| 摘要 |
PROBLEM TO BE SOLVED: To obtain a transmission signal detecting device having a simple configuration, and capable of changinging the handset of a telephone set to another one in accordance with a transmission signal outputted by the telephone set and outputting a signal notifying the outside about the incoming, speech communication and calling states of the telephone set, and to obtain a hand-free device using the device. SOLUTION: In this transmission signal detecting device, an antenna in constituted with a signal line connected to a telephone set main body, a transmission signal transmitted from a telephone set is received by the antenna and the transmission signal is supplied to a detecting part 3, and, the length of the antenna is defined as about 1/2 wavelength of the carrier of the transmission signal. In this hand-free device, the transmission signal detecting part 3 is constituted of the transmission signal detecting device, and the transmission signal detecting part 3 outputs a detection signal synchronizing with the detection of the carrier of the transmission signal.
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