Microwave link frequency interference

Hello TX Experts,

We are having the following problem in our network when trying to align antenna:
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.

Since the RSL is not achieved, the problem is disrupting the commissioning of the link and integration of the service.

Do you have any suggestion?

Hello @Rafael_Caixeta.

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:

  1. 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.

  2. 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:

  1. There is no proper frequency scanning performed before installation.
  2. 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.

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Possible causes for a low RX can be diverse.

  • ODU/RAU incorrectly attached to the waveguide or the antenna bracket.

  • Depending on the vendor you should also check polarisation is correctly configured at the antenna, both sides of the link. I remember old Ericsson antennas have a plate on the back you need to adjust depending on the polarisation V/H.

  • BTW check the antenna is perfectly horizontal on both sides: if the link is not tight it might have angle which ‘alters’ the polarisation.

  • Software ATPC. When aligning a MW link ATPC has to be disabled and a fixed value set. Otherwise ATPC will alter your alignment.

I might be forgetting stuff, it’s been a while since my last MW installation.

@Rafael_Caixeta labelled the topic as interference but he states they get -40 when they should be getting -32.
I don’t think it’s an interference, because @marcelofb already said with the remote link RF off you should be around -90, and if there is an interference you have more RX so your RX would be stronger than the expected (for example -80 or -75 instead of -90 or -94).
I’m not sure I explained it correctly, but the fact is your RX is higher than expected in case of another link feeding yours.

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Salam
how to do interference test 2+0 XPIC link?