Diagnostic system for the present or predicted structural condition of a mechanical bearing unit installed on wheeled equipment suited and intended to be located on and moved by rolling on a track in the longitudinal direction thereof, in particular a railway car ▪ comprising: ∘ a means for measuring the value of a parameter of the rolling conditions of the mechanical bearing unit characteristic of the structural state thereof, onboard the wheeled equipment and matched with the mechanical bearing unit, suited for measuring the value of the parameter and providing data characteristic of the rolling conditions and a means for calculation and analysis, suited, starting from the characteristic data, to provide diagnostic information on the present or predicted structural condition of the mechanical bearing unit, ∘ a point, directional transmitting antenna, onboard the wheeled equipment suited for transmitting the characteristic data or the diagnostic information in a main transmission direction and a main emission lobe, ∘ a point, receiving antenna, suited to receive the characteristic data or diagnostic information characterized in that ▪ the point, receiving antenna is structurally disassociated from the wheeled equipment and located in or near a communication area for the track, relative to the track and the wheeled equipment, is arranged so as to be located in the main transmission lobe of the transmitting antenna at the moment when the wheeled equipment, in particular at the moment when the transmitting antenna, passes or is located in the communication area for the track, and in that ▪ the transmitting antenna is positioned relative to the wheeled equipment and the track with the main transmission direction oblique relative to the longitudinal direction in the communication area (LDCA), and where the main transmission lobe crosses the receiving antenna at an angle, whereby, when the wheeled equipment moves on the track and everything else is equal, the time during which the receiving antenna is located in the main transmission lobe is increased. ▪ comprising: ∘ a means for measuring the value of a parameter of the rolling conditions of the mechanical bearing unit characteristic of the structural state thereof, onboard the wheeled equipment and matched with the mechanical bearing unit, suited for measuring the value of the parameter and providing data characteristic of the rolling conditions and a means for calculation and analysis, suited, starting from the characteristic data, to provide diagnostic information on the present or predicted structural condition of the mechanical bearing unit, ∘ a point, directional transmitting antenna, onboard the wheeled equipment suited for transmitting the characteristic data or the diagnostic information in a main transmission direction and a main emission lobe, ∘ a point, receiving antenna, suited to receive the characteristic data or diagnostic information characterized in that ∘ a means for measuring the value of a parameter of the rolling conditions of the mechanical bearing unit characteristic of the structural state thereof, onboard the wheeled equipment and matched with the mechanical bearing unit, suited for measuring the value of the parameter and providing data characteristic of the rolling conditions and a means for calculation and analysis, suited, starting from the characteristic data, to provide diagnostic information on the present or predicted structural condition of the mechanical bearing unit, ∘ a point, directional transmitting antenna, onboard the wheeled equipment suited for transmitting the characteristic data or the diagnostic information in a main transmission direction and a main emission lobe, ∘ a point, receiving antenna, suited to receive the characteristic data or diagnostic information characterized in that ▪ the point, receiving antenna is structurally disassociated from the wheeled equipment and located in or near a communication area for the track, relative to the track and the wheeled equipment, is arranged so as to be located in the main transmission lobe of the transmitting antenna at the moment when the wheeled equipment, in particular at the moment when the transmitting antenna, passes or is located in the communication area for the track, and in that ▪ the transmitting antenna is positioned relative to the wheeled equipment and the track with the main transmission direction oblique relative to the longitudinal direction in the communication area (LDCA), and where the main transmission lobe crosses the receiving antenna at an angle, whereby, when the wheeled equipment moves on the track and everything else is equal, the time during which the receiving antenna is located in the main transmission lobe is increased.