 limitations by reviewing first the technologies used and secondly the spectrum into which those technologies are presently deployed. 16.4 DMR 446 This is a digital PMR standard developed through ETSI and called 446 as 446 MHz is where some license exempt spectrum has been made available in some countries, for example the It is neither intended nor suitable for multimedia transmission. DMR products are available from Motorola, Icom, Kenwood, Tait and Entel and could potentially be deployed into other UHF and particularly VHF PMR applications. As we shall see later there is a problem of scale economy with these products and their target markets. 16.5 TETRA and TETRA TEDS TETRA is originally a European standard for trunked radio based on 25 kHz channel spacing with a 4 slot frame structure. A more recent extension of the standard, TETRA Enhanced Data Service (TEDS) scales the 25 kHz channel spacing to 150 kHz and uses 16-level QAM to support up to 500 kbit/s as a 'close to cell' data rate. TETRA handsets are available from Motorola, Kenwood, Sepura and Selex. Nokia has not developed handsets for this market since 2005. Even assuming general availability of TEDS complaint handsets, present TETRA cell densities would mean these higher data rates could only be supported in limited geographic areas. This is not presently a major problem. Many specialist user communities are rightly hesitant about adopting new technologies or new variants of existing technologies. The sale of the TETRA Airwave network in the UK in 2007 for close to £2 billion pounds proves that good revenues and margins are available based on the provision of voice combined with relatively low data rate services. However, it is reasonable to expect that this will change over time particularly if the performance gap between TETRA radios and cellular handsets continues to widen, which it will for reasons that we explain later. Making Telecoms Work 16.6 TETRAPOL The 'other' European trunked radio standard introduced by Matra, now EADS, based on narrowband 