| 摘要 |
PURPOSE:To improve the sensitivity of a receiving circuit, by removing multiple spurious components of frequency nearly equal to reception carrier frequency in a transmitter and receiver used for a wireless interphone capable for duplex transmission. CONSTITUTION:On a receiving circuit side 5, reception is performed at desired reception carrier frequency fB through an antenna 2 and at a front end 11 which uses the 9-multiplication output of a multiplying circuit 10 which multiplies the reference frequency f0 of a reference oscillating circuit 1 as a local oscillation input, high frequency amplification and frequency conversion are carried out. Its output is demodulated by a demodulating circuit 12 and then amplified by an amplifying circuit 13 to a necessary level and a speaker 14 converts the electric signal into a sound output, thus obtaining the sound output. Said reception carrier frequency fB is between a 7-multiple and an 8-multiple spurious component of a transmitting circuit, so a trap circuit 6 attenuates those 7- multiple and 8-multiple spurious components. |
