Frequency interference means that there is an external frequency for other microwave links that is interfering with our microwave link.
There two ways that can be performed to make sure the interference exists:
Switch off the ODU at Site A and then monitor the RSL at site B. And then do the opposite. Switch off the ODU at Site B and then monitor RSL at Site A. If there is no frequency interference for the link, the RSL reading should be at -90dBm. But if there is an RSL reading in any value, meaning that the ODU is picking up the RSL from an existing microwave link that is using the same frequency. The link is having frequency interference.
Change the frequency to any frequencies in the same sub-band and then monitor the RSL. If after using another frequency, the expected RSL suddenly can be achieved, this means that there is another microwave link nearby is using the same frequency with the original frequency.
As for the root Cause, there are two possibilities for the interference:
- There is no proper frequency scanning performed before installation.
- Even if a proper frequency scanning was performed and the frequency was confirmed not being used by other links, the other link probably was installed illegally before our link is installed.
So, to avoid the problem repeated, always bring the frequency scanner to the site during installation. This is to ensure that frequency is FREE.