| 摘要 |
PROBLEM TO BE SOLVED: To prevent excess transmission by extracting a reception level from a reception signal, adjusting master machine side impedance matching in accordance with the level and preventing matching in a high reception level position. SOLUTION: The reception signal in an antenna part 19 is demodulated in a reception part 15 through a variable adjusting part 23 executing impedance matching and a switch 16. An electric field intensity level received in a reception electric field detection part 22 is extracted from the demodulation signal and a control part 20 compares it with a reference electric field intensity level which is previously set. When a slave machine is near, the reception electric field intensity level is higher and a reception state is satisfactory, the control part 20 transmits a control signal so that the impedance matching of the matching part 23 is shifted form a reference value. Thus, a radio signal transmitted form the antenna 19 is reduced and reception sensitivity is reduced. In such a case, the reduction of the reception sensitivity of the antenna 19 can be prevented only by control at the time of transmission. |
