| 摘要 |
Provided a modulation circuit comprising a switch (13) for switching a Q-signal and a QX-signal, which are frequency-offset at a frequency offset unit (23), and a controller (18) for controlling a PC (32) to switch a local oscillation frequency and for controlling the switch (13) to interchange and feed the Q-signal and the QX-signal to a mixer unit (14). In case a local oscillation frequency (Flo) substantially coincident to the frequency of a jamming signal due to a digital signal component is set according to a desired frequency (Fdes) relating to the selection of a user, the local oscillation frequency is changed to leave far the frequency of the jamming signal, thereby to avoid the generation of a beat noise due to the jamming signal and to switch the phase at the time when the frequency mixing is made at the mixer unit (14), so that the frequency position of the image cancellation is changed to a position different from the frequency position of a desired wave signal. |
