INFORMATION TRANSMITTING SYSTEM

PURPOSE:To ensure detection of collision of carrier band signals by detecting independently the presence of a different frequency component corresponding to a different signal level of a base band signal or its coded signal to detect that plural frequency components exist at the same time. CONSTITUTION:Plural MODEMs 6 are connected to the network, BPF12, 15 are connected respectively to an FM modulator 11 and an FM demodulator 16 of each MODEM6, a transmission amplifier 13 is connected to the BPF12 and a reception amplifier 14 is connected to the BPF15. A collision detector 17 connected to a collision display signal generating circuit 18 is connected to the BPF15. The detector 17 is provided with BPF20, 21 inputting a signal from the BPF15, each signal level is extracted and envelope detectors 22, 23 detect the signal. The signal is fed to comparators 26, 27, compared with a reference signal from reference signal generators 24, 25, the frequency component to each signal level is detected independently, an output of the comparators 26, 27 is fed to an AND circuit 28 to detect surely the collision of the carrier band signals.