# Connecting multiple DCMs and OA boards

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Question:
Question: Some remote ROADM sites require two or more DCM modules, which have significant attenuation. Two or more OA boards are needed. In this case, the connecting points of DCMs should be reasonable for the system to run normally.
Analysis:
Answer: The adjustable value is 11 dB. When DCMs F and A are connected to the TDC and RDC ports of the OAU board, the insertion loss between the two DCMs reaches 13.1 dB, resulting in insufficient OAU amplifying capability and low output optical power. The issue can be resolved by placing one DCM behind the OBU board, and the other between the TDC and RDC ports of the OAU board.
Root cause: When two or more DCMs are used, the attenuation should be considered, and the location of DCMs and OA boards should be arranged reasonably.
Solution:
None
Suggestion and conclusion:
None

###### Other related questions:
Functions and normal working ranges of bias current, cooling current, and back facet current of OA boards on BWS 1600G
The bias current of an OA board is actually the drive current of the laser on the OA board. A laser is actually a photodiode. Therefore, the drive current is also called bias current. Due to the differences between pump lasers, the bias current vary greatly even for lasers of the same type (for example, 100 mW 980 nm pump lasers). The bias current ranges for different pump lasers are as follows: 100 mW 980 nm pump lasers: < 250 mA 150 mW 980 nm pump lasers: < 350 mA 160 mW 1480 nm pump lasers: < 700 mA

Calculation of the total input optical power of an OA board
The total input optical power of an OA board can be calculated using the following formula: Total input optical power = Single-wavelength nominal input optical power + 10lgN (N: number of in-service wavelengths).

Method used to query the gain of an OA board
In the NE Explorer of the U2000, choose Configuration > WDM Interface. Then query or set the value of the Nominal Gain parameter.

Common OA boards of the OSN 6800
The common OA boards of the OSN 6800 are as follows: OAU1 (optical amplifying board) OBU1/OBU2 (optical booster board) CRPC (case-shape Raman pump amplifier board for C-band)

DCM/DCU connection on a line
If only OBU is configured on the line, connect the DCM/DCU between a variable optical attenuator and the OBU. If only OAU is configured on the line, connect the DCM/DCU between the TDC and RDC ports on the OAU. If both OAU and OBU are configured on the line, connect the DCM/DCU between the two OA boards.

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