| 摘要 |
A method has the steps of generating a first control message having a plurality of message symbols and a first audio message to be transmitted from a first radio-communications device to a second radio-communications device. The first audio message is sampled to obtain a first plurality of audio samples, each with an instantaneous signal valve, and a first radio frequency signal which varies in frequency from a first predetermined radio frequency dependent on the instantaneous signal valves of the first plurality of samples is generated. The first radio frequency signal is formatted into a first pulsed radio frequency signal, each pulse having a time duration representative of one of the plurality of message symbols of the first control message, which is transmitted from the first radio-communication device to the second radio-communication device. A system is also provide wherein first and second radio-communication devices each include a radio frequency antenna, a frequency modulator to generate a first radio frequency signal which varies from a first predetermined radio frequency dependent on the instantaneous signal values of an audio signal provided thereto, and a first switch coupled to the antenna and the modulator to selectively couple the antenna to the modulator for a first predetermined duration, the duration of the coupling of the antenna to the modulator representative of a symbol of a control message to be communicated between the first and second radio-communication devices.
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