U.S. patent number 3,696,368 [Application Number 04/816,320] was granted by the patent office on 1972-10-03 for radio frequency burglar alarm system.
Invention is credited to Ray B. Kauffman.
United States Patent |
3,696,368 |
Kauffman |
October 3, 1972 |
RADIO FREQUENCY BURGLAR ALARM SYSTEM
Abstract
The burglar alarm system utilizes a transmitter that transmits
an RF signal which is both amplitude modulated and frequency
modulated. The signal is received by a receiver which is capable of
sensing increases or decreases in the received energy due to
movement through or into the energy field which is generated and
radiated by the transmitter. This change in energy level causes the
receiver to trigger an alarm.
Inventors: |
Kauffman; Ray B. (Seabrook,
MD) |
Family
ID: |
25220269 |
Appl.
No.: |
04/816,320 |
Filed: |
April 15, 1969 |
Current U.S.
Class: |
340/553;
455/41.1 |
Current CPC
Class: |
G01V
3/12 (20130101) |
Current International
Class: |
G01V
3/12 (20060101); G08b 013/00 () |
Field of
Search: |
;340/258A,258B
;325/29,131 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Caldwell; John W.
Assistant Examiner: Slobasky; Michael
Claims
What is claimed is:
1. An intrusion detection system for detecting the intrusion of a
moving object, comprising:
means for generating a frequency modulated signal of a first
frequency band which continuously sweeps from a first to a second
frequency having its amplitude modulated by a second frequency,
means for radiating said frequency modulated and amplitude
modulated signal connected to said generating means, and
means for receiving said frequency modulated and amplitude
modulated signal containing means for detecting amplitude changes
in said received frequency modulated and amplitude modulated
signal, said signal amplitude changes at the receiving means
indicating the intrusion of a foreign object, said means for
generating a frequency modulated signal having its amplitude
modulated by a second frequency comprising an oscillator including
an electronic valve whose bias is gradually being built up to cause
said electronic valve to cut off whereby the building up of said
bias causing said electronic valve to become less conductive
thereby amplitude modulating the frequency modulated signal.
2. An intrusion detection system as defined in claim 1, but further
characterized by said receiver means having means for automatically
controlling the level of received frequency modulated signal so
that the relative position of said radiating means and said
receiving means does not affect the operation of said receiver.
3. An intrusion detection system as defined in claim 2, but further
characterized by having means responsive to said means for
detecting amplitude changes for triggering an alarm indicating
means.
4. An intrusion detection system having a receiver for detecting
directly radiated frequency modulated and amplitude modulated radio
frequency wave from a transmitting antenna and a radio frequency
wave which is reflected from an intruder, the intruder affecting
the amplitude of the received signal, comprising:
a transmitter means for generating said frequency modulated and
amplitude modulated wave comprising an oscillator including an
electronic valve whose bias is gradually being built up to cause
said electronic valve to cut off whereby the building up of said
bias causes said electronic valve to become less conductive thereby
amplitude modulating the frequency modulated signal,
means for receiving said frequency modulated and amplitude
modulated radio frequency wave energy,
means for detecting said radio frequency modulated wave connected
to said receiving means,
means for amplifying said detected frequency modulated signal
connected to said detecting means, said amplifier means having an
output,
means for detecting both positive and negative changes in amplitude
of said frequency modulated detected signal on said output of said
amplifier means, and
detector means responsive to said both positive and negative
detected amplitude changes of said frequency modulated detected
signal for triggering an alarm means whereby both positive and
negative changes in said detected signal cause said alarm to be
triggered.
5. An intrusion detection system as defined in claim 4, but further
characterized by having an automatic level control means for
controlling the level of the detected signal connected to said
means for detecting said radio frequency wave energy.
6. An intrusion detecting system as defined in claim 1, but further
characterized by said receiving means having an antenna, a tuned
circuit means tuned to said frequency modulated signal having an
input and an output, said means for detecting amplitude changes
having an input and an output, said antenna connected to said tuned
circuit input, said output of said tuned circuit connected to said
input of said means for detecting amplitude changes, and an
amplifier means having a tuned bandpass filter, said amplifier
means having an input and an output, said amplifier input being
connected to said output of said means for detecting amplitude
changes and said amplifier output having a signal which is
indicative of the amplitude of the received frequency modulated
signal.
7. An intrusion detecting system as defined in claim 6, but further
characterized by said receiving means having a second detector
having an input and an output, a second amplifier having an input
and an output, said second detector input connected to said output
of said amplifier having a bandpass filter, said output of said
second detector being connected to said input of said second
amplifier,
an automatic level control means having an input and an output,
said automatic level control means input connected to said output
of said second amplifier and said output of said automatic level
control connected to said means for detecting amplitude changes in
said frequency modulated signal,
means for detecting positive and negative changes of signal level
having an input and an output, said input of said means for
detecting positive and negative changes being connected to said
output of said second amplifier, and
an alarm indicating means having an input connected to said output
of said means for detecting positive and negative changes in said
signal level whereby changes in said signal level trigger an alarm
indicating the presence of an intruder.
8. An intrusion detection system having a zone of protection about
a periphery, comprising:
means for generating a radio frequency signal which continuously
sweeps from a first frequency to a second frequency,
means for radiating said radio frequency signal connected to said
radio frequency generating means,
means for receiving said radio frequency signal from said radiating
means and reflections of said radio frequency signals from an
object entering the electro-magnetic field caused by said radiated
radio frequency signal,
means for mixing said received radio frequency signal received from
said radiating means with said radio frequency signal reflected
from said intruded object generating a beat signal connected to
said receiving means,
means for passing said generated beat signal of a predetermined
frequency bandwidth connected to said mixing means,
said means for passing said generated beat signal determining the
periphery of the zone of protection,
means for detecting amplitude changes of said band passed beat
frequency connected to said band passing means, and
means for generating an alarm responsive to said amplitude changes
detected by said change detected means connected to said change
detecting means whereby amplitude changes in said band passed
signal is indicative of an intruding object entering said protected
perimeter of said radio frequency radiation field,
whereby an intruder in said zone of protection about said periphery
causes said alarm to be sounded.
9. An intrusion detection system having a zone of protection about
a periphery defined in claim 8, but further characterized by said
means for generating continuously varying radio frequency signal,
is provided with means for varying the rate of the frequency sweep
whereby said periphery of said zone of protection is changed when
said frequency sweep rate is changed.
10. An intrusion detecting system as defined in claim 2, but
further characterized by said receiving means having an antenna, a
tuned circuit means tuned to said frequency modulated signal having
an input and an output, said means for detecting amplitude changes
having an input and an output, said antenna connected to said tuned
circuit input, said output of said tuned circuit connected to said
input of said means for detecting amplitude changes, and an
amplifier means having a tuned bandpass filter, said amplifier
means having an input and an output, said amplifier input being
connected to said output of said means for detecting amplitude
changes and said amplifier output having a signal which is
indicative of the amplitude of the received frequency modulated
signal.
11. An intrusion detection system as defined in claim 1, but
further characterized by said means for generating a frequency
modulated signal comprising:
an electronic valve having means connected thereto to cause said
valve to oscillate,
means causing the frequency of said oscillating valve to change
connected to said oscillating electronic valve, and
means for changing the rate of frequency change of said oscillating
electronic valve connected to said frequency changing means.
12. An intrusion detection system as defined in claim 11, but
further defined by said means for causing said oscillating
frequency to change comprising a variable capacitance diode and
said means for changing rate frequency changes comprising a
sawtooth wave generator.
Description
The invention relates to a burglar alarm for protecting a given
area and more particularly, to a burglar alarm system which
radiates a field of RF energy over the area to be protected and a
receiver for monitoring the RF energy in the protected area.
For example, the desireability of protecting a given space by an
electronic device has been established. Very briefly, the automatic
protection of a given space by an electronic monitoring system of
moderate cost can be a help to the law enforcement divisions of the
cities and states. Burglar alarms of various types have been used
in the prior art. However, the prior art RF burglar alarm system
can be triggered by stray radiations from other electronic devices,
are relatively complex and are costly to purchase.
An object of the invention is to provide an RF burglar alarm system
which is insensitive to electrical disturbances caused by radios,
the operation of electronic equipment and by the movement of motor
vehicles and airplanes in the proximity of the area which is to be
protected.
A further object of the invention is to provide a simple RF burglar
alarm system for protecting a given area.
Another object of the invention is to provide a simple electronic
burglar alarm system for protecting the perimeter of an area to be
protected.
A still further object of the invention is to provide an RF burglar
alarm which utilizes a pulse and frequency modulated carrier wave
as the protective medium.
A still another object of the invention is to provide a burglar
alarm system having an automatic level control thereby permitting
the transmitter and receiver to be placed at varying distances from
each other.
In accordance with the preferred form of the invention, a
transmitter is provided with an oscillator which produces a
frequency modulated signal which sweeps a preselected frequency
band. This frequency modulated signal is also amplitude modulated.
The receiver is tuned to receive the frequency band of the
transmitter. Objects entering or leaving the radiated field of the
transmitter change the amount of energy received at the receiver.
The change in the received energy actuates an alarm.
In a second embodiment of the invention the transmitter produces a
frequency modulated signal which sweeps through a band from a first
frequency to a second. The receiver receives both the direct
radiation of the transmitter and the reflected wave from the
intruder. The received waves will generate a beat note difference
signal. Only the received waves which generated a beat signal in a
precise range corresponding to a given perimeter which encloses the
transmitter and the receiver will be permitted to get through the
receiver bandwidth filter to trigger the alarm.
Other objects and many of the intended advantages of this invention
will be readily appreciated as the same becomes better understood
by reference to the following detailed description when considered
in connection with the accompanying drawings, wherein:
FIG. 1 is a block diagram illustrating the broad principles of an
RF burglar alarm system;
FIG. 2 is a schematic circuit diagram of a suitable transmitter
unit for use in a burglar alarm system constructed in accordance
with the present invention;
FIG. 3 is a schematic block diagram of a suitable receiver
constructed in accordance with the present invention;
FIG. 4 is a circuit diagram of the receiver illustrated in block
diagram form in FIG. 3; and
FIG. 5 is an alternate circuit diagram for a suitable
transmitter.
Referring to FIG. 1. There is illustrated a transmitter 11
connected to an antenna 13 for radiating an RF energy field about
the transmitter. At a suitable distance from the transmitter 11 is
located a receiver 17 having an antenna 19. The antenna 19 detects
the energy radiated from the antenna 13. The receiver 17 monitors
the detected energy from the antenna 19 and if a sudden change in
the energy level should occur, either upwards or downwards, then
the alarm 21 is triggered. A change in energy occurs when a foreign
object moves into the RF field radiated from the antenna 13 and
detected by the antenna 19.
Referring to FIG. 2. There is illustrated a suitable oscillator for
generating the RF energy for use in transmitter 11. The oscillator
is provided with an NPN transistor 61 having an emitter electrode
62, a base electrode 63 and a collector electrode 64. It is to be
understood throughout this disclosure that NPN transistors can have
PNP transistors substituted therefor with the simple expedience of
changing the bias polarity and that PNP transistors may also have
NPN transferred for them by the same expediency. For the transistor
in this embodiment, a 9-volt battery 85 is connected through a
resistor 77 to the base 63 of the transistor 61. A second resistor
81 is connected between the base electrode 63 of the transistor 61
and ground. A by-pass capacitor 79 is connected across the resistor
81 and a low impedance by-pass capacitor 83 is connected across the
battery 85.
The oscillator has an inductor coil 75 connected between the
positive terminal of the battery 85 and the collector electrode 64
of the transistor 61. A feedback capacitor 67 is connected between
the collector electrode 64 of the transistor 61 and the emitter
electrode 62 of the transistor 61. The combination of the inductor
75 and the capacitor 67 determines the resonant frequency of the
pulses generated by the oscillator. This resonant frequency for a
suitable laboratory embodiment was approximately 280 megaHertz. An
inductor 69 has one of its ends connected to the emitter electrode
62 of the transistor 61 and its other end connected to one end of a
resistor 71. The other end of resistor 71 is connected to ground.
The resistor 71 has a capacitor 73 connected in parallel
therewith.
The operation of the oscillator illustrated in FIG. 2 is as
follows. As soon as the battery 85 is connected into the circuit, a
voltage is developed on the base 63 of the transistor 61 and on the
collector 64 of the transistor 61 such that it begins to conduct
and oscillate. The oscillations of the transistor 61 are in the
order of 280 megaHertz at the beginning of the oscillatory circuit
cycle. The current flowing through the transistor 61 is fed back in
phase by the capacitor 67 from the collector electrode 64 of the
transistor 61 to the emitter electrode 62 of the transistor 61. The
DC bias on the emitter electrode 62 is gradually being built up
during the oscillatory cycle to a point wherein the emitter is
biased more positive than the base electrode 63 of the transistor
61. When this occurs, the transmitter is cut off. As the capacitor
73 charges up making the emitter 62 of the transistor 61 more
positive, the frequency of the oscillator drifts, sweeps downward
from 280 megaHertz to 270 megaHertz. The net effect of the
operation is thus: there is an oscillating frequency swept from 280
megaHertz to 270 megaHertz in bursts of 10 kiloHertz each. That is
to say the time constant between bursts of oscillatory energy is
determined by the resistor 71 and the capacitor 73. When the
resistor 71 discharges the capacitor 73 to a sufficient amount then
the emitter electrode 62 will then be biased to a low enough
voltage to permit the transistor 61 to become conductive again and
to begin the cycle all over. The positive DC bias on the emitter
electrode controls the conductivity of the transistor 61. As the DC
bias builds up it reduces the conductivity of the transistor
thereby amplitude modulating the frequency modulated wave of the
oscillator. The output of the oscillator is a series of pulses,
each pulse containing a sweep frequency from 280 megaHertz down to
270 megaHertz, each pulse having a width of approximately 1
microsecond, and the pulses are spaced apart approximately 100
microseconds in the laboratory embodiment built by the
inventor.
Referring to FIG. 3. There is illustrated a block diagram of a
receiver which is utilized in the preferred embodiment of the
invention. The circuitry of the receiver is illustrated in FIG. 4
and will be discussed hereinafter. The antenna 19 of the receiver
has its output connected to an input of the detector 25. The
detector 25 is connected through a suitable channel 26 to the
amplifier 27. The output of the amplifier 27 is connected through a
suitable channel 28 to a second detector 29, and the output of the
second detector is fed through to a second amplifier 31. The output
from the amplifier 31 is fed through a channel 33 to the input of a
low frequency amplifier 39 and simultaneously through a second
channel 34 to an automatic level control 35. The output of the
automatic level control is fed to a level adjusting input of the
detector 25. The output of the low frequency amplifier 39 is fed to
a third detector 43 and is then fed to a threshold detector 45. The
output of the threshold detector 45 is fed to a relay driver 49
which drives a relay alarm 53.
The operation of the receiver is as follows. The RF field from the
transmitter antenna 13 is picked up by the antenna 19 of the
receiver. The detector 25 converts this RF energy into a series of
DC pulses which are amplified by the amplifier 27 and the amplified
pulse train is then further detected by detector 29. The output of
detector 29 is further amplified by the amplifier 31. Part of the
amplified energy of the amplifier 31 is fed back through an
automatic level control 35 to a level control input of the detector
25. This feedback controls the sensitivity of the detector 25.
Therefore, if the transmitter is very close to the antenna,
amplifier 27 will not be overloaded because the feedback from the
amplifier 31 through the automatic level control 35 to the detector
25 will reduce the sensitivity of the detector 25 and hence the
size of the pulse entering amplifier 27.
The remaining output of the amplifier 31 is fed to a low frequency
amplifier 39. The output of the low frequency amplifier 39 is a
variable DC voltage which varies when someone walks within the
field range of the RF energy of the transmitter antenna 13. The
variations in the output of the low frequency amplifier is detected
by detector 43. Specifically, the detector 43 detects either an
increase or a decrease in the level of the voltage from the output
of the low frequency amplifier 39. The threshold detector 45
determines how much this voltage must deviate before it is passed
on to a relay driver 49 which in turn trips the relay 53.
Referring to FIG. 4, wherein the detailed circuitry of the block
diagram of FIG. 3 is illustrated. The antenna 19 is connected to
the junction of a capacitor 101 and an inductor 103 of the
receiver. The capacitor 101 and inductor 103 are tuned to a value
to permit the FM bandpass of 270 to 280 megaHertz to be received by
the FM receiver. The other end of capacitor 101 is connected to
ground and the other end of the inductor 103 is connected to
ground. A capacitor 105 is connected between a center tap on the
inductor 103 and the anode of the diode 107.
A resistive divider of resistors 111 and 109 are connected in
series between ground and one side of resistor 251. The resistors
111 and 109 set the bias on the cathode of the diode 107. A
capacitor 113 has one of its ends connected to the cathode of diode
107 and its other end connected to the base electrode 123 of the
transistor 121. A diode 118 has its cathode connected to the base
electrode 123 of the transistor 121 and its anode of diode 118 is
connected to ground. A filtering capacitor 117 is connected between
one end of the resistor 251 and ground to filter out any AC
voltages on the B+ supply line. The Zener diode 253 is connected
between the same terminal as the capacitor and ground and prevents
positive excursions from shorting out or burning out the
transistors of the circuit. Additionally, the Zener diode prevents
false activation of the alarm due to power supply changes and/or
transients. A feedback resistor 115 is connected between the
emitter of transistor 141 and the base electrode 123 of the
transistor 121.
The transistor 121 is an emitter follower transistor and has a
resistor 125 connected between the emitter electrode 122 of the
transistor 121 and ground. The base electrode of the transistor 131
is connected directly to the emitter electrode 122 of the
transistor 121 and the collector electrode 124 of the transistor
121 is connected between the junction of the resistors 129 and 127.
The resistors 129 and 127 are connected in series between a
terminal of the resistor 251 and the collector of the transistor
131. The emitter of transistor 131 is directly connected to ground.
The collector of transistor 131 is directly connected to the base
electrode of the transistor 141. A resistor is connected between
the emitter electrode of the transistor 141 and ground. The output
of the amplifiers 121, 131 and 141 is directly connected to P3.
Between P3 and P4 is connected a high pass filter comprising a
capacitor 145 and resistor 147 and a low pass filter which
comprises a capacitor 149 is connected between P4 and ground. The
center point of the filter is 10 kiloHertz and the 3db points are
at 7 kiloHertz and 13 kiloHertz. The output of the filter at P4 is
directly connected to the base electrode of transistor 153. The DC
bias level on the base of transistor 153 is set by the series
resistors 201, 203 and 205. The emitter of the transistor 153 is
directly connected to ground. The collector of the transistor 153
is connected through a resistor 155 to the junction point of the
cathode of the Zener diode 253 and the resistor 251. The output of
the collector electrode of transistor 153 is directly connected to
the base electrode of the transistor 165. A resistor 167 is
connected between the junction of the cathode of Zener diode 253
and the resistor 251 and the collector electrode of the transistor
165. The emitter electrode of the transistor 165 is connected
through a resistor 171 to ground. The emitter electrode of
transistor 165 is connected to P5 as an output of the amplifier
stage.
At this point it may be well worthwhile to state that the diode 107
is the detector 25 and the amplifier 27 comprises the transistors
121, 131, 141, 153 and 165.
The voltage at terminal P5 is coupled by a capacitor 173 to the
terminal P6. The diode 175 has its cathode connected to the P6
terminal and its anode connected to ground. The diode 175 is the
detector 29 of the block diagram of FIG. 3. The amplifier 31 of
FIG. 3 is the transistor 181.
The transistor 181 has an emitter electrode 182 which is directly
connected to ground. A base electrode 183 which is connected to P6
and a collector electrode 184 which is connected to P7. The
resistor 225 has one of its ends connected to the collector
electrode 184 of the transistor 181 and its other end connected to
the line 256 which is to be connected to the source of B+
potential. The other end of resistor 251 is connected to the line
256. The transistors 227 and 237 perform the function of a voltage
regulator and set the amplifying level of the transistor 181. This
is accomplished by setting the bias level on the base of electrode
183 of the transistor 181 through adjusting the potential across
the resistor 238. The transistors 207 and 217 perform the function
of a voltage regulator and set the amplification level of
transistor 153. The output of the amplifier 184 is connected to P7
which in turn is connected to one end of the capacitor 185. The
other end of the capacitor 185 is connected to ground. The
capacitor 185 is a filter capacitor.
The resistor 189 has one of its ends connected to the capacitor 185
and has its other end connected to one terminal of a capacitor 191.
The other terminal of capacitor 191 is connected to ground. The
capacitor 191 is a second filter capacitor. The capacitor 191,
resistor 189 and capacitor 185 perform the function of the
automatic level control element 35 of FIG. 3. The capacitor 191 is
connected to the anode of the diode 107 by way of a resistor
193.
The output of P7 is coupled to a capacitor 259 and a resistor 261
to the base electrode 269 of the transistor 267. The transistor 267
and the transistor 271 perform the function of the low frequency
amplifier 39 of FIG. 3. The transistor 267 has an emitter electrode
268, a base electrode 269 and a collector electrode 270. A
capacitor 265 is connected between the base electrode 269 of the
transistor 267 and ground. The emitter electrode 268 of the
transistor 267 is connected to the emitter electrode 272 of the
transistor 271. The emitter electrodes 268 and 272 of the
respective transistors 267 and 271 are connected through a variable
resistor 275 to ground. The transistors 267 and 271 are a
differential amplifier.
The collector electrode 270 of the transistor 267 is connected
through a resistor 279 to the common B+ voltage line 256.
Similarly, the collector electrode 274 is connected through the
resistor 281 to the common B+ line 256. The base electrode 273 of
the transistor 271 is connected to the anode of diode 277. The
cathode of diode 277 is connected directly to ground. Diode 277
performs the function of a temperature stabilizing reference for
transistor 271. A resistor 263 is connected between the base
electrode 273 of the transistor 271 and the base electrode 269 of
the transistor 267. A resistor 283 is connected between the B+
common line 256 and the base electrode 273 of the transistor
271.
Diodes 287 and 285 perform the function of the detector 43 of FIG.
3. The cathode of diode 285 is connected to the collector electrode
270 of the transistor 267 and the anode of the diode 285 is
connected to the base electrode 293 of the transistor 291.
Similarly, the cathode of the diode 287 is directly connected to
the collector electrode 274 of the transistor 273 and the anode of
the diode 287 is directly connected to the base electrode 293 of
the transistor 291. A resistor 289 is connected between the common
B+ line 256 and the base electrode 293 of the transistor 291. The
emitter electrode 292 of the transistor 291 is directly connected
to the common B+ line 256. A filter capacitor 295 is connected
between the collector electrode 294 of the transistor 291 and
ground. A resistor 297 is connected between the collector electrode
294 of transistor 291 and ground. A capacitor 299 is connected in
parallel with the resistor 297.
The transistor 303 performs the function of the relay driver 49 of
the block diagram of FIG. 3. The transistor 303 has an emitter
electrode 304, a base electrode 305 and a collector electrode 307.
The base electrode 305 of the transistor 303 is connected through a
resistor 301 to the collector electrode 294 of the transistor 291.
The collector electrode 307 of the transistor 303 is connected to
one end of a relay 309 which operates the switch contacts 317, 315
and 314. The other end of the relay 309 is connected to the common
B+ voltage line 256. An output is provided and is taken from the
base electrode 305 of the transistor 303 and connected to the
output terminal 321 which in this embodiment is not connected to
anything and which may be used to remotely disable or enable the
alarm or to send a signal to a fire station, a police station, or
other place where a central monitoring board may be located.
The threshold detector 45 of the block diagram of FIG. 3 is the
transistor 323, variable resistor 331 and resistor 329. The
transistor 323 has an emitter electrode 325, a base electrode 326
and a collector electrode 327. The base electrode 326 of the
transistor 323 is connected through the series combination of the
variable resistor 331 and a fixed resistor 329 to the source of B+
potential line 256. A resistor 333 is connected between ground and
the base electrode 326 of the transistor 323. The collector
electrode 327 of the transistor 323 is directly connected to
ground. The emitter electrode 325 of the transistor 323 is directly
connected to the emitter electrode 304 of the transistor 303.
The RF radiated energy which is picked up by antenna 19 is fed
through the tuned circuit of capacitor 101 and inductor 103 at the
280 to 270 megaHertz bandwidth. The detector which comprises a
diode 107 detects a series of pulses at about the 10 kiloHertz
frequency which is the pulsed frequency of the oscillator in the
transmitter. The diode 107 is an AM detector which detects the
amplitude of the overall FM signal to which the antenna is tuned.
This amplitude varies at a 10 kiloHertz rate. The 10 kiloHertz
pulses are coupled by the capacitor 113 to the amplifier
transistors 121, 131 and 141 of the first stage of amplification of
the amplifier 27. The output of the first stage is fed through a
high pass filter which comprises the capacitor 145 and resistor 147
which passes all frequencies above 7 kiloHertz the sdb point to P4.
The capacitor 149 is so chosen that its 3db point is 13 kiloHertz
and therefore shorts to ground or frequencies above 13 kiloHertz
and passes through to P4 all frequencies below 13 kiloHertz. The
second stage of amplification of the amplifier 27 is accomplished
by the transistors 153 and 165. Therefore, the output frequency at
P5 ranges from 7 kiloHertz to 13 kiloHertz.
The detector 29 (diode 175) shorts the negative going pulses to
ground and provides a positive potential to P6 which is the
amplifier 31 (transistor 181). The transistor 181 amplifies the
signal presented to its base electrode 183 and provides an output
at terminal P7. Part of this output is filtered through the
combination of capacitor 185, resistor 189 and capacitor 191 and is
used as an automatic level control feedback shown schematically in
box 35. The output of the amplifier 184 is a steady state DC level
determined by the power of the transmitted field so that if the
transmitted field becomes higher, part of the signal which is fed
back in the automatic level control is returned through the
resistors 189 and 193 to the anode of diode 107. The network
comprising the capacitor 191, one resistor 189 and capacitor 185
has a very long time constant so that the operation of the diode as
regards transients or changes in the RF field is not effected. What
this network does, is establishes the DC level at which the diode
107 operates. The cathode of diode 107 is at an elevated positive
potential and will be reversed biased if the voltage across
capacitor 191 is low. This happens when the transmitting antenna 13
is very close to the receiving antenna 19 and there is a very
strong RF field on the receiving antenna 19. This establishes the
condition that the transmitter RF field will never be so strong as
to overload the amplifier section of the receiver. This makes it
impossible to jam the receiver. Now, for example, as the
transmitter and receiver antenni are moved further and further
apart, the incoming received signal of the receiver antenna 19 is
of lower absolute strength, thereby causing less feedback to
compensate for that, and in that case, the voltage across capacitor
193 will go in a more positive direction tending to almost forward
bias the diode 107 which, in fact, makes the diode 107 a very
sensitive detector. The overall combined effect of this action is
such that the output at the junction of the resistors 111 and 109
is the same level regardless of the spacing of the receiver antenna
19 from the transmitting antenna 13. The resistor 255 acts as a
load resistor for the transistor 181.
In the case where we have a steady state and there is no intruder,
capacitor 259 blocks any input to the base electrode 269 of the
transistor 267 or to the base electrode 273 of the transistor 271.
The transistors 271 and 267 are connected so as to be a
differential amplifier and as long as the DC level at P7, the
output of transistor 181 does not change, this amplifier will have
no output and hence the rest of the circuit will remain stable and
the alarm will not be triggered.
In the steady state condition the voltage drop across resistor 279
and resistor 281 is very small, in the order of a few tenths of a
volt, and not enough to cause the diodes 285 and 287 to conduct.
Therefore, transistor 291 does not conduct. Transistor 291 is
connected to transistor 303 which is the relay driver. When
transistor 291 does not conduct the transistor 303 does not conduct
and consequently the relay is not energized. Transistor 323 sets a
small threshold on transistor 303 so that random noise pulses which
tend to turn transistor 303 on, will not because of the reverse
bias at the emitter electrode of transistor 303 set by the
transistor 323.
Reverting a moment to a previous section. Transistor 207 and
transistor 217 are merely used to establish the amplification
conditions for the second two transistors 153 and 165 of the
amplifier 27. Transistors 207 and 217 control the bias condition
for the amplifier comprising the transistors 153 and 165. The
collector of transistor 217 is connected to the power supply of the
burglar alarm. The base of transistor 207 is connected to the
emitter of transistor 217 by resistor 203. As the emitter voltage
on transistor 217 tries to increase, transistor 207 will sense this
and decrease the bias voltage on the base of transistor 217. It,
transistor 207, will start to conduct, therefore holding the
emitter of transistor 217 at a voltage determined by the voltage
divider resistors 203 and 205 and base of transistor 207. This
voltage is somewhat less than 1 volt. The regulator comprising
transistors 207, 217 is connected to the base electrode of
transistor 153 establishing its bias condition at the optimum
operating point. The transistors 227 and 237 operate in the same
manner to control the bias to transistor 181, thereby maintaining
its operating point at the optimum value. A suitable circuit which
may be a single crystal may be bought on the open market and
contains the amplifier transistors 121, 131, 141, 153, 165 and the
voltage regulator 207, 217, 227 and 237 and amplifier 181 may be
numbered: CA 3035. However, it is to be understood that other
amplifiers and other voltage control regulators may be used in this
system without affecting the basic invention.
Time constants of the RC circuit resistor 255 and capacitor 259,
and resistor 261 and capacitor 265 are in the order of five seconds
so that long transients do not affect it and so that short
transients pass through the RC circuit to the base electrodes 269
and 273. However, a change in the ambient level over a period of
time, even especially a slow or slight change will not have any
effect on the detector circuit diodes 285 and 287; but any change
which is more rapid than the five second time constant triggers
transistor 267 on therefore, triggers transistor amplifier 291 and
transistor 303 and setting the alarm through the relay. A steady
state situation has now been defined.
Now, assume a man walks into the RF field having a reflective
material thereby increasing the energy received by the receiver
antenna 19. As a person enters into the field and reflects more
energy from the transmitter antenna 13 to the receiver antenna 19,
the receiving antenna 19 will suddenly pick up more energy;
therefore, the output energy of capacitor 101 and inductor 103 will
increase, the input energy to the diode detector 107 will increase
and the output energy of detector 107 will also increase.
Consequently, the output of the amplifier 27 which comprises the
two amplifier sections having transistors 121, 131, 141 and
transistors 153 and 165 will be a string of pulses having a larger
amplitude. This change happens very rapidly and as this happens at
a speed at which the person enters the field. As the output
amplitude of the pulses at P5 increases the output of the second
detector diode 175 which is called detector 29 increases. It can be
seen that the output on the detector 29 being diode 175 increases
to a higher DC positive level. This increase in voltage makes the
transistor 181 more conductive (turn on harder). When transistor
181 turns on harder, the voltage at its collector will drop
rapidly. Therefore, the rapid drop in voltage will be passed by
capacitor 259 through resistor 261 turning off the transistor 267.
When the transistor 267 turns off, its emitter current is
decreased, therefore allowing more emitter current to flow into the
emitter 272 of differential transistor 271. This turns transistor
271 on causing an increased voltage drop on resistor 281 thereby
forward biasing the diode 287 turning on the transistor 291 which
in turn, turns on the transistor 303 and keys the relay turning on
an alarm signal. The output of detector 29 and the amplifier 31 is
rapid enough so that the automatic level control feedback circuit
35 does not change substantially in order to change the conductive
level of diode 107 during this portion of the operation. The diode
277 connected to the base 273 of the transistor 271 controls the
operating point of the transistor 271. The diode 277 also has a
temperature compensation effect so that changes of temperature do
not affect the operation of this amplifier.
In the second condition, assuming that the person entering the
field absorbs some of the RF energy rather than reflecting it. In
this case, they will cause a decrease in signal strength at the
antenna 19 of the receiver. The decreased signal strength will be
fed to diode 107 and hence smaller voltage will be at the output of
the detector 25 which comprises the diode 107. Consequently, the
voltage amplitude at P5 of the integrated circuit will be less.
This will cause the detector input to transistor 181 to be less
positive in value; hence transistor 181 will draw less current and
the collector of transistor 181 will go in a more positive
direction. This positive change will be passed through the
capacitor 259 and resistor 261 and will turn on the transistor 267
increasing the voltage drop across resistor 279 and forward biasing
the diode 285, turning on transistor 291 and consequently turning
on transistor 303 thereby tripping the relay and setting off the
alarm. It is noted that this decrease that has been spoken of
heretofore is rapid enough to pass through the circuits which have
a 5 second time constant.
Referring to FIG. 5. There is disclosed an alternate oscillator
which performs the function of an alternate transmitter for use in
the disclosed invention. The resistor 401 having a variable center
tap 403 has one of its ends connected to ground and its other end
connected to the B+ voltage line 402. A resistor 405 has one of its
ends connected to the moveable center tap 403 of the resistor 401
and its other end connected to the base electrode 411 of the
transistor 409. A second resistor 407 is connected between the base
electrode 411 of the transistor 409 and the B+ line 402. The
emitter electrode 410 of the transistor 409 is connected to one end
of a resistor 415 and the other end of resistor 415 is connected to
the B+ line 402. The collector 412 of transistor 409 is connected
through the series connection of capacitor 417 and resistor 419 to
ground. A unijunction transistor 421 has its emitter electrode 423
connected to the collector electrode 412 of the transistor 409. The
first base electrode 424 of the unijunction transistor 421 is
directly connected to the B+ line 402. The second base electrode
422 is connected through a resistor 427 to ground. The second base
electrode 422 of the unijunction transistor 421 is connected
through a capacitor 443 to the base electrode 449 of the transistor
447.
A resistor 445 is connected between the base electrode 449 of the
transistor 447 and ground. The emitter electrode 448 of the
transistor 447 is directly connected to ground. The collector
electrode 450 of the transistor 447 is connected through a resistor
445 to the common B+ line 402. The base electrode 433 of the
transistor 431 is directly connected to the collector electrode 412
of the transistor 409. The collector electrode 434 of the
transistor 431 is directly connected to the common B+ line 402. The
emitter electrode 432 of the transistor 431 is connected through a
resistor 437 to ground. A capacitor 439 is connected in parallel
with the resistor 437. A variable capacitor diode 441 has its anode
connected to the emitter electrode 432 of the transistor 431 and
the cathode of the variable capacitor diode 441 is connected to the
collector electrode 464 of the transistor 461. A resistor 453 is
connected between the B+ line 402 and the base electrode 463 of the
transistor 461. A resistor 467 is connected between the base
electrode 463 of the transistor 461 and ground. A capacitor 462 is
connected in parallel with the resistor 467. A resistor 469 is
connected between ground and the emitter electrode 462 of the
transistor 461. A feedback capacitor 471 is connected between the
emitter electrode 462 of the transistor 461 and the collector
electrode 464 of the transistor 461. A coil 501 is connected
between the collector electrode 464 of the transistor 461 and one
terminal of the resistor 455. A capacitor 457 is connected between
the junction of the resistor 455 and coil 501 and ground. The
radiating antenna 13 of the transmitter is connected to a tap on
the coil 501.
Referring to the operation of FIG. 5. The resistor 401 is a rate
control which varies the voltage applied to the base 409 of the
transistor to the base electrode 411 of the transistor 409, thereby
varying the collector current of the transistor 409, the higher the
collector current in 409, the faster capacitor 417 charges. As
capacitor 417 reaches approximately 60 173 percent of the supply
voltage, the unijunction transistor 421 discharges capacitor 417
and hence the output of the emitter of the unijunction transistor
421 is a sawtoothed wave. This sawtooth wave form is applied to the
base of transistor 431 and the emitter follower's transistor 431,
emitter 432 has the same sawtooth wave on it as is applied to the
base 433 except with a higher current value. This sawtooth wave is
applied to variable capacitance diode 441 which in turn is
connected to the tank circuit of the oscillator 461. As the
sawtooth voltage changes so does the capacitance of the variable
capacitor diode 441, thereby changing the resonant frequency of the
transmitter and frequency modulating it from 280 megaHertz to 270
megaHertz. Capacitor 439 provides an RF return path for the
variable capacitance diode 441. When the sawtooth reaches its limit
and the unijunction transistor 421 fires, a brief positive voltage
pulse is applied across resistor 427. This pulse is conducted
through the capacitor 443 turning on the transistor 447 which
shorts the oscillator out of conduction. This shorting of the
oscillator out of conduction forms a blanking pulse on the base
pulse rate of the oscillator which, in this case, varies from 1
kiloHertz to 100 kiloHertz. Stating this concept another way. When
transistor 447 turns on, it momentarily shorts to ground the
oscillator. Another way to say it is it increases the voltage drop
across the resistor 455 to the point where the transmitter ceases
to oscillate. The complete process is repetitive at a rate set by
the rate control 401 which controls the rate at which the
transistor is blanked.
The FM rate is set by the rate control which controls the rate of
change of voltage across capacitor 417 and the total deviation of
this voltage. The frequency limits are chosen by the voltage
actually appearing at the emitter electrode 432 of transistor 431
which is a function of the type of unijunction transistor and by
the choice of the variable capacitor diode 441 and its capacitance
change for a given applied voltage. The frequency sweep between the
higher value of frequency, 280 megaHertz, and the lower value of
frequency, 270 megaHertz, is caused solely by the variable voltage
diode 441 which is across the tank circuit of inductor 501 and
capacitor 457 and this changes the resonant frequency of the tank
circuit and hence the output frequency of the oscillator.
In the case where the transmitter of FIG. 5 is on an operative
location then the FM signal is received by two paths to the
receiver antenna 19. One will be a direct path and one will be a
reflective path being reflected from objects or people around or
near the site of the transmitter. Since the directly received path
is the shortest path, any signal arriving by the reflective path
will arrive at a later time. Since we are using an FM signal, which
varies in frequency, with times from 280 megaHertz to 270
megaHertz, there will be a difference note generated by the direct
and reflected waves when they are mixed together. The difference in
this note will be determined by the rate control of the FM
transmitter which is preset and by the distance of the reflecting
objects. If these objects happen to lie at the distance at which a
difference note of the desired frequency is produced, it will be
passed by the 10 kiloHertz tuned amplifier transistors 121, 131,
141, 139 and 165. From this point on, it is rectified by the second
detector 29 comprising diode 175. The remainder of the operation of
the receiver is exactly the same as in the first description
thereof.
However, if an intruder enters the RF field, nothing will happen
until he gets at the proper distance from the transmitter and
receiver combination, so that the difference note he produces will
be within the range of the tuned amplifier. This tuned amplifier,
as previously mentioned, is at 10 kiloHertz tuned frequency. When
the intruder gets within this small zone then he will disturb the
10 kiloHertz difference note by disturbing the RF field, the
amplitude will drop off, therefore the input to the amplifier 27
will decrease from this point. The operation is again the same as
the intrusion alarm described before. The other case will be if the
intruder enters within this zone so as to produce a 10 kiloHertz
difference note of increased amplitude and the signal into the
amplifier increases and again the operation is the same as the
intrusion alarm heretofore discussed. To further clarify the
operation of the receiver, the direct FM signal which arrives
directly from the transmitter has its frequency component different
than that which arrives from the reflective wave due to the
increase in path. The two signals as received across diode 107 are
mixed together so there is an output signal which is a difference
signal, either below 7 kiloHertz, the bottom threshold of the tuned
section, or above 13 kiloHertz. However, if the difference signal
is below 7 kiloHertz or above 13 kiloHertz, then the alarm cannot
be set off. If the object which is causing the reflections is at
such a distance that it causes a difference signal between 7
kiloHertz and 13 kiloHertz, then the amplifier can then perform as
described for FIGS. 3 and 4. The thing which causes the receiver to
have a 7 to 13 kiloHertz difference frequency is a certain
prescribed distance that the intruder is between the units. This
distance can be determined by experiment in a field application or
determined by setting the rate control. As a practical matter, this
distance will describe an ellipse, and it will be the periphery of
an ellipse. In other words, as the rate control of the transmitter
is varied, then the distance from the receiver to the transmitter
and the point at which the intruder enters to give, say, an 8
kiloHertz signal, can be accurately determined. By varying the rate
control of the transmitter, the periphery, or the distance, from
the transmitter to the intruder is changed for the prescribed
signal difference needed to set the transmitter off. As previously
mentioned, the alarm only responds to signals in the 10 kiloHertz
region or to mixed different signals produced in the 10 kiloHertz
region. In order to produce a difference signal in the 10 kiloHertz
region, the intruder must be at such a distance from the
transmitter and receiver in combination so that the path from the
transmitter antenna to the reflecting body and back to receiver
antenna is limited by an amount determined by the sweep rate of the
transmitter. If the sweep rate of the transmitter is increased then
the intruder must get closer to the receiver and transmitter. If it
is decreased then he would have to be further away to produce the
same difference signal. Again, the pattern or zone semi-circular
zone of protection around the receiver and transmitter will be an
ellipse with the foci at the transmitter antenna and the receiver
and transmitters. The thickness of this band of protection may be
varied by changing the tuned 10 kiloHertz filters bandwidth from
the 7 to 13 kiloHertz. If it is, if the bandwidth is very wide,
then we would have a wide zone of protection about the periphery.
If the bandwidth is narrow, then the peripheral zone of protection
is narrower. The advantage of this operation of the alarm is that
in effect, people may move inside the circle of protection. In
other words, people may move around and about the alarm unit
without setting it off. People may also move outside the zone of
protection without setting it off, but nobody can cross the zone
without triggering the alarm.
Obviously, many modifications and variations of the present
invention are possible in the light of the above teaching. It is
therefore to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described.
* * * * *