Metaids operations in the band 400.1 to 406 MHzThis frequency band is very good for low power communications and as such meteorologists will have difficulty to retain sole use of the band in future.
Metaids operations between 400.15 and 406 MHz • Navaid radiosondes [Loran-C or GPS] • relatively small ground system antenna, usually no moving parts • occupied bandwidth minimum of 300 kHz for Loran • GPS capable of much smaller bandwidth with next generation radiosondes probably less than 100 kHz. • secondary radars
Metaids operations between 400.15 and 406 MHz,but also :---- • secondary radar, radar, or radiotheodolite • larger directional antenna, • occupied bandwidth several MHz at minimum • In some cases, transmitters very unstable in flight and do not remain within allocated bandwidth for service
Usage of systems • About 60 per cent of civilian radiosonde systems • as many military users as civilian of GPS radiosondes • sharing of with other services varies a great deal from country to country • many countries in Europe moving towards narrow band , less than 100 kHz operation
Modern GPS radiosonde with narrow bandwidth , stable frequency, frequency tuneable before flight
One type of radiosonde used widely in a national network for many years, but now being replaced , sample from 1989
Myth, all radiosondes are very old designs with very poor transmitter designs • Within a few years all radiosonde systems will have been modernised • necessary to ensure that all have good radiofrequency characteristics to allow use of spectrum to be optimised as desired by ITU and the meteorological satellite operators.
Sharing between 400.15 and 401 MHz Co -channel sharing is impossible with MetAids
401 to 403 MHz Co-ordination required with DCP operations of MetSat
Recent History • WRC 2000 proposal to allow MSS systems to operate between 405 to 406 MHz (Res. 219)was defeated • Expansion of MSS systems was too large to be considered viable by European Radiocommunication Agencies , who wished to retain spectrum for other use in future. Thus, MSS (USA, Indonesia) were defeated with strong help from CEPT and other agencies, but in future other requests for sharing will emerge. • Allocation studies show that spectrum necessary for radiosonde operations in a dense network should reduce from about 5 MHz to about 3 MHz with improved radiosonde transmitters by 2010
Current Concerns • Possibility of proposals for MSS use at frequencies below 1 GHz, under Res. 214 need to be guarded against. • No serious proposal has been produced at Study Group 7 or 8, but last minute interventions have happened before. • Necessary to prepare for the future and have a policy that allows some sharing with suitable systems in future. • New Vaisala radiosonde will have digital transmitter so all descriptions of main radiosonde in use will have to be changed at 400 MHz
Conclusion • Although USA (NWS) representatives had to lead the proposal for the MSS allocation at 405-406 MHz, friendly working relationships were retained between all the meteorological services and the proposal was defeated. • The UK also finds its national interests conflict with WMO policy, but the Met Office attempts to intervene in a manner beneficial to WMO interests, e.g. in the negotiations at 1680 MHz.