FINAL REPORT - Stakeholders - Ofcom

Figure 3-9: Required spectrum limits for Mode S transponder transmitter
3.3.5.2 Out-of-band (OoB) Regulation
Both SSR and ACAS are ‘safety-of-life’ systems, meaning that frequency protection is
vital. In practice, this entails regulation and standardisation of ARNS in neighbouring
channels (e.g. DME).
SSR frequencies fall in the middle of ITU’s allocation to ARNS (960-1215MHz). As such,
regulation that takes place is between aeronautical regional navigation services. In
particular, the siting of DMEs and their equivalent frequency setting must be considered,
so as to maintain the strict protection from OoB interference in the 1090/1030MHz bands.
The military also has applications in this band (960-1215MHz) – military identification
systems (some of which ‘frequency-hop’) such as JTIDS (Joint Tactical Information
Distribution System) are the best examples. However, any such use is secondary to the
primary purpose of the band (ARNS), and strict regulations guarantee minimal
interference from these systems.
3.3.5.3 Summary of regulation
ICAO’s position is to recommend the reservation of the two frequencies for the
foreseeable future and this view appears to have general support from other aeronautical
stakeholders (i.e. airlines, service providers etc).
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