US2197028A - Protective device - Google Patents

Description

Patenfie A 11% E, EG

ummo 'STATES PROTEC'IIVE DEVICE Irving Wolfl, Merchantvllle, N. J., assignor to Radio Corporatlon of Amerlca, a corporation 01' Delaware Appllcation October 28, 1936, Serial N0. 107,965

11 Claims.

My invention relates to protectlve devices and more particularly to a radio system which provides means for creating standing waves in an enclosed region to be protec ted and indicating any change in said standing waves.

I am aware that rooms have been protected by a radio transmltter whlch is arranged to radiate waves to a receiver which indicates changes caused by interception of the waves. While such devices provide some protection under Suitable conditions, I have found that the sensitivity of radio room protective devices can be greatly improved by means of the novel arrangements hereinafter described.

5 One of the objects of my invention is to provide an improved apparatus and method of operation for protecting an enclosed region by creating radio waves which have a standing wave pattern and indicating changes in said pattern.

20 Another object is to provide means for creating standing waves from a radio transmitter which is indirectly located with respect to a receiver whereby direct radiation from transmltter to re ceiver is prevented, and the standing wave pat- 25 tern is spread throughout the region to be protected.

A further object is to provide means for creating standing waves from a radlo transmitter which are received by a balanced receiving device 30 whereby a slight change in the standing wave pattern may be indicated.

An additional object is to provide means for creating stan waves from a radio transmitter which are received by a receiver and 130 impress on said receiver waves opposing the received radiated waves by means of an appropriate transmission line coupling the transmitter and the receiver.

My invention is illustrated by the accompany- 40 ing drawings in which Fig. 1 is a schematic illustration of one embodiment of my invention,

Fig. 2 is a schematic illustration of modification of my invention in which a balanced recelver is used,

Fig. 3 is a schematlc illustration of a receiver which is operated as a balanced device by impressing thereon oppositely phased currents transmitted from transmltter to receiver by a transmission line,

50 Fig. 4 is a circuit diagram of a transmitter which is indicated schematically in Figs. 1, 2 and 3, and

Fig. 5 is a circuit diagram of a receiver which is indicated schematically in Figs. 1, 2 and 3.

55 In describing the foregoing figures similar (GI. 177-314) s reference numerals will be used to lndlcate simllar parts. Referring to Fig. 1, an enclosed region I to be protected may be a room, tactory; warehouse or the like. Within the room there may be located storage bins 3, machinery, boxes 5 or goods. In one corner of the region 1s located an ultra high frequency tra.nsmitter 5 which radiates waves. These waves are reflected throughout the region and follow devlous paths to a receiver 2 which is so located that lt 10 is not: subject to direct radiatlon from the' transmitter 5. The objects in the room may be used as a shield or a shield 6 may be provlded. One

or more wave refiectors 9 may be used in certain installations to insure reflection of the waves to and throughout relatively narrow isles II. The output of the receiver is impressed on a suitable alarm i3.

The operation of the system is as follows: The transmitter, which will be more ful1y described below, radiates modulated ultra high frequency waves. These waves, preferably of a wave length of lass than one meter, are reflected from the walls, bins and objects within the region to be protected. A reflector 9 may be used to insure refiection of the waves throughout narrow isles.

The waves, after repeated reflections, are recelved at the receiver and demodulated. The received waves are made up of various components established by the standing waves throughout the region. If, after the receiver has been adjusted, a foreign body, such as a man I5, enters the region, the ultra high frequency standing wave pattern will be altered. Such alteration in the standing wave pattern will be registered in the received demodulated currents which control the alarm I3.

I prefer to employ a, relatively weak slgnal so that its effects will be prlmarily limited to the region to be protected. I have found that direct 40 radiation from the transmitter to the receiver should be avoided because it reduces the sensltivity 013 the system in parts of the room nutside the direct transmission path. The presence o1 a man may be readily detected by the change 4l which bis body causes in the standing wave pattern. The numer ous reflections from the walls, bins 3, and installed reflector 9 produce a wave pattern which will completely cover the region to be protected so that the entry of a man or movement of a sizable object anywhere within the region will alter the standing wave pattern. Best results will be obtained if the transmitter, receiver, reflector and shie1d are so located that the wave energy in diflerent parts of the region is u nearly the same. The shielding prevents direct radlation which otherwise would permlt a large amount 012 dlrect receptlon which would mask the eflects of the interceptlon of the waves in the more remote portions of the protected region. II: should be understood that at ultra high frequencies both lnsulators and conductors may be used as wave shields. The purpose of these shields is not to prevent the energy of the transmitters from reachlng the receiver laut to act as baflles which cause the transmitted wave to take a devious path to the recelver.

In Flg. 2, a pair of antennas IT, I9 are coupled to the input of the receiver 1. The coupling of one I! of these antennas is adjustable by a knob or other suitable means 2I. An adjustable reflector 23, which is mechanically connected to a control means 25, m'ay be'used in conjunction with the adjustable antenna coupling 130 eflect a balancing of the waves received by the two antennas. The antenna coupling control means 2I and the refiector control means 25 are preferably located outside the region to be protected so that the normal balance will not be afl'ected by the presence-of I;he person making the adjustments within the protected reglon I.

The output of the balanced receiving system is connected to a suitable alarm I3. The operation of the balanced system is essentially the same as the preceding system, but the sensitlvity of the balanced system is superlor. The balanced recelver is easily unbalanced by a relatively slight change in the'wave pattern. Such changes may be caused by the entry of a. man, the entry of an object, or the movement of objects within the protected region.

.Fig. 3 represents a modification 015 Fig. 2 in that a transmlsslon line 21 is usecl to convey balancing currents from the transmitter to the receiver. The transmission line is coupled at the transmitter by a coupling coil 29 o1 the like and terminated in a variable coupling means 3I whose control knob 33 is located outside of the region I. The length of the transmission line 35 between the variable coupling 3I and the receiver I may be adjustecl by trombones 31 counected to outside control handles 39.

The transmission lines are preferably terminated in their surge impedance so that variationsof length do noI: change the energy transfer.

II: is necessary that the amplitude cf the received radiated wave and the wave transferred over the line 21 be adjusted to have equal and opposite elfects on the recelver. This condition may be realized by disconnecting the transmission line 35, and observing the output currents of the receiver when the antenna II is connected and the transmitter and receiver are adjusted to obtain the required frequency and resonant conditions. The receiving antenna 4I may then be disconnected and the transmission line 35 connected to the receiver. The output currents are adjusted by varying the transmission line coupling 3I until the output currents equal the value previously obtained for the received radiated wave. The antenna II and the transmlssion line 35 are then both connected to the receiver 5 and the phase of the current transferred by the transmission line 35 adjusted by varying the trombones 31 until the phases are opposite. Thus the two currents are made equal and opposite to balance I;he receiver output.

The balanced type cf receiving system is not only more sensitive but also less subject to fluctuatlon in the output currents. The recelver may vary withln rather wide llmits wlthout upsei:tlng the balance between the two antenas or antenna. and transmission line currents. Likewlse, the amplitude of the radiated waves may vary without upsetting the balanced condition. I have found it most; desirable to maintain constant frequency at the transmitter to avoid fluctuatlons of the standing wave patterns.

In Flg. 4 a schematic circult diagram indicates one sultable form of transm-itter illustrated in the preceding figures by reference numeral 5. A crystal, er other constant frequency oscillator 43 is coupled to one or more frequency doublers 45 and an amplifier H. The modulating current source 49 is connected to the amplifier H. The output of the amplifier 41 is coupled to a dipole er like antenna 5I. II: should be understood that a modulated oscillator without frequeney doublers and amplifiers may be used.

A receiving apparatus, previously represented by the reference numeral I is shown schematically by the circuit diagram of Fig. 5. An antenna 53 is coupled to a tunable circuit 55 and a rectifier 51. The rectified currents are impressed across the resistor 59 which is coupled to the input; of a signal frequency amplifier GI. The output cf the signal frequency amplifier GI may be coupled to a second amplifier 63. An alternating current relay 65 is connected in the output of the second arnplifier to oberate the signal alarm I3 which may be located at a point remote from the protected region. A D. C. relay 61 is connected in series wlth the amplifier anode current supply 69 to operate an indicator II which shows any disconnection or failure of the battery G9. This indicator may be placed near the alarm I3. The alarm I3 is connected so that failure o1 the recelver or the transmitter, as well as a variatlon of the received signals, will operate the alarm. It; should be understood that the alarm may be counected so as to only operate on the interception of the waves, and another indlcator may be used to represent defectzs in the service.

Thus I have describecl a protective device which may be installed withln a warehouse room, or other enclosed space. An ultra high frequency Isransmitter radlates waves which reach the receiver a1'ter repeated reflections. These refiections create standing waves which glve a normal sigma] indication or a balanced receiver output. A variation cf the standing waves, created by the entrance of a man, or movement cf objects within the room, changes the receiver output and. operates an alarm slgnal. II; should be understood that the wave may be modulated or unmodulated and that two or more transmitters and two or more receivers may be used as may be required in any particular installation.

I claim as my invention:

1. The method of protecting an enclosed region by means including a radio transmitter and a radio receiver which comprises radiating an ultra. high frequency radio wave, limiting direct radiation from said transmitter to said receiver, creat- Ing standing waves by reflecting said waves within said region, independently receiving componerzts of said reflected waves substantially equal in amplitude and opposite in phase, adding said components, and indicating changes in pattern of said standing waves by their effect on said addition.

2. The method of protecting an enclosed region by means including a radio transmitter and a radio receiver which comprises radiating an ultra high frequency radio wave, preventing sald radiation from directly reaching' said receiver, creating standing waves by reflecting said radiated waves, independently receiving two out of phase components of said reflected waves, balancing said components against each other, and indicating a. change in said balancte caused by a change in the phase of said received waves effected by a body moving within said region.

3. The method of protecting an enclosed region E:vy means including a radio transmitter and a radio receiver which comprises radiating an u1tra high frequency modulated radio wave, preventing said radiation from direct1y reaching said recelver, creating standing waves by refiecting seid radiated waves, independently receiving two out of phase components of said reflected waves, balancing said components against each other, and indicating a change in said balance caused by a. change in the phase relation of said received waves effected by a body moving within said region.

4. The method of protecting an enclosed region by means of a radio transmitter and receiver which comprises radiating a radio waire, limiting the direct radiation from sald transmitter to said receiver, creating standing waves by reflecting said waves within said region, independently receiving two out of phase components of said reflected waves, shielding said receiver from direct radiation from said transmitter, and indicating changes in the phase relation of said received waves caused by the movement of a body within said enclosed region.

5. The method of protecting an enclosed region Which comprises radiating a radio wave within said reglon, establishing standing waves by refiecting said waves within said region, receiving said reflected waves, combining therewith an opposing out of phase wave free from reflections 130 balance said recelved refiected wave, and indicating a change in said balance caused by a change in the phase of said received reflected waves.

6. The method of protecting an enclosed region which comprises radiating a radio wave within said reglonestablishing standing waves by refiecting said waves within said region, receiving said reflected waves, combining therewith an opposing out of phase wave free from refiections to balance said received reflected wave, adjusting the amplitude and phase cf said opposing wave, and indicating a change in said balance caused by a change in phase of seid received reflected waves.

7 In a system for protecting an enclosed region a transmitter of ultra high frequency waves, a receiver having two antennas responsive to said waves, means for impressing components of said waves of opposite phase on said antennas, means for equalizing the amplitudes of said components of opposite phase, means for reflecting said waves to create standing waves throughout said region, and means for indicating a change in the phase of said standing waves ca'used by the movement of a body within said region.

8. In a system for protebting an enclosed region a transmitter for radiating ultra high frequency waves within said region, a receiver responsive to said waves, means.for reflecting said waves to create standing waves throughout said region, a transmission 1ine coupling said receiver and transmitter for impressing out of phase balancing waves on said receiver, and means for indicating a. change in said balancing caused by the movement of a body Within said region.

9. In a system of the character cf claim 8 means for adjusting the amplitude and phase of said balancing waves.

10. The method o1 protecting an enclosed region by means including a radio transmitter and a radio receiver which comprises radiating an ultra high frequency radio wave within said enclosed region, creating standing waves by reflecting said waves within said region, independently impressing on said receiver two radio frequency voltages, at least one of which is derlved from said standing waves, balancing said voltages and indicating changes in the pattern of said standing waves as a function of changes in said balance.

11. The method of protecting an enclosed region by means including a, radio transmitter and a radio receiver which comprises radiating an ultra high frequency radio wave within said enclosed region, creatlng standing waves by reflecting said waves within said region, independently impressing on said receiver two radio frequency voltages having instantaneously equa1 amplitudes and opposite polarities, the relative instantaneous amplitude of a1: least one of said voltages being a function of said standing wave pattern, adding said voltages, and indicating changes in the instantaneous amplitude of sa1d one voltage due to changes in said standing wave pattern.

IRVING WOL'E'F.

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