| 摘要 |
A point to multipoint two-way communications system in which a base station transmits to a remote station ("outstation") on a frequency derived by the base station from the frequency of a previous transmission received by said base station from said outstation. The outstation preferably transmits an FSK modulated data signal to the base station wherein, following reception of this signal, the channel is divided into a plurality of narrow frequency bands and the presence of data signals in each of these bands is detected. The detected signals are then demodulated by at least one narrow band filter centred on the detected status signal frequency bands and the data therein is extracted. Having ascertained the outstation's transmission frequency, the base station is then able to determine an associated transmission frequency for the downlink. Enables low power, low tolerance components to be used in outstation. |
