1
Fiber Optic
Series
1
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PICO MACOM
Fiber Optic
Series
Chapter 4
Input Level versus Channel Loading
The PFT Transmitters are designed to properly modulate the light output with a specified number of 6
MHz. channels. The PFT-x Specifications shows unit operation with 78 NTSC channels at 15 dBmV
input level each, plus 300 MHz of QAM channels at –6 dB (9 dBmV) input level. If the number of
higher level NTSC signals is reduced, the input levels may be increased to provide the same laser drive
level and end-to-end performance.
The formula to use is: Desired Input Level =
Specified Input Level –10Log (actual channel count /specified channels)
Table of Input Level vs. Channel Count
channels
actually
input
Delta
Input
level
channels
actually
input
Delta
Input
level
channels
actually
input
Delta
Input
level
channels
actually
input
Delta
Input
level
1
18.92 33.92
21
5.70 20.70
41
2.79 17.79
61
1.07 16.07
2
15.91 30.91
22
5.50 20.50
42
2.69 17.69
62
1.00 16.00
3
14.15 29.15
23
5.30 20.30
43
2.59 17.59
63
0.93 15.93
4
12.90 27.90
24
5.12 20.12
44
2.49 17.49
64
0.86 15.86
5
11.93 26.93
25
4.94 19.94
45
2.39 17.39
65
0.79 15.79
6
11.14 26.14
26
4.77 19.77
46
2.29 17.29
66
0.73 15.73
7
10.47 25.47
27
4.61 19.61
47
2.20 17.20
67
0.66 15.66
8
9.89
24.89
28
4.45 19.45
48
2.11 17.11
68
0.60 15.60
9
9.38
24.38
29
4.30 19.30
49
2.02 17.02
69
0.53 15.53
10
8.92
23.92
30
4.15 19.15
50
1.93 16.93
70
0.47 15.47
11
8.51
23.51
31
4.01 19.01
51
1.85 16.85
71
0.41 15.41
12
8.13
23.13
32
3.87 18.87
52
1.76 16.76
72
0.35 15.35
13
7.78
22.78
33
3.74 18.74
53
1.68 16.68
73
0.29 15.29
14
7.46
22.46
34
3.61 18.61
54
1.60 16.60
74
0.23 15.23
15
7.16
22.16
35
3.48 18.48
55
1.52 16.52
75
0.17 15.17
16
6.88
21.88
36
3.36 18.36
56
1.44 16.44
76
0.11 15.11
17
6.62
21.62
37
3.24 18.24
57
1.36 16.36
77
0.06 15.06
18
6.37
21.37
38
3.12 18.12
58
1.29 16.29
78
0.00 15.00
19
6.13
21.13
39
3.01 18.01
59
1.21 16.21
79
-0.06 14.94
20
5.91
20.91
40
2.90 17.90
60
1.14 16.14
80
-0.11 14.89
