Televes 8674, User Manual, Page: 31 / 36

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User manual Optical Transmitter
ENGLISH
Note 11: Minimum input level to the link
The noise in the return path is lower than noise in the direct path. For example, for 10 dB of optical losses, the input noise level for a
analogue TV signal (Bw = 5 MHz) will be
-149 dBm/Hz –10 dB + (2 x 10 dB) + 10 log (5 exp 6)= -72 dBm = 37 dBµV
against 38.5 dBµV for direct path ( see table in Note 7 )
The minimum input level for ths same signal with a requested C/N of 46 dB will be 83 dBµV against 84.5 dBµV for direct path.
Furthermore, the requested C/N for the return path will be, in most cases, lower than the direct path.
As a conclusion, the limit of the link concerning the maximum optical losses that can be supported comes always from the direct path.