A digital radio modem for the modulation and demodulation of a digital signal, in accordance with a preselected radio access technology, said digital radio modem comprising a protective frame of overall parallelepipedic design and a plurality of communication interfaces which are arranged within said protective frame, Said digital radio modem being characterized in that the plurality of communication interfaces comprises: at least two first communication interfaces with a complementary device, one of the first communication interfaces comprising: - on one of the surfaces of the protective frame, described as the "upper surface", two male SPI connectors (203, 203'); another of the first communication interfaces comprises: - on the opposing surface of the protective frame to said upper surface, described as the "lower surface", two female SPI connectors (205, 205'), which are designed to cooperate with the two male SPI connectors (203, 203') of another digital radio modem such that, when a plurality of digital radio modems are connected, the male (203, 203') and female (205, 205') SPI connectors constitute the respective terminations of at least one SPI data bus, arranged internally to the protective frame, and employed by the digital radio modem for the transmission and reception of data to and from the digital radio modem(s) to which it is connected; at least one second communication interface with an analog radio interface module, the second communication interface comprising: on one of the lateral surfaces of the protective frame, described as the "rear surface", at least one other SPI connector and at least one coaxial connector, which are designed to cooperate with the complementary connectors present on an analog radio interface module. at least two first communication interfaces with a complementary device, one of the first communication interfaces comprising: - on one of the surfaces of the protective frame, described as the "upper surface", two male SPI connectors (203, 203'); - on one of the surfaces of the protective frame, described as the "upper surface", two male SPI connectors (203, 203'); another of the first communication interfaces comprises: - on the opposing surface of the protective frame to said upper surface, described as the "lower surface", two female SPI connectors (205, 205'), which are designed to cooperate with the two male SPI connectors (203, 203') of another digital radio modem such that, when a plurality of digital radio modems are connected, the male (203, 203') and female (205, 205') SPI connectors constitute the respective terminations of at least one SPI data bus, arranged internally to the protective frame, and employed by the digital radio modem for the transmission and reception of data to and from the digital radio modem(s) to which it is connected; - on the opposing surface of the protective frame to said upper surface, described as the "lower surface", two female SPI connectors (205, 205'), which are designed to cooperate with the two male SPI connectors (203, 203') of another digital radio modem such that, when a plurality of digital radio modems are connected, the male (203, 203') and female (205, 205') SPI connectors constitute the respective terminations of at least one SPI data bus, arranged internally to the protective frame, and employed by the digital radio modem for the transmission and reception of data to and from the digital radio modem(s) to which it is connected; at least one second communication interface with an analog radio interface module, the second communication interface comprising: on one of the lateral surfaces of the protective frame, described as the "rear surface", at least one other SPI connector and at least one coaxial connector, which are designed to cooperate with the complementary connectors present on an analog radio interface module.