| 摘要 |
PURPOSE:To attain low cost by utilizing an oscillation frequency of a spare modulator as a local oscillation frequency of the reception side and selecting the frequency of the spare system modulator so that the difference between transmission/reception frequencies is a constant value thereby simplifying the circuit constitution. CONSTITUTION:When f1, f'1 are used correspondingly, the 1st FM modulator 3 is used as a transmission modulator, an output signal of the 2nd FM modula tor 4 is fed to a mixer 9 via an RF switch 5', the mixer is used in place of a conventional reception local oscillator. When f2 and f'1 are used corresponding ly, the 2nd FM moculator 4 is used as a transmission modulator and the 1st FM modulator 3 is used in place of a conventional local oscillator. When the f1 and f'2 are used correspondingly, a difference ¦f1-f'2¦ is used as an intermedi ate frequency, and the f2 and f'2 are used correspondingly, a difference ¦f1-f'1¦ is use as the intermediate frequency. Thus, no effect is given on a circuit using the IF frequency and succeeding circuits even if a radio frequency is changed by assigning the frequency according to the relation of ¦f2-f'2¦=¦f1-f'1¦. |
