This European Telecommunication Standard (ETS) defines the minimum technical requirements for terrestrial digital radio relay systems operating in the frequency range 24@25 GHz to 29@50 GHz. Digital systems covered by this ETS are intended to be used for point-to-point connections in local and regional networks at data rates between 2 Mbit/s and 155 Mbit/s. Typical applications include: a) network extensions; b) customer connections; c) inter-cellular links. For digital systems@ with capacities up to 34 Mbit/s@ two types of equipment are specified: - Grade A equipment@ intended for applications where moderate frequency congestion is envisaged; - Grade B equipment@ intended for applications where higher nodal capacity is required. The equipment covered by this ETS is intended to be used in systems designed to meet the appropriate error performance and availability objectives defined by ITU-T and ITU-R Recommendations. The parameters specified fall into two categories: a) those that are required to provide compatibility between Radio Frequency (RF) channels occupied by different sources of equipment at the same nodal point; b) parameters defining the equipment performance of the proposed system. This ETS deals with RF and baseband characteristics. As regards the Synchronous Transfer Module-level 1 (STM-1) signal@ the Section Overhead (SOH) processing is covered in ITU-R Recommendation 750 [19]. Rainfall is the main propagation factor limiting error performance in frequency bands above 20 GHz. Therefore distortion sensitivity is not likely to be significant for short haul operation. Signatures for systems are not specified. Safety regulations are outside the scope of this ETS.