| 摘要 |
1360000 Selective signalling BRITISH RAILWAYS BOARD 8 Nov 1971 [13 Nov 1970] 54148/70 Heading G4H In a FDM signalling system, signals of frequencies f n are derived from oscillators Rt n and are fed together with a carrier signal from an oscillator 10 into respective modulators M n from which they are passed along a transmission line 12 to respective demodulators D n fed from the oscillator 10 and to filters Rr n , Rl n , Rr n may be high Q resonant reed generators/receivers (or any other suitable mechanical or electromechanical resonant system) and M n , D n may be suppressed carrier (de)modulators. It is stated that this arrangement ensures that a receiver for one frequency will not pick up signals of another frequency and that the line amplifiers required to maintain the signal level as it is transmitted do not require a large relative bandwidth. The oscillator 10 may be replaced by individual identical ones obtained by multiplication of the A.C. supply frequency. More than one carrier may be operated on the same line 12. |
