| 摘要 |
A trainable transceiver for learning and transmitting an activation signal thatincludes an RF carrier frequency modulated with a code for remotely actuating a device, such as a garage door opener. In one embodiment, the trainable transceiver preferably includes a controller, a signal generator, and a dynamically tunable antenna having a variable impedance that may be selectively controlled in accordance with a carrier frequency of a received or transmitted activation signal. In another embodiment, the trainable transceiver preferably includes a phase-locked loop circuit for providing a frequency control voltage to a signal generator to selectively adjust the carrier frequency of the signal generator. In yet another embodiment, the trainable transceiver includes an amplifying circuit for selectively controlling the gain of a modulated radio frequency carrier signal received from the signal generator and for transmitting an amplified output signal to the remotely actuated device. In a further embodiment, the trainable transceiver includes a frequency table including a list of frequencies for remote transmitters known to transmit for only a short duration and the trainable transceiver first reads the short duration frequencies from the frequency table.
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