hen the deflection angle is less than 50° or where no site exists from which one reflector could see both terminal stations; this is usually the case when transmitting over a mountain ridge. This problem can be solved by using two parabolic antennas placed back to back. Transmission Network Planning and Optimisation Table 3.11 Parameter values for error performance calculations Parameters Site A Site B Radio frequency 7.4 GHz vertical Hop length 15.0 km Latitude Longitude 80° E Percentage pL 50.0 % Geoclimatic factor 1.41E-003 Rain rate (0.01 %) 120.0 mm/h Station heights 200.0 m 200.0 m (reference levels) Antenna heights 50.0 m 50.0 m (above station reference levels) Feeder lengths 60.0 m 60.0 m Feeder loss/100 m 4.9 dB 4.9 dB Feeder type EW 64 EW 64 Antenna diameters 1.2 m 1.2 m TX output power Ptx 27.0 dBm Free space loss (FSL) 133.4 dB Additional terrain loss Lad 0.0 dB Antenna branching loss Lbr 5.0 dB (SD, HSB)a Feeder losses L1 3.4 dB Connectors loss Lc2 3.4 dB Antenna gains G1 36.8 dBi 36.8 dBi Hop loss in nonfaded state Lho 71.7 dB Received unfaded power Prx -44.7 dBm Receiver threshold power Prxth -76.5 dBm at BER 10-3 Flat fading margin (FM) 31.8 dB Calculated flat outage time Pfm 0.0051 % Total outage time p (nondiversity) 0.0051 % Annual unavailability due to rain 0.0001 % Flat outage with diversity Pfmd 0.0001 % "SD, space diversity; HSB, hot standby. Microwave power is received from one antenna through a short piece of transmission line and re-radiated. Since these parabolic antennas may be pointed individually to the transmitting and receiving antennas, the projection factor is unity. The gain of the repeater with back-to-back antennas is GR=GAIGA2-A (3.40) where GAL GA2 = gains of the two antennas A = coupling loss Microwave Propagation The expression for the total free space loss with two parabolic reflectors is given by Lo = 184.88 + log (did2) + 40 log fGHz - Grl Lcr (3.41) The total free space loss in a two hops transmission with a single passive repeater is = 141.98+201og(djd2)-20log AR (3.4