nal Operator's requirements. 1. The number of mobile paging receivers must not exceed the Table 45.7 CCIR radiopaging code no. 1 number of mobiles in a system and each paging receiver must be used only in conjunction with a particular mobile station. 2. The normal base station transmitter power may not be in- Parameter Value creased. 3. The use of additional stations cannot be licensed solely on the Frequency 466.075MHz +50Hz (frequency offsets grounds that they are necessary for overlay paging. max. 1800Hz allowable) 4. The paging system must use the same type of modulation as that Deviation +4.0 or +4.5kHz depending on country of the mobile system in which it is employed. Channel spacing 20 or 25kHz depending on country 45.9.2 Revertive paging or secondary calling Transmission rate 1200 +10 Baud Signal rise time Revertive paging, or secondary calling, is an addition to PMR Character set Special characters e.g. umlaut (a, 0) are systems where paging addresses originating at the base station are both possible and permitted and will be received by the vehicle radio and retransmitted to a paging receiver specified by each country involved carried by the driver. 45.9.3 Private off site paging These are non public subscriber large area (up to 10 sq. miles) The disadvantage of this system is that since it utilises existing systems. To avoid interference between neighbouring small on site paging networks in each country, it is only possible to call a pager systems, alternative frequencies are chosen where available. In the somewhere in Europe through its own national base. UK, in order to minimise interference, manufacturers who are members of the Radio Paging Association, determine the appropri- ate channel by entering the ordnance survey coordinates of the 45.10.1.1 Transmission transmitter location into a data base of existing systems. It is possible though, for a group of adjacent sites to timeshare the same Time slotting of transmitters is used to ensure decoupling of ad- channel frequency. In the UK specific time