Power and Modulation Measurements on VHF Transmitters Example: Rohde & Schwarz VHF-FM Transmitter SU115

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.