| 摘要 |
1525324 Selective signalling MOTOROLA Inc 24 May 1976 [26 June 1975] 21457/76 Heading G4H A battery saver circuit for use with personalized radio apparatus powers receiver means to look for a first signal for a first time duration and in response to detecting it powers the receiver means to look for a second signal for a second, shorter, time duration. A plurality of personal paging receivers can be called up by radio by sending a sequence of tones (modulated on to a carrier), the sequence consisting of a long first (preamble) tone common to the plurality (though not in general to other receivers) followed by a gap followed by, for each receiver in turn, 2nd-6th tones and the presence or absence of a longish additional tone. In each receiver, the sequence is demodulated and fed to a switchable tone filter and detector which is controlled to look for the preamble tone. If this is detected three times, the remaining tones appropriate to the receiver are looked for in turn but if one is not detected, the receiver returns to looking for the second tone. If all the tones, with the possible exception of the additional tone, are detected, an audible alert signal is generated, having one of two frequencies according to the presence or absence of the additional tone. Detect time windows for the tones have durations according to: "preamble" greater than "additional" greater than each of the others. Power (battery) is switched to the (demodulator) receiver circuits prior to the filter and to the filter and detector during spaced time periods only, until the preamble tone is detected when the period is repeatedly extended with each detection until following the third detection it is extended sufficiently to consider the first two "second" tones and on detecting the relevant "second" tone is extended further by a duration sufficient to extend over the next two "second" tones. |
