User's Manual
Models CH45
EIA 422 or 485
3-1
3. APPLICATIONS
When planning a system using Model CH45 Link/Repeaters, the following considerations should be
reviewed:
• Data Rate
• Optical Budget and the distance between connected units
• Number of units in a loop configuration
• Powering the Link/Repeaters
• Type of communication including format
• Selection of Fiber Optic Cable (FOC)
3.1 DATA RATE
Model CH45 Link/Repeater automatically supports all data rates from 1000 bits per second to 2 Megabits
per second (with the data coupling jumpers in the factory default settings, or DC to 2 Megabits per second
with the data coupling jumpers set to the DC position, see Figure 4 and section 1.2.4). No internal
selection nor setting is required. However, it is necessary that all connected IEDs be set at the same
data rate.
3.2 OPTICAL BUDGET
The optical budget is a ratio of the receiver sensitivity to launched optical power, i.e. amount of light loss
available from the transmitter to the receiver. It is calculated on a log scale so that a 3 dB loss is equal to
half of the original power, 10 dB is one tenth of the original power, 20 dB is one hundredth, etc. Many
different elements in the optical circuit can induce losses (attenuation) to the power of the signal. This
attenuation must be taken into account when determining the distance that the signal can be transmitted.
The major factor is the attenuation of the fiber optic cable. Cable attenuation is expressed as "X" dB per
kilometer. Other factors of attenuation include FOC fittings (terminations, splitters, etc.) FOC diameter,
and FOC aging.
Optical budget is the result of the expression:
Launch Power [µw]
Each Model CH45 Link/Repeater has an available optical budget of 19 dB.
3.2.1 Cable Attenuation Factors
The following cable factors must be applied as corrections to the optical budget.
3.2.1.1 Diameter
Multi-mode:
FOC of different diameters will vary the available optical budget of a system due to
different FOC core diameters. The 19 dB optical budget is applicable to 62.5 µm
diameter FOC. Table 1 shows the correction factors to use on the available optical
budget for different diameter cable.
Table 1
FOC DIAMETER FACTOR
50 µm
-3 dB
100 µm
+4 dB
200 µm
+7 dB