Huawei RTN 950 MW equipments are installed as XPIC configuration. Under AM function the modulation of one radio link who works at V-direction always changes between 128QAM and 256QAM.
AM_Downshift alarm appears periodically.
Step1: Mute the H-direction and check the modulation on V-direction.
Step2: Perform some tests based on exchanging of hardware parts in the system
Step3: Mute all the ODUs on these two links and query the receive signal
There are few possible reasons:
1. ODU is faulty.
2. Waveguides or IF cables have some problems.
3. There is some interfierence in the working frequency channel.
After performing steps 1 to 3 the conclusion is that all the Hardware elements in the system are OK, the interfierence is not caused by the other polarization. The
problem was discovered when we perform step 3.
When query the RSL when all ODU were mute, there was -84dBm level while it should be -90dBm. This means there is interfierence in this channel.
The suggestion is to change the channel or find the source of this interfierence.