Doppler radar sensor of moving objects. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Doppler radar sensor for moving objects DMS-4 © RINTEL. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Security devices and object signaling

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The DMS-4 sensor is intended for use in security, signaling and automatic control systems for various objects (for example, gates, etc.).

Specifications.
- supply voltage 9 ... 12 volts
- consumed current no more than 20 mA
- the minimum size of the registered object is 0.3 m
- range of speeds of movement of registered objects
from 0.1 to 10 m/s
- ambient temperature from -25 to + 60 degrees
- range: human detection up to 6 m, detection
car up to 30 m
- operating frequency about 900 MHz
- radiation power not more than 0.5 - 1 mW

The sensor consists of a microwave generator based on a KT371 (KT368) transistor, a pre-amplifier based on a KT3102 (KT315) transistor, and a comparator based on a K554SA3 chip. The microwave signal generated by the generator is emitted by a whip antenna and, after reflection from a moving object, receives a frequency shift equal to DFref = 2*V*Fred/C, where V is the speed of the object, C is the speed of light, F is the transmission frequency. The signal reflected from the object is received by the same antenna and in the microwave generator, which in this case works as a direct conversion receiver, is converted into a low (subsonic) frequency signal. In fact, the generator works like an autodyne. The resulting low-frequency oscillations are amplified by a preamplifier and then converted into rectangular pulses in a comparator. In the absence of reflected signals, the voltage at the output of the comparator is high. The tuning capacitor in the microwave generator circuit serves to set the frequency equal to the resonant frequency of the antenna (selected according to the maximum sensitivity of the sensor).

Structurally, the sensor is made on fiberglass printed circuit board and is located in a plastic case, the antenna (a piece of hard wire) is soldered to the contact pad of the board and comes out through a hole in the case. The recommended antenna position is vertical. There must be no shielding objects directly near the sensor.

(click to enlarge)

Author: Sai Oleg, (RA3XBJ); Publication: N. Bolshakov, rf.atnn.ru

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