| 摘要 |
This disclosure relates to an intrusion detector having a microwave transmitter and receiver employing a single antenna. A transistor is interconnected through the inductive cavity of a coaxial line to define a Colpitts' oscillator for transmitting of energy of a given frequency into the area to be protected. The transistor is exposed to both the transmitted and the echo signal in the cavity. The non-linear characteristic of the transistor mixes the transmitted and the received signals and includes an output across an emitter resistor which is equal to the difference of the transmitter frequency and the echo frequency i.e., the Doppler frequency. The latter signal is amplified and actuates a Schmitt trigger circuit for controlling an alarm.
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