3 Results
A whole series of measurements has to be carried out for drafting an acceptance test report for a VHF sound broadcasting transmitter in compliance with ARD Specifications 5/3.1 (= TL 5820-3018 of the Deutsche Bundespost). As in most cases parameters like transmitter output power, frequency stability, spurious modulation, etc. have to be measured in the two stereo channels of the transmitter separately and at different modulation frequencies and frequency deviation, manual-controlled measurements are very time-consuming. In addition, a great variety of test equipment eg AF generator, stereodecoder, level meter, etc. is required for the measurements. FMAB with option FMA-B4 (AM/FM Calibrator / AF Generator) is ideally suitable for these measurements on VHF sound broadcasting receivers. The internal AF generator provides the signals required for the left and the right stereo channel. The MPX signal from the VHF transmitter is decoded by the built-in stereodecoder. As a result many of the tests and measurements required for the acceptance of VHF sound broadcasting receivers can be carried out without any additional test equipment being required. To give an example, a test program running under the graphics user interface Microsoft Windows has been developed for carrying out automatic power and modulation measurements via a PC.
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'.
Modulation Analyzers FMA (up to 1.36 GHz) and FMB (up to 5 GHz) are high-grade FM demodulators from Rohde & Schwarz with highly stable synthesizer, low-noise FM demodulator, automatic frequency tuning and fine-tuning, separation of AM from FM,all of which make Analyzers FMA/FMB ideal for phase noise measurements.