Adjacent Channel Interference for DVB-T at UHF Bands in the South of Mauritius for Summer Season

Abstract

Government decided to launch digital broadcasting as from October 2005. The implementation has been carried out at the national broadcasting carrier (MCML). Digital transmission is being done on channel 28 while analogue television (TV) is on channel 27. Adjacent channel interference occurs between analogue TV signal and Digital TV signal as the spacing between the signals is only 20 MHz. In this paper we present measurements made to determine the degradation caused by an analogue PAL television interference on digital television signal. The experiment was done at distances 5 km, 10 km and 15 km around the base station at various locations. At each site, measurements were made using a log-periodic antenna at heights of 4 m and 6 m above the ground. It is shown that most measuring sites selected satisfy the lower adjacent protection ratio recommended by ITU-R. However, in 12 sites the power ratio is lower than the recommended ITU-R value of -11 dB. Secondly, the results show that there is negligible effect on the channel interference at the predefined heights. The results for distances of 5 km, 10 km and 15 km prove that the power ratio due to the overlapping of the two spectra remains constant and does not depend upon distance from the base station. Finally, a test was carried by increasing the transmitted power from 200 W to 250 W. The test shows that there is no difference in the lower adjacent channel interference despite the fact that theoretically there should have been an improvement. Further investigation should be carried out to determine its cause.