Fracarro 270678, Руководство по эксплуатации

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16
ENGLISH
This guide should be used in order to obtain optimal
performance from your FRACARRO optical system.
STEP 1: calculating optical budget. Use the first diagram to calculate your optical bud-
get (optical loss between HTX and KRX). Add the correct number of dB corresponding
to the number of splits you’re applying, and add 0.4dB for each kilometer of fiber along
the trunk (or 0.25dB if you’re using a 1550nm transmitter). For example, if you have:
HTX – KSP1_2 – KSP1_4 – 8km of fiber – KRX, your optical budget will be: 7 + 3.5 +
0.4 x 8 = 13.8dB (
≈
14dB).
WARNING: unclean connectors may affect your optical budget!
Clean them care-
fully!
STEP 2: determining optimal input level.
The criti-
cal point is always the transmission of analog
terrestrial channels.
Let’s suppose we must tran-
smit 40 of them. If your head-end equipment allows
you to do this, then, set their power to the value
suggested by the table on the left (about 85dBµV,
referring to the 42ch row); otherwise, make sure
you aren’t exceeding it.
As a general rule, digital
transponders’ power must be 10dB-15dB lower
than analog channels:
for example, if you have
30 SAT transponders, their optimal setting is 70-
75dBµV per transponder.
STEP 3: calculating SNR and output level.
Considering an optical budget of 14dB, the
SNR can be read in the intersection of the
input level column and the optical budget
diagonal. In the previous example, the SNR
for analog channels results 51dB. Output
level can be read moving left until we cross
last column: in the example, it’s 82dBµV for
each analog channel.
For digital transponders, similar considera-
tions apply. If you set either DTT and SAT
transponders’ power 10dB lower than ana-
log terrestrial’s, output level will be 10dB lower as well, and SNR will be 10dB worst.
However, for digital signals 25dB of SNR is still a good value!
Further examples are reported in the user’s guide: we recommend to read them
carefully!