1. The problem description:
Frequency's interference of a microwave link
2. Problem scenario:
During the alignment of antennas, the Received Signal Level (RSL) for both sites only can be achieved at -40 dBm whilst the Expected RSL for the link as in Link Budget is -32dBm. After few hours of antenna's aligning, the RSL still at -40dBm and it does not go any further.
3. Problem impact:
Since the RSL is not achieved, the problem is disrupting the commissioning of the link and integration of the service.
4. Handling Process:
Frequency's interference means that there is an external frequency for other microwave link that is interferring with our microwave link. There two ways that can be performed to make sure the interference exists:
i. 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, RSL reading should be at -90dBm. But if there is a 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.
ii. Change the frequency to any frequencies in the same sub band and then monitor the RSL. If after using other frequency, the expected RSL suddenly can be achieved, this means that there is other microwave link nearby is using the same frequency with the original frequency.
5. Root Cause
There is two possibilities for the interference.
a. There is no proper frequency scanning performed before installation.
b. Even if a proper frequency scanning was performed and the frequency was confirmed not being used by other link, the other link probably was installed illegally before our link is installed.
6. Conclusion:
To avoid the problem repeated, always bring the frequency scanner to site during installation. This is to ensure that frequency is FREE.
