Televes 8674, User Manual, Page: 29 / 36

29
User manual Optical Transmitter
ENGLISH
Note 9: Maximum optical losses supported by the link
The maximum value of the optical losses supported by the optical fiber link is that when the minimum input level and the maximum input
level are the same.
The maximum input level depends on the number and type of the channels to be distributed.
The minimum input level depends on the optical losses and the required C/N of the channels to be transmitted.
Generally, the worst case is when analogue TV signals are transmitted in TV band, as these are the ones that require the highest C/N.
Example 1.- Transsmision of 20 analogue TV channels
V
in
maximum ( see Note 2 ) = 106 dBµV – 10 log (20 – 1) = 96 dBµV / channel
To have V
in
min = V
in
maximum = 96 dBµV, optical losses must be 16.5 dB ( see Note 8 )
These losses are equivalent to either a 30 Km link with two optical connectors and no optical splitter, or a 4-way optical splitter and a
14 Km link with its optical connectors.
Example 2.- Transmission of 40 analogue TV channles in TV band and a complete transponder of digital channels in SAT band
V
in
maximum ( see Note 3 ) = 88 dBµV / channel for analogue TV channels
78 dBµV / channel for digital satellite TV
To have V
in
min = V
in
maximum = 88 dBµV, optical losses must be 12.5 dB ( see Note 8 ).
For this value of optical losses the minimum input level for digital channels is 64 dB, value that is much lower than the minimum input level
for analogue channels.
These losses are equivalent to either a 23 Km link with two optical connectors and no optical splitter, or a 4-way optical splitter and a 6 Km
link with its optical connectors.