he use of repeaters? The detector is a PIN type. Turn to Table 9.7 and determine that the threshold (dBm) for a BER of 1 X 10-9 is -46 dBm at 1.3 um. One EDFA is used with a gain of 40 dB. This now becomes the starting point for the link budget. The light source is a laser diode with a -0.3-dBm output. The receiver threshold is -46 dBm, leaving 45.7 dB in the power budget. Add to this value the EDFA gain of 40 dB, bringing the power budget up to 85.7 dB. We allocate this value as follows: Fiber at 0.25 dB/km Two connectors22 at 0.5 dB each or a total of 1.0 dB 22 These connectors are used at the output pigtail of the source and at the input pigtail to the detector. Connectors are used for rapid and easy disconnect/connect because, at times during the life of these active devices, they must be changed out for new ones having either failed or reached the end of their useful life. CONCEPTS IN TRANSMISSION TRANSPORT Fusion splices every kilometer; allows 0.25 dB per splice A margin of 4 dB If we subtract the 1 dB for the connectors and the 4-dB margin from the 85.7 dB, we are left with 80.7 dB. Add the splice loss and the kilometer fiber loss for 1-km reels, the result is 0.5 dB. Divide this value into 80.7 dB, and the maximum length is 160 km between a terminal and first repeater or between repeaters. Of course, there is one less splice than 1-km lengths, plus the 0.45 dB left over from the 80.7 dB. This will be additional margin. Setting these calculations up in tabular form as follows: Connector loss @ 0.5 dB/conn, 2 connectors 1.0 dB Margin 4.0 dB Splice losses @ 0.25 dB/splice, 160 splices 40.0 dB Fiber loss, 161-km fiber @ 0.25 dB/km 40.25 dB Total 85.25 dB Additional margin 0.45 dB For an analysis of dispersion and system bandwidth, consult Ref. 12. 9.5 COAXIAL CABLE TRANSMISSION SYSTEMS 9.5.1 Introduction The employment of coaxial cable in the telecommunication plant is now practically obso- lete with the following exceptions: The last mile or last 100 feet in the cable television (CATV) plant As an RF transm