scope:

The present document provides part 4 of the technical specifications for Very High Frequency (VHF) Digital Link (VDL) Mode 4 ground-based radio transmitters and receivers for air-ground communications operating in the VHF band, using Gaussian-filtered Frequency Shift Keying (GFSK) Modulation with 25 kHz channel spacing and capable of tuning to any of the 25 kHz channels from 118,000 MHz to 136,975 MHz as defined in ICAO VHF Digital Link (VDL) Standards and Recommended Practices (SARPs) [8].

The present document is designed to ensure that equipment certified to it will be compatible with the relevant ICAO VHF Digital Link (VDL) Standards and Recommended Practices (SARPs) [8] and VDL Mode 4 Technical Manual (TM) [1].

Manufacturers should note that in future the tuning range for the ground transceivers may also cover any 25 kHz channel from 108,000 MHz to 117,975 MHz.

The scope of the present document is limited to ground stations. The equivalent specification for airborne stations is EN 302 842 [7].

A description of the scope of the VDL Mode 4 system is provided in part 2 of these technical specifications (see EN 301 842-2 [5], clause 1).

EN 301 842-1 [4] deals with tests of the physical layer, EN 301 842-2 [5] deals with core link layer functionality and EN 301 842-3 [6] with additional broadcast functionality. The present document deals with tests of the datalink layer (DLS) and the link layer sufficient to support point-to-point functionality. Note that, as described in EN 301 842-2 [5], a system supporting point-to-point functionality is required to conform to EN 301 489-22 [2], EN 301 842-1 [4], EN 301 842-2 [5] and the specification in the present document

The present document includes:

• references, definitions, abbreviations and symbols are provided in clauses 2 and 3;

• clause 4 describes the VDL Mode 4 ground station point-to-point functions;

• clause 5 performance specifications for the VDL Mode 4 ground station;

• clause 6 provides general design requirements;

• clause 7 provide protocol tests for the point-to-point functions of the system;

a document history is contained in clause 8;

• clause A provides a detailed cross-reference to the relevant requirements contained in [1].

Note that the system can support a very wide range of functions. It is not practical to provide specific tests for all aspects of functionality. The approach used is to provide detailed tests for the core point-to-point functionality and to provide tests of those remaining requirements which, if wrongly implemented, could cause a deterioration in the service offered by other VDL Mode 4 stations.

Mandating and Recommendation Phrases

a) "Shall":

- the use of the word "Shall" indicates a mandated criterion; i.e. compliance with the particular procedure or specification is mandatory and no alternative may be applied.

b) "Should":

- the use of the word "Should" (and phrases such as "It is recommended that...", etc.) indicates that though the procedure or criterion is regarded as the preferred option, alternative procedures, specifications or criteria may be applied, provided that the manufacturer, installer or tester can provide information or data to adequately support and justify the alternative.