al hardware configuration is shown in Figure 61.21. The Depending on the system being considered, data signalling may individual instruments are controlled by a central microprocessor. take place on permanently allocated channels or on voice channels Further system components may be integrated with the test set as allocated from time to time as required. required. These can be controlled by an external computer via the For analogue cellular systems the signalling itself takes the form widely used IEEE bus. For example, users may wish to include a of a data message using typically fast frequency shift keying programmable power supply or a second signal generator for inter- (FFSK) or phase shift keying (PSK). Digital networks use methods ference response testing. Modgen Dupl. synth. Synth. Volt. Sinad dist. Demod Filter hp, Ip, r.m.s. CCITT count count count stor. scope milli-volt spectr. power spectr. analyz. Demod a.f. a.f. Mod r.f. r.f. 2.r.f. Probe ext -30dB (d.c.) Figure 61.21 Radiotelephone test set block diagram Digital cellular test equipment 61/23 61.7.2 Operation of the test set ards. A modern cellular radio test set is capable of storing test software for all of these standards plus Radiocom 2000 and C-NET. During the test of the mobile radio all signalling functions (gener- ation and analysis of data telegrams) are handled by the test set which must also make the r.f. and a.f. measurements. There are two Digital cellular test equipment main testing modes: With respect to test equipment and methods, the main differences Many mobile radios feature a service mode which may be between conventional mobile radio and the new digital radio net- accessed via the keyboard of the radio. For radios with special works (to which GSM belongs) can be categorised in the following test interfaces, the necessary control signals may be generated by the test set using either the RS232C interface or a general purpose I/O interface. In this mode the functions of the radio 1. The transmitted information is completely digitised