smitter and receiver frequencies. This is required SO that the base station can control the channels to be used. Batteries for phones are becoming increasingly important. All use packs of rechargeable cells. Very old ones might still use nickel cadmium (NiCad) packs, but many of the new handsets use nickel metal hydride (NiMH) or lithium ion (Li-ion) ones. The new cells can store more charge in a given volume or weight and can therefore last longer. However, they do need to be charged correctly as they are more easily damaged than their NiCad counterparts. New battery developments mean that new types of battery are appearing. The longer battery life is becoming increasingly important because the higher data content can result in increased battery drain and reduced battery life between charges. Comparing the earliest phones with those used today, enormous changes can be seen. Some of the first cellular phones required very large batteries by today's standards. These were required for three reasons. The first was that the integrated circuits used required relatively high levels of current compared to those available these days. Second, the large cell sizes of these early networks dictated that high power levels were needed, and this reflected in greater levels of current consumption. Finally, as already mentioned, battery technology has improved considerably. Base station The base station consists of a number of different elements. The first is the transceiver itself. This contains the electronics for communicating with the mobile handsets. Second, there is the antenna and the feeder to connect the antenna to the base station itself. These antennas are visible on top of masts and tall buildings enabling them to cover the required Cellular telecommunications 259 area. Finally, there is the interface between the base station and its controller further up the network. This consists of control logic and software as well as the cable link to the controller. The base stations are set up in a variety of places. In towns a