DIGITAL BROADCASTING SYSTEMS IN THE 87-108 MHZ BAND

 Interference management process between FM broadcasting and aeronautical services.

Frequency modulation (FM) broadcasting service interference to instrument landing systems (ILS) localiser, VHF omnidirectional radio range (VOR) and aeronautical VHF communications equipment has been a widely recognised problem for many years. 

The problems of interference to aircraft receivers is usually due to the following factors:

1. FM broadcasting stations operate with high-powers levels of up to 250kW erp, whereas aeronautical facilities in the adjacent band operate with power levels in the range 0.02-6kW erp;
2. FM broadcasting stations due to their high power levels transmit significant spurious emissions;
3. Some State regulation do not confirm to the new standard;
4. There is no guard-band between the highest assignable frequency for FM broadcasting (107.9 MHz) and lowest assignable radionavigation frequency (108.0 MHz).

The decision of the World Administrative Radio Conference (Geneva, 1979) to extend the FM broadcasting band to 108 MHz put aeronautical and broadcasting services in adjacent bands.  Recognising that this change might lead to interference problems, studies were carried out within the ITU Study Groups from 1982 to 1995 to determine the technical constraints to be used to achieve compatibility between the services.

At the Regional Administrative Conference for FM sound broadcasting in the VHF band (Region 1 and certain countries concerned in Region 3), Geneva 1984, compatibility criteria and assessment criteria assessment were agreed (called “Geneva Agreement, 1984” or GE84).  However, compatibility between the FM broadcasting frequency plan and the aeronautical radionavigation service frequency plan was not fully studied.  Also, no compatibility tests with the aeronautical mobile (R) service (117.975-137 MHz) were performed.  Further studies were carried out by the ITU-R study groups resulting in the approval of Recommendation ITU-R SM.1009-1 in 1995