A method and device is described for converting an STM-1 signal into a sub-STM-1 signal in synchronous radio transmission. The invention provides for the use of a pure regenerator network element without any multiplexing function. The method according to the invention provides in transmission, for reducing the received STM-1 signal by one third (only the first TUG-3 is considered as valid and is transmitted in the radio link, whereas the second and the third TUG-3 are considered in an unequipped condition and are not transmitted), thus maintaining the STM-1 structure. In reception, the method provides for reconstructing the signal with the complete regenaration of the payload and the correct structure of the AU-4 without incurring any parity control infringement.