eputed to have united the Scandinavian people in the tenth century AD. The Bluetooth standard took its name from him because it endeavours to unite personal computing devices. Bluetooth is primarily a data system and can carry data at speeds up to 721 kbps, but it also offers up to three voice channels. The technology enables a user to replace cables between devices such as printers, fax machines, desktop computers and peripherals and a host of other digital devices. Furthermore, it can provide a connection between an ad hoc wireless network and existing wired data networks. The system is based round a frequency hopping carrier. This provides a greater dynamic range than if a direct sequence spread spectrum technique had been adopted. If direct sequence spread spectrum techniques were used then other close-by transmitters could block the required transmission if it is further away and weaker. The data is modulated onto the carrier using a form of frequency shift keying known as Gaussian frequency shift keying. The frequency shift keyed carrier is filtered to ensure the sidebands do not extend too far either side of the main carrier. By doing this it achieves a bandwidth of 1 MHz with stringent filter requirements to prevent interference on other channels. With a hopping transmission, the carrier only remains on a given frequency for a short time, and if any interference is present the data will be resent later, but on a different channel that is likely to be clear of other interfering signals. The standard uses a hopping rate of 1600 hops per second. These hops are spread over 79 fixed frequencies that are chosen in a pseudo-random sequence. The fixed frequencies occur at 2400 + n MHz where the value of n varies from 1 to 79. This gives frequencies of 2402, 2404 2480 MHz. In some countries the ISM band allocation does not allow the full range of frequencies to be used. In France, Japan and Spain, the hop sequence has to be restricted to only 23 frequencies. The transmitter powers for Bluetooth are usually low. Th