| 摘要 |
An FM communication system in which AM modulation, applied to narrowband FM modulated signal, effects an improvement in power use and audio fidelity in portable units. By use of an AM scheme, radiated power is enhanced at frequency extremes to counteract the effects of narrowband FM systems while radiated power is minimized for low amplitude, modulating signals associated with limited carrier frequency deviations. As the amplitude of the signal to be transmitted decreases during quiet intervals, the power of the transmitted FM signal correspondingly decreases. A corresponding remote battery powered unit and a base unit are typically provided. Each includes an FM-AM transmitter. The power of the transmitted signal from the remote unit is adjusted according to the signal level received from the first unit, to compensate for signal levels lost over long distances and avoid unnecessary power drain for short distances and low information content situations. The system typically utilizes infrared light as the transmission medium. Pulse activation of infrared emitting diodes with the FM-AM modulated signal to provide limited range and thus privacy. |
