| 摘要 |
PROBLEM TO BE SOLVED: To reduce the number of parts and to attain miniaturization by means of processing the reception of a plurality of frequency bands in a common circuit by up-converting a low frequency signals to match with a high frequency signal. SOLUTION: When receiving the signal of two frequency band, that is, an L-Band and a VHF band, the signal of the 174-245 MHz VHF band separated by a duplexer 101 is synthesized with the local oscillation signal of 126.992 MHz, which is generated by a PLL circuit 131, by means of a mixer 141 and only a 1443.992-1514.992 MHz convert signal passes through a BPF 122 and is up-converted. Then it is selected by a change-over switch 102, passes through an LNA 112 and the BPF 123, is combined with the local oscillation signal of 1230.992-1301.992 MHz, which is generated by the PLL circuit 132, by means of the second mixer 142 and converted into an intermediate frequency signal of 213 MHz. Then a disturbance wave is removed by a band-pass filter 124, combined with the local oscillation signal of 215 MHz from the PLL circuit 133, converted into a signal of 2 MHz and outputted to a demodulating circuit. |
