| 摘要 |
<p>A system (10) for remote control of performance of a function includes a portable transmitter unit (14) and a receiver unit (18). In one embodiment, the system (10) is a remote vehicle system. The transmitter unit (14) transmits a signal (16). The signal has a RF frequency at an unknown value within a range of values and conveys a message that contains a function request. Within the receiver unit (18) is superheterodyne circuitry (32) that has a mixer (44). The mixer (44) mixes a RF signal (42) coming from an antenna (28) and a reference frequency signal from a reference oscillator (46), and outputs an intermediate frequency signal (50) conveying the message. A bandpass filter (66) filters the intermediate frequency signal to pass a range of frequency values smaller than a known range of intermediate frequency values. Tuning control circuitry (70) automatically sweeps the bandpass range of the bandpass filter (66) over the intermediate frequency range. Passage detector circuitry (72) senses the intermediate frequency signal passing through the bandpass filter (66) and automatically causes the sweeping of the bandpass range to stop.</p> |
