| 摘要 |
<p>A trainable transmitter for learning the characteristics of a received RF signal and for transmitting a coded RF signal having the learned characteristics to a receiver for remote activation of a device, such as a garage door opener. The trainable transmitter includes a tunable RF circuit and a controller coupled to the RF circuit for selectively tuning the RF circuit during a training sequence. To provide a user with an early indication that a valid RF signal is being received at the initiation of the training sequence, the control circuit quickly sweeps the frequency at which the RF circuit is tuned from the lowest frequency to the highest frequency of a frequency range in which the carrier frequency of a valid RF signal would fall. If a signal is not detected during this initial fast scanning procedure, the training sequence is terminated and the user is so informed.</p> |
