airFiber - Troubleshooting Signal and Link Issues


Overview


This article covers the most common issues affecting weak or fluctuating signal levels between wireless devices. If you have a weak or fluctuating signal, this can also affect your link stability and total throughput. If you are seeing link disconnections or low throughput, please read through this article.


Table of Contents


  1. Line of Sight
  2. Interference
  3. Physical Alignment
  4. Inversion
  5. Related Articles

Line of Sight


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  • If the line of sight between the two devices is not clear, signal levels will be weak and unstable.
  • Fresnel Zone requires at least 60% clearance for stable signal levels.
  • Mounting devices higher can improve line of sight and Fresnel Zone clearance.

Interference


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  • Use airView from both sides of the link to find a clear channel.
  • Use a narrower Channel Width to reduce the effect of interference in noisy environments and improve link stability.
  • Avoid Auto Channel selection without creating a Frequency List based on airView results.

 

Physical Alignment


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  • Ensure that the devices are correctly aligned according to the radiation pattern found in their respective data sheets. Datasheets and quick start guides can be found at the bottom of each product's page when navigating from here: https://www.ubnt.com/products/ or in our Downloads section.
  • Ensure that the devices are tightly secured after verifying alignment so they do not twist on the mount.
  • Ensure that the mount is tightly secured.

Inversion


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On long links, generally greater than 15 kilometers, it's possible to experience an effect known as atmospheric inversion or temperature inversion. This is caused by the RF passing through a layer of air that is warmer or cooler than the air above and below, causing the air to have a different density than the surrounding air, which causes the RF path to bend and no longer be a straight line. Since the RF path is no longer straight, your signal will become unstable until this atmospheric event passes.

In most cases, this will be noticeable during specific time frames each day and will always go back to normal after some time. Generally, you will see this effect during the late evening or early morning hours when the sun is rising or setting. But can happen at any point during the day or night when the ground temperature is vastly different than the air temperature. This occurrence is exacerbated in links that pass over bodies of water due to the massive temperature difference between the water and the air directly above it.

There are only a few ways to overcome this issue.

  • Set up a failover link that follows a new path.
  • Shorten your link by adding a hop in the middle. Shorter links do not have to cover as much distance, so there is a greater chance of avoiding inversion events by using multiple hops.
  • Raising the antennas can get your RF path above the inversion event. The higher the RF path, the less noticeable the inversion is.

Related Articles


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airFiber-Best Location for a High-Performance Link

airMAX - Using airView to Find the Best Channel

airMAX - Selecting the Best Channel Width


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