# Difference between M40V and M40

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Both M40 and M40V are optical multiplexer boards that multiplex a maximum of 40 single wavelengths into one multiplexed wavelength. Their main difference is that each optical port on the M40V board is equipped with a built-in electrical variable optical attenuator (EVOA) to adjust the input optical power of each channel.

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Whether OPA commissioning is supported for wavelengths added on the MRx, MRxV, M40, or M40V boards in the WSD9+RMU9 configuration
When the RMU9 board is used to add wavelengths, OPA commissioning is supported when OTU boards are directly connected or connected to the MRx, M40V, or MRxV boards. When the MRx or M40 board is connected, however, single-wavelength commissioning is not supported. This is because an EVOA is integrated into each add port of the RMU9 board but the RMU9 board cannot commission single wavelengths as WSS modules do. When the MRx or M40 board is connected, no single-wavelength commissioning point is available in the wavelength adding direction. Only multiplexing-wavelength commissioning is supported. When OTU boards are directly connected or the M40V board is connected, single-wavelength commissioning is supported at each EVOA.

Optical power difference between the IN port of the D40 board and the OUT/MON port of the M40 board
The MON port of M40 board has 10 dB lower optical power than the IN port of the D40 board and the OUT port of the M40V board. The split ratio between the MON port and OUT port and that between the MON port and IN port are both 10:90. In other words, the optical power of the MON port is 10 dB lower than that of the IN port. The calculation formula is as follows: Optical power (dBm) of the IN port �?Optical power (dBm) of the MON port = 10 x lg(90/10) = 10 dB.

Insertion loss of an M40V board
When the attenuation of the embedded VOA on an M40V board is set to 0 dB, the minimum insertion loss of the M40V board is 8 dB.

Adjacent channel isolation for the M40 board
For the M40 board, the adjacent channel isolation should be greater than 22 dB.

Differences between IN_PWR_LOW differ from IN_PWR_ABN
IN_PWR_ABN is the predecessor of IN_PWR_LOW/IN_PWR_HIGH. Due to historical reasons, both alarms exist in the OptiX OSN 8800.

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