 # Link Loss  What is Link Loss? P t (transmitted power) – P r (received power) P t (transmitted power) – P r (received power)  Why calculating link loss?

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Link Loss  What is Link Loss? P t (transmitted power) – P r (received power) P t (transmitted power) – P r (received power)  Why calculating link loss? Determine required satellite output power for different operating frequencies. Determine required satellite output power for different operating frequencies. Design and spec of satellite power amplifier Design and spec of satellite power amplifier

R GrGr GtGt PrPr UH PtPt Link Loss = P t - P r

Estimated Link Loss Estimated Link Loss Assumptions:  Free Space Speed of light = 3 x 10 8 m/s Speed of light = 3 x 10 8 m/s  Low Earth Orbit (300 ~ 800 km) R = 700 km R = 700 km  Antenna Satellite: Half Dipole antenna (Tokyo University) Satellite: Half Dipole antenna (Tokyo University) G t = 2.2 dB = 1.66 Ground Station: Crossed Yagi antenna (T.I.Tech.), G r ~ 14 dB = 25.12 Ground Station: Crossed Yagi antenna (T.I.Tech.), G r ~ 14 dB = 25.12

Estimated Link Loss (Cont.)  P r ≈ -120 dBm = 1 x 10 -12 mW  Negligible atmospheric attenuation for low frequency (f < 10 GHz) Higher Altitude → Lower Attenuation Higher Altitude → Lower Attenuation High Altitude

R = 700 km G r = 14 dB G t = 2.2 dB P r = -120 dBm UH P r = P t G r G t λ 2 / (2πR) 2 Friis Equation: PtPt

Link Loss Calculation 144 MHz 400 MHz 1 GHz 5 GHz 10 GHz 20 GHz

Other Non-ideal Factors  Fading  Ground Reflection  Multi-path Constructive or Destructive Interference Constructive or Destructive Interference

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