Patent GB-1331061-A (GB)
Title: Radar sensor
IPC: H04M11/04
Filed: 1970-10-09
Abstract: 1331061 Radar GARSIDE CORP 9 Oct 1970 [20 April 1970] 48083/70 Heading H4D [Also in Division G4] A radar sensor comprises a first antenna radiating energy from an oscillator into a monitored volume, a second electromagnetically shielded antenna, and a difference amplifier for sensing any variations in the difference voltage between the two antennµ. A stabilized D.C. voltage from an integrated circuit voltage stabilizer (Fig. 13, not shown) is applied to oscillator 98 via wire W38. As the positive voltage is applied to the middle of coil L8 one of the transistors Q64, Q66 conducts and the other respective capacitor C24, C22 charges. After a short time the procedure is reversed and oscillation at a frequency determined by the component values (e.g. 400 MHz.) is generated. Some of the energy is inductively coupled to two coils L2, L4, one of which L2 is completely enclosed in the sensor housing and the other of which L4 is connected to an antenna 18 situated in the surveillance area. Movements inside the surveillance area influence the antenna impedance which causes variation in the voltages induced in the coil L4. Variations in the difference voltage between the two coils L2, L4 is detected at wire W40 by an amplifier (96, Fig. 11, not shown) comprising discrete and integrated circuit amplifiers ending with an emitter follower whose rectified output supplies positive pulses to the alarm circuitry. The radar sensors are incorporated along with heat sensors (28), push-button alarms (24) for signalling hold-up robberies and "bill-traps" (22) which indicate when all currency has been removed from a cash register drawer in a complete alarm system (Fig. 1, not shown) which uses a computer dialler (12) to telephone pre-programmed numbers and transmit pre-recorded messages. An adapter (32) is also provided which on an alarm provides power for ancilliary equipment, e.g. lights, cameras and sirens. The system is supplied with a key switch (16) and optionally a seven-button decoder (14). The switch (16) is placed outside the protected building and operated by a key or is inside in which case the seven-button decoder is placed outside which on correct operation of three buttons disables the system temporarily enabling the authorized user to enter and switch off. Incorrect operation of any of the other four buttons automatically sounds the alarm. Computer dialler, Fig. 2.-Sensor detector 38 is connected to the radar sensors and feeds positive pulses, indicating movement, to a tape head switching circuit 52, which also receives alarm inputs from fire detectors and hold-up alarms. The sensor network may also be operated by incorrect operation of the seven button decoder. The key switch (16, Fig. 1, not shown) operates the alarm inhibit 42 to turn the burglar alarm system off and the seven button decoder when operated correctly operates disable circuit 44 to disable the sensor network for approximately two minutes. On receipt of any alarm pulses, switching circuit 52 starts the tape deck motor 78 via control 60 and further operates a relay to switch the audio amplifier 62 to the correct tape head. Amplifier 62 then provides 2500 Hz. tone bursts to rectifier 70 which triggers a 22 sec. monostable 79 if the burst lasts for more than 4 seconds. The monostable pulse enables the tone burst gate 82 which passes dialling pulses to relay switch 84. Relay switch 84 operates a relay in network 66 which opens the telephone line and passes the dialling pulses thereto. Pre-recorded messages pass from a second output of amplifier 62 to the telephone line 94. After a predetermined time tape deck stop circuit 76 stops the tape motor and the cessation of the tone bursts closes the telephone line. A test switch 64 is provided which operates dial inhibit 88, preventing dialling and also passes the recorded messages to loudspeaker 68. To prevent blocking of the telephone line when the system is being used, an interrupter circuit 86 detects when the user's telephone is being called. This circuit then temporarily opens the line and then closes it, effectively lifting the receiver and then replacing it. This facility is short-circuited by answer enable 90 when key switch (16) is off thus allowing normal usage of the telephone line.