5.Calculation of satellite operating down link EIRP
1. Saturated EIRP (dB W) It is the EIRP of the satellite, at which ground station amplifier goes in to saturation.
2. Operating flux density (dB /Sq m) The traveling tube amplifier in a Earth station transponder exhibits power output saturation. The flux density required in the receiving antenna to produce saturation of the TWTA is termed the saturation flux density.
3. Amplifier back off To reduce inter-modulation distortion, the operating point of the TWT must be shifted to the linear portion of the curve from nonlinear portion, the reduction in input power being referred as input back off. When multiple carriers present, the power around saturation, for any carrier, is somewhat less than the achieved with single carrier operation.
4. Input back-offThe input back-off is the difference in decibels between the carrier input at the operating point, and saturation input that would be required for single carrier operation.
5. Output back off Where in put back off is employed corresponding output back off must be allowed for the satellite EIRP.
6. Satellite operating downlink EIRP(dB W) Satellite operating down link EIRP can be calculated as follows
Satellite operating downlink EIRP(dB W)
= Satellite operating flux density + ((Saturated EIRP - Output back-off )-(Saturation flux density - Input back-off))......
Example : Calculate satellite operating downlink EIRP (dB W) for the satellite operating flux dencity-124.23 dB satellite EIRP 32 dB out put back off 6 dB saturation flux density -83 dB input back off 9 dB