active as its sister organisation, the CCITT, as can be seen from Figure 22.5 which compares their standards output over a twenty year period. This is partly due to the fact that whereas the Volume Description CCITT devotes about 90% of its time to standards preparation, the CCIR devotes about 40% of its time to this, the rest being used on Spectrum utilisation and monitoring other studies, such as on spectrum utilisation. Space research and radio astronomy service The CCIR works through a series of Study Groups, similar to Fixed service at frequencies below about 30MHz those of the CCITT. Study Groups are nominated at Plenary meet- ings and the scope of their responsibility defined. They set up Fixed satellite service Working Parties to prepare draft Recommendations for consider- IV/IX -2 Frequency sharing and coordindation between ation by the Study Groups. For urgent topics smaller Task Groups systems in the fixed-satellite service and radio may be assigned the work, the Groups being disbanded when this relay systems has been completed. Study Groups have the authority to adopt draft Recommendations between Plenary Assemblies. Propagation in non-ionized media Table 22.4 shows the Study Groups over the period 1990 - 1994, Propagation in ionized media and Table 22.5 shows the CCIR/CCITT Joint Study Groups. These Standard frequency and time signals were set up at the XVIIth CCIR Plenary Assembly in Dusseldorf in 1990. The next Plenary is to be held in 1994. Table 22.6 gives the Mobile radiodetermination and amateur services content of the CCIR 1990 Recommendations. including the associated satellite services The XVIIth Plenary Assembly examined results of work by the IX - 1 Fixed service using radio relay systems Study Groups since the previous Plenary Assembly. Sixty new Recommendations were approved and 126 revised. This brought the Broadcasting service (sound) total in force up to 378. Major areas considered were: high defini- X/XI - 2 Broadcasting satellite service (sound and tion television, where five new Re