Satellite due to rain fading at Klong downlink availability of Thaicom 3 Yai ground station

This article reports the study of rain rates and rain attenuation on satellite signal at Klong Yai district, Trad province. This area has heaviest rainfall in the country, more than 4000 mm/year. We measured the downlink signal of the Thaicom 3 satellite at 12.271 GHz horizontal polarization. The period of recorded data are from January to December 1998. We analyzed data in the form of percentage of time in one year both rain rate and rain attenuation. Those values always use for link margin calculation of R_0.3, R_0.1, R_0.05, R_0.03, R_0.01 are 42, 84, 120, 162 and 222 mm/hr, respectively. Rain attenuation of A_0.3, A _0.1, A_0.05 are 8.9, 15.5 and 20.1 dB respectively. The worst month are August and September. These values which are higher than the ITU-R rain zone P, Global rain zone H at 0.01% of time are 75 mm/hr and 10 mm/hr. As for attenuation, our measurement values are higher than the ITU-R rec. 618-3 about 1 dB at 0.05% of time. We approximate the downlink rain fall availability of the signal by calculating C/N from general link design equations