produce a positive-going pulse which is passed by diode D1 and accumulated in storage capacitor C18. The voltage across capacitor C18 resulting from a single such charging pulse is insufficient to turn on output transistor Q10 and fire the controlled rectifier D2.

Upon reception of the next audio tone signal burst, the process repeats and a second charging pulse is passed by diode D1 and accumulated in capacitor C18. The time constant of capacitor C18 and resistor R20 is established such that after a number of charging pulses, for example five, at properly spaced intervals have been accumulated in capacitor C18, the voltage across it becomes sufficient to drive power amplifier Q10 into conduction and thus fire the silicon controlled rectifier D2. If the interval between charging pulses is greater than the interval between modulated carrier bursts, which is indicative of spurious noise reception, the charge leaks off of capacitor C18 through resistor R20 at a faster rate than capacitor C18 is charged through diode D1. In this situation, power amplifier Q10 does not turn on and the silicon controlled rectifier D2 is not triggered.

It is thus seen that the receiver of my invention is amply equipped to guard against phantom triggering of controlled rectifier D2. The receiver must receive a carrier signal of a frequency reasonably close to the center frequency to which the amplifier-detector 22 is tuned. The detected tone signal bursts must have the right frequency (tank circuit 37), have sufficient amplitude (threshold detector Q6), and have an appropriate repetition rate (storage capacitor C18 and resistor R20). In addition the receiver must receive alternate bursts of unmodulated carrier signal and the level of noise signal must be low, otherwise gate transistor Q9 operates to prevent the passage of charging pulses to storage capacitor C18. The probability of all of these conditions being met without reception of a proper signal transmission from the transmitter which is companioned to a particular receiver is very, very low.

By the same token, receivers constructed according to the present invention can be variously tuned to different frequency channels, both in terms of carrier frequency and tone signal frequency, so as to discriminate against all signal transmission except the one from the transmitter which has been correspondingly tuned. Thus, a plurality of transmitters and receivers can operate in the same locale without interference.

The utilization device 36 may take a variety of forms. If the system of the invention is adapted to control the opening and closing of a garage door, the utilization device would typically be a relay controlling the energization of an electric motor. The controlled rectifier D2, when triggered, completes an energizing circuit for the relay which, in turn, controls the motor energizing circuit via its associated relay contacts. The relay energizing circuit may be AC or DC, as controlled rectifiers are suited for either application. The relay may be of the self-latching type such that the controlled rectifier need only be rendered momentarily conductive.

Referring now to FIGS. 5 through 7, the transmitter of FIGS. 1 and 2 is enclosed in a case, generally indicated at 60. The case is formed in two sections 61 and 62 of a suitable molded plastic. The case sections are secured together by a bolt 64 which slides through a sleeve 66 integral with case section 62 and threadedly engages an internally threaded sleeve 68 integral with case section 61, as best seen in FIG. 6.

The various electronic components of the transmitter are mounted on a circuit board 70 which, in turn, is secured by suitable means such as an adhesive between locating ribs 72 in case section 62. Printed circuit board 70 is provided with an opening 74 accomodating extension of sleeve 66 therethrough.

The battery 16 powering the transmitter is pivotally mounted by a bracket 76 secured to the circuit board 70. The ends of bracket 76 are bent upwardly and resiliently engage opposite ends of battery 16 to pivotally mount the battery relative to the printed circuit board 70. As seen in FIGS. 5 and 7, the left end portion 78 of bracket 76 is formed having a dimple 79 struck therein which engages the left end of battery 16. The other end portion 80 of bracket 76 is similarly formed having a dimple 81 which is received in one of the cup-shaped terminals 82 of a conventional 9 volt radio battery 16. Bracket end portion 80 thus electrically engages terminal 82 of the battery 16 and bracket 76 itself is electrically connected to one side of the transmitter circuit. It is seen that dimples 79 and 81 essentially constituting opposed pivot points defining a pivot axis for battery 16.

A second bracket 90 is secured to circuit board 70 and has its right end portion 92, as seen in FIGS. 6 and 7, bent upwardly. Bracket end portion 92 is positioned such that when battery 16 is pivoted downwardly about its pivot axis the other battery terminal 94 comes into electrically contacting engagement with the upper edge thereof. Bracket 90 is electrically connected to the other side of the transmitter circuit, and thus end portion 92 constitutes a battery terminal contact which, when contacting battery terminal 94, completes the connection of the battery across the transmitter circuit to energize the transmitter. The left end portion of bracket 90, indicated at 96 in FIG. 7, is bent upwardly to act as a spring member normally biasing the battery 16 upwardly about its pivot axis such that battery terminal 94 is normally out of electrically contact engagement with contact 92. Thus, the transmitter circuit is normally de-energized.

To energize the transmitter circuit, section 61 of case 60 is formed having a stepped opening 98 which accomodates a pushbutton 100 in overlying engagement with the upper surface of battery 16. It is thus seen that depression of pushbutton 100 pivots the battery 16 downwardly about its pivot axis to make the electrical connection between battery terminal 94 and contact 92.

Thus, by virtue of the pivotal mounting of battery 16 in the case 60 for the transmitter, the transmitter can be turned on and off by selectively manipulating the position of battery 16. This eliminates a conventional on-off switch, which, in mass production, constitutes a significant cost saving.

Throughout the description and in the claims to follow the carrier signal has been characterized as being "continuous." This is intended to mean that the carrier signal is "continuous" relative to the audio tone signal. In certain applications government regulations may limit the duration of carrier signal generation to, for example, 1 second out of every 30 seconds in order to reduce the volume of electromagnetic signal energy in an area. In the context of the instant invention, a 1 second carrier signal duration would encompass, for example, 200 bursts of the audio tone signal, and thus the former is indeed continuous relative to the latter.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A radio communications system for initiating actuation of a device from a remote point, said system comprising, in combination:

A. a transmitter operable to transmit a continuous carrier signal periodically modulated with a burst of a tone signal;

B. a receiver adapted to receive transmissions from said transmitter;

C. a detector in said receiver for recovering said periodic bursts of tone signal from said continuous carrier signal;

D. means for converting each said tone signal burst to a corresponding output pulse and for storing said pulse;

E. a gate connected to control passage of each stored pulse from storage;

F. gate control means connected to the output of said detector for enabling said gate to pass stored output pulses only during the periodic intervals of reception of unmodulated carrier signal;

G. means for accumulating output pulses passed by said gate when enabled; and

H. switching means coupled to said accumulating means and energized thereby when a desired condition of pulse accumulation has been reached to initiate actuation of the device.

2. The system defined in claim 1, wherein

1. said detector is of a type which continuously produces a noise signal at its output in the absence of a received carrier signal, and

2. said gate control means operates to disable said gate in response to either a noise signal or a tone signal burst at the output of said detector.

3. A radio signal initiated remote switching system for actuating a device from a remote point, said system comprising

A. a transmitter operable to transmit a continuous carrier signal;

B. means in said transmitter for periodically generating a burst of tone signal for modulating said carrier signal and leaving intervals when said carrier signal is free of such tone signal modulation;

C. a receiver adapted to receive said periodically modulated carrier signal;

D. a detector in said receiver for recovering said tone signal bursts;

E. a gate circuit in said receiver;

F. a discriminator connected to the output of said detector and to a control element of said gate, said discriminator operating to

1. disable said gate during the absence of a received carrier signal; and

2. enable said gate only during each interval of reception of substantially noise-free, unmodulated carrier signal;

G. means connected to the output of said detector for converting said recovered periodic tone signal bursts into corresponding output pulses;

H. means for receiving each said output pulse and presenting it in stored form for passage through said gate when enabled;

I. means connected to the output of said gate for accumulating said output pulses passed by said gate when enabled; and

J. switching means controlling actuation of the device and connected to said accumulating means,

1. said accumulating means triggering said switching means to actuate the device after a number of said periodic pulses have been accumulated.

4. The system defined in claim 3, wherein said detector comprises a super-regenerative detector.