INTRODUCTION Transceiver Types FM 1200 and FM 1300 are digital signalling radios designed for use in trunked mobile networks. The equipment differs from the FM1100 analogue transceiver in that it is fitted with a Digital Signalling version (FFSK) of the Control PWB assembly. Apart from operational differences and descriptions of ancillaries normally found only on FM1200 and FM1300 radios, this Service Supplement provides information on the FFSK Control PWB assembly only. Although all standard FM1000 frequency bands can be supplied, the FM1200 radio is principally used on Band III (174 - 225MHz). It is fully approved to operate on the Band Three Radio Limited public network. These channel trunking systems allocate free channels to subscribers (for mobile-to-mobile or group calls) in real time. On completion of the call, the channel is made available for re-allocation to other subscriber calls. Call connection and channel allocation is controlled by the base control system. Fast Frequency Shift Keying (FFSK) digital signalling to MPT1327 and MPT1343 specifications is employed. FM1300 radios are designed for use on systems employing an extended version of the MPT1327 signalling protocol. For example, they allow manual channel selection for simplex or control channel working. A Non-Prescribed Data PWB can be plugged into the Control PWB, allowing connection of an external MODEM (via a socket on the front of the radio) and generation of sequential tones for revertive paging. No provision is made for the decoding of sequential tones. An RS232 interface (CCIT standard V24) is available, allowing connection of the radio’s external message bus to MODEMs, printers, personal computers etc is available and is detailed in a separate publication.