The present document specifies the minimum performance parameters for terrestrial digital fixed service radio communications equipments operating in the 23 GHz frequency band and contains a complete revision in the areas of: - additional systems with higher spectrum efficiency in the new class 4 systems; - introduction of unique system type codes for regulatory reference to the various system types detailed in the present document@ refer to new annex C and related categories of equipment classes of spectral efficiency; - change of spectrum mask and adjacent channel selectivity of STM-0 systems in 28 MHz channel spacing to align to EN 300 639 [33]; - introduction of new spectrum efficiency class 5 for STM-1 capacity for 28 MHz Adjacent Channel Alternate-Polarization (ACAP as class 5a) and Adjacent Channel Co-Polarization (ACCP as class 5b)@ see examples of the spectrum usage in figures 1.1a and 1.1b; NOTE: In a previous version of the present document there was provision for: - parameters for wideband analogue systems; - further options for digital radio systems (there referred as Grade A systems); - specific antenna radiation patterns (now superseded by EN 300 833 [3]). These options are not reprinted in this version as they are considered to be no longer of interest for ETSI members. However@ for regulatory purposes@ they may still be referenced from the previous version. Digital systems are intended to be used for point-to-point connections in local and regional networks at data rates between 2 Mbit/s and Synchronous Transport Module@ level 1 (STM-1). The parameters to be specified fall into two categories: a) those that are required to provide compatibility between channels from different sources of equipment on the same route@ connected either: - to separate antennas; or - to separate polarizations of the same antenna. b) parameters defining the transmission quality of the proposed system. The present document deals with Radio Frequency (RF) and baseband characteristics relevant to low@ medium and high capacity Plesiochronous Digital Hierarchy (PDH) transmission systems@ STM-0 and STM-1 Synchronous Digital Hierarchy (SDH) transmission systems. Antenna/feeder system requirements are covered in EN 300 833 [3] . The present document does not contain aspects related to test procedures and test conditions however they are to be found in EN 301 126-1 [2]. As the maximum transmission rate in a given bandwidth depends on system spectral efficiency@ different equipment classes are defined: class 2: equipment spectral efficiency based on typically 4-states modulation scheme (e.g. 4-FSK@ 4-QAM@ or equivalent); class 3: equipment spectral efficiency based on typically 8-states modulation scheme (e.g. 8 PSK@ or equivalent); class 4: equipment spectral efficiency based on typically 16 or 32-states modulation scheme (e.g. 16-QAM@ 32-QAM@ or equivalent); class 5: equipment spectral efficiency based on typically 64-states or 128-states modulation scheme (e.g. 64-QAM@ 128-QAM@ or equivalent). The above classes are indicative only and do not imply any constraint to the actual modulation format@ provided that all the requirements in the present document are met. Safety aspects will not be considered in the present document. However compliance to EN 60950 [34] will be required to comply with 1999/5/EC [35] Directive (RTTE). Technical background for most of the parameters and requirements referred in the present document may be found in TR 101 036-1 [30].