| 摘要 |
PURPOSE:To prevent the mis-information of a call tone at reception standby by providing the 1st and 2nd cut-off frequency to the loop filter of a PLL constituting a carrier oscillating circuit and selecting the 2nd cut-off frequency at calling from an opposite station. CONSTITUTION:A wireless talking device consists of a transmission circuit section 1 transmitting a radio signal modulated by voice and a reception circuit section 2 demodulating a reception signal and outputting a voice. The carrier generating circuit 3 of the transmission section consists of the PLL circuit, the phase of a frequency f' to which the output frequency of a VCO30 is frequency-divided 31 and that of an audible frequency fs from a basic oscillation circuit 32 are compared (33), and a signal passing through a loop filter LF34 from the output controls the VCO30. As the cut-off frequencies of the LF34, a frequency f1 lower than the fs and a frequency f2 higher than the fs are provided. When the filter switching circuit 35 selects the frequency f2 at calling of an opposite station, the carrier set to the f2 is transmitted, the frequency fs superimposed on the carrier is demodulated at the opposite reception station and outputted as a call tone from a speaker 25 as a tone signal. |
