Transient Measurements on GSM/PCN Synthesizers
The GSM mobile phone system is the first civil radio network using purely digital transmission methods. In addition to the modulation mode GMSK (Gaussian Minimum Shift Keying) itself, both a time and a frequency multiplex method are used. This means for instance that the bits to be transmitted are distributed to several socalled bursts (time multiplex). These bursts are then in turn transmitted at different frequencies in the frequency hopping mode. Due to the frequency hopping mode, the timing used in GSM/PCN networks and the low phase error required for correct data transmission, stringent requirements regarding the frequency transient response are placed on the synthesizers used in the base and mobile stations. For a frequency error of <100 Hz the transient response must be within approx. 100 us to keep the residual phase error caused by the synthesizer sufficiently small. The Modulation Analyzer FMA/FMB with its high-precision AM and FM demodulators featuring DC coupling capability is particularly suitable for an uncomplicated measurement of transient responses in conjunction with an oscilloscope. Both the FMA with its low residual FM in the GSM band from 890 to 960 MHz and the FMB, which in addition also covers the PCN band from 1710 to 1880 MHz, provide in conjunction with the fast transient response of the FM demodulator the characteristics required. Highest precision regarding the transient response is provided by the FMA/FMB's special function 'IF 300 kHz'.
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