INFORMATION TRANSMITTING SYSTEM

PURPOSE:To improve the network efficiency by detecting collision of a carrier band signal through the change component of a beat signal produced due to collision of carrier band signals transmitted from plural MODEMs to ensure the detection of collision at each MODEM. CONSTITUTION:A carrier band transmission line 1 of the network is constituted of a transmission line 2, a reception line 3 and a head end 4 comprising a directional coupler and plural MODEMs 6a-6n are connected to the transmission line 1. The MODEMs 6a-6n are provided with a level change detecting circuit 17 detecting collision, a signal from an LPF of the pre-stage is detected by an envelope detection circuit 20 and the level signal of the said signal is fed to an LPF21 and an HPF24. One signal is fed to an AND circuit 27 via a delay circuit 23, a signal forming only the AC component is fed to a comparator 25 by other HPF24, the signal is compared with a reference signal of a reference signal generator 26, the signal level change is detected and the result is fed to the circuit 27. Then the collision of the carrier band signals is detected surely at each MODEM (6a-6n).