This invention relates to a cordless telephone system which consists of a radiophone and a radiostation wired to a communication line, wherein the radiophone and the radiostation include a radio transmitter and a radio receiver respectively.
FIG. 1 shows a system using a dial which is a typical prior system, in which A indicates a radiophone and B indicates a radiostation. The radiophone comprises a hand set 50, a dial 51 (or a keyboard), a low frequency oscillator 52 connected with the dial (51), a radio transmitter 53, a radio receiver 54, a voice amplifier 55 and also a hook switch 56. A dialing signal, developed by operation of a dial (51), modulates a low frequency wave from a low frequency oscillator (52) which is emitted on a carrier by the radio transmitter 53. A sound signal from the hand set 50 is also emitted on a carrier wave by the radio transmitter 53. The radio station B comprises a radio receiver 60, a sound amplifier 61, a hybrid circuit for a telephone 62 connected to a telephone line 67, a dialing signal demodulator 63, a dialing relay 64, and a radio transmitter 65.
The dialing signal emitted from the radiophone is received by the radio receiver 60, demodulated in the dialing signal demodulator 63 and are then applied to the dialing relay 64 to generate intermittently in accordance with a rotation of a dial (51). Thus, this telephone system is able to communicate with a telephone at a destination side. The sound signals from the radiophone are received by the radio receiver 60 and transmitted to the telephone of a receiving side through the sound amplifier 61 and the hybrid circuit 62. When the telephone of the receiving side transmits sound signals, these signals are emitted on a carrier by the radio transmitter 65 to the radio receiver 54 where the signals are demodulated and transmitted to the hand set 50 through the sound amplifier 55.
With such a telephone system, problems of jamming, tapping, calling a wrong radio-station and etc., may occur because of using radio communication. To prevent these problems, an electric wave of different frequency is employed for each of the devices.
However, it is easy to expect that these problems will occur more frequently, when this cordless telephone equipment or system will be in broad use.