ed up. Others specify pager worn on body be used to replace the old one. The design of the programmer unit measurements in free field. While different antennas are affected in had to ensure that the current and time for breaking the links was different ways by the body, those favoured are those whose perfor- carefully controlled otherwise it was possible for the fused links to mance is enhanced by the body. Since different bodies affect the reform. The operator programmed the pager by means of a keypad same antenna to different degrees, in order to establish a claim for on the programmer unit. on body sensitivity, measurements of sensitivity of the same pager As personal computers became less expensive and more readily on 30-50 different people are required. However, there appears to available, field programmers for service work stations were de- be no obvious correlation between height or weight of the wearer signed using a simple driver interface between the PC and the pager and the sensitivity measured. It has been found that sensitivity memory. As EEPROMs became available these were used as the measurements made on various pager designs, each worn by 40 programmable pager memory. Early versions of 128 bits had suffi- people, can have standard deviations of approximately 4.0uV/m. cient memory for pagers with 2 addresses 31 bits long, and a series of programmable options. These were programmed by a PC control- 45.8.6 Power sources led device but needed 15 volts to satisfactorily programme the EEPROM. Later versions of the EEPROM with 4K of memory and To meet world wide markets the pager must be designed with easily 3 volts read/write capability superseded the earlier types and made available primary cells because, with the exception of on site sys- possible the storage of precoded alpha text, different language texts items with more than 20 to 40 pagers, the user generally does not and customised characters. These options are incorporated in the wish to purchase a charger. This considerably restricts the choice