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ENGLISH
Measure the Fracarro OPT optical link with (audio/video digital programs only)
The measure of the Fracarro optical link can be done in three simple steps:
Step 1 – know the number of digital channels at the input and the optical attenuation of the link.
The first step is to know the number of digital channels that you want to transmit in the optical link. The number of chan-
nels to be considered for correctly measuring the optical link is the result of the addition of satellite transponders and
DTT bouquets. The number of SAT transponders can be fixed to 3 (the maximum number of transponders that can
be transmitted in a unique polarization). Therefore, to transmit 0 digital terrestrial channels, the total number of chan-
nels to be considered is given by (3CH SAT + 0 CH DTT) = 5CH. Furthermore, even the link’s optical loss from
the transmitter to the receiver should be considered (consider the worst case). For example, if you are using a -way
optical splitter (-3. dB optical) and 5 km of fibre optics ((-0.4×5)= - dB optical), the optical attenuation will be 3. +
= 5.dB (consider the possible losses of fibre connectorization).
Step 2 – determining the input signal level
The signal level that must be set at the transmitter input should be chosen according to the number of channels that
will be transmitted. If the number of channels that will be transmitted is 5 (3CH SAT + 0CH DTT), the input level
that will be set is 98dBµV. Example:
62
17.6 18.0 18.4 18.6
60
16.0 16.4 16.6
58
14.4 14.6
56
12.6
94
96
98 100 102 104 106 108 110 112 Pin (dBuV )
126 80
50
32
20
13
8
5
3
2 Channels
2
1
Level of the input signal
to the transmitter
Number of channels to
transmit at the input
Step 3 – calculation of CNR and output value
If you have to transmit 5 channels with an optical attenuation of 15dB, the input level of each channel (satellite or ter-
restrial digital) should be 98 dBµV (Pin). Table gives the CNR ratio of the digital satellite signals and table 3 gives the
CNR ratio of the terrestrial satellite signals. CNR will be about 1.6 dB in the event of satellite channels and 30. dB in
the event of digital terrestrial signals. The output level of the optical receiver will be 66 dBµV (in both cases).
82
28.4 29.7 31.0 32.1 33.2 34.1 35.0 35.8 36.5 37.1
15
80
27.7 29.0 30.1 31.2 32.1 33.0 33.8 34.5 35.1 35.6
16
78
27.0 28.1 29.2 30.1 31.0 31.8 32.5 33.1 33.6 34.0
17
76
26.1 27.2 28.1 29.0 29.8 30.5 31.1 31.6 32.0 32.4
18
74
25.2 26.1 27.0 27.8 28.5 29.1 29.6 30.0 30.4 30.6
72
24.1 25.0 25.8 26.5 27.1 27.6 28.0 28.4 28.6
70
23.0 23.8 24.5 25.1 25.6 26.0 26.4 26.6
68
21.8 22.5 23.1 23.6 24.0 24.4 24.6
66
20.5 21.1 21.6 22.0 22.4 22.6
64
19.1 19.6 20.0 20.4 20.6
62
17.6 18.0 18.4 18.6
60
16.0 16.4 16.6
58
14.4 14.6
56
12.6
94
96
98 100 102 104 106 108 110 112 Pin (dBuV )
126 80
50
32
20
13
8
5
3
2 Channels
Input channels: 5
TX input level: 98dBµV
CNR level: 1,6
Output level of the
receiver: 66dBµV
Figure 3 – Exemple of CNR reading
