Aligning antennas

A step by step tutorial with recommendations to align antennas of a LibreRouter device with LimeApp1.4

Ensuring the best allignment possible in a wifi link is vital for the proper functioning of the community network and its performance.

It is strongly recommended to position the antennas as well as possible; even if the feeling of usability of the network conforms to those who use it.Accumulating links of insufficient quality results in a network with problems that are difficult to diagnose or in unreliable diagnostics.

It is a low complexity task that requires dedication, patience, and time.

Table of contet:

🙌 Recommendations before starting

To be able workingcorrectly, it is necessary to verify some of the following preconditions and necessary materials:

• Check weather conditions in advance. Do not work on days with wind, drizzle, or extreme temperatures.
• Prepare the appropriate clothing, footwear, and safety elements, especially for work at heights.
• Check the correct installation of the node and its fastening structure.
  • Check that everything is firm, without pendular or rotational movement,and the equipment is firmly fastened to the pipe. Consider the checklist as support.
  • Whenever you are at the node´s height, take the opportunity to look at the integrity ofall its parts: connectors well connected, healthy cables and boxes, LEDs on, etc. Consider that the task becomes much more complex when the antennas are not in place within easy reach. Whenever possible, place the antennas within reach and good locations where work can be comfortable even if it is not the highest point.
• Place the antennas slightly loose but tight enough to avoid movement while not being held on the hand. It allows us to move them during the alignment process.
• Confirm clear line of sight. The electromagnetic waves from wifi link underminds when passing through objects, trees, and other obstacles. For this reason, it is vital to verify that there is a clear line of sight between the two mounting points assembly. The Participatory Mapping of a Free and Community Network material may be useful.
• Analyze the possible link with a map. It is recommended to view a satellite map in advance, mark the line, and mark as a reference something near the alignment so that it can be simply identified.
  
• Analyze the elevation profile of the terrain and assess the feasibility of the link. In this profile, it is important to take into account the exact location of both antennas, the line of sight between both nodes, the curvature of the Earth, and the Fresnel zone. There are link calculators that cross-reference this data automatically. It only requires a little information about their use. For example, two free options are: airLink y LigoWave.
  

✅ Verify that the LibreRouter devices are linked

• If the LibreRouter nodes are about to be mounted: it is advisable to turn them on beforehand to corroborate that they are working and linking well. Trying to align in the distance with already mounted antennas that do not work can be very frustrating.
• If the LibreRouter nodes are already mounted: Check that the LibreRouter nodes are on, and that LimeApp can be accessed from both.

⚠ If the LibreRouter Team fails to see any signal or if it fails to see the signal of the node you want to target,i.e. it does not link to the target node:

• LimeApp will give notice of the situation with a display that says «This radio is not linked to other nodes».
• If you are aligning Antenna 1 (Radio1), verify that you are pointing to Antenna 1 of the other node. The same situation occurs if it is with Antenna 2 (Radio2). That is, it is possible to align 1 with 1 and 2 with 2 without crisscrossing.

• Try to perform a first alignment «by eye» until you have a link, even if the signal is poor.
• If the time has passed and a link couldn’t be reached, check again that both devices are on and accessing the LimeApp. If it persists, re-evaluate the line of sight, check the integrity of the node parts, and test the dismounted equipment at close range.

🎯 Let’sAlign!

Usethe Alignment tool in LimeApp 1.4

All the detailed information about this tool is in the Alignment material. Don’t forget to review it! 🤓

1. Access the LimeApp of the base node from where you are working.
2. From the Menu, go to the Alignment screen.
3. Choose the node against which you will align and enter the specific and detailed information.

The objective is to reach a value that is as close as possible to 0(zero) This value represents the link quality measured in decibel milliwatts (dBm). It always corresponds to a negative number, so -65 indicates a better signal than -72.

LimeApp assigns the colors green, yellow and red to identify when a link signal is good medium or poor quality.

✔ Consider as valid the best value that has been repeated several times.
✘ Discard isolated values that represent an important jump in the measurement, no matter how good they may seem,as they are not representative.
🟡 If the best value you get is a link of average quality, it can be decided that this link is necessary for the community network, even if the signal value cannot be improved.
🔴 Poor quality links provide an awful user experience, wear and tear of social management and, it is advisable not to accept them.

Let’s do it!

The key is to move the antenna slowly and millimetrically, paying attention to the change in signal value that appears on the screen.

1. Move the desired antenna horizontally ↔ to the best value to obtain the best value.
2. Perform the same action in the vertical directionuntil ↕ obtaining better or equal to the value registered during the horizontal movement.
3. Finally, repeat the procedure in the horizontal direction, stopping the movement when reaching the best value or better.
4. Once the best alignment is achieved:
   • Fasten the antenna to the pipe or structure, tightly so that it does not move in the wind.
   • Make sure that the previously achieved value is not modified. It is usual that when adjusting, small movements are provoked that worsen the result.
   • Correct these variations as you adjust, slowly and patiently.
5. Perform the same task with the LibreRouter device(s) on the other side.

📌 To keep in mind:

Long links

On long links, the alignment is more sensitive to movement because the illumination angle is more open.

Illuminate a zone

In a mesh network, it is sometimes decided to target or illuminate a zone or several nodes simultaneously, instead of several nodes, instead of a single specific node. In this case, the most central node in the zone of interest, and check that the signal level is acceptable at each node to be linked.
Remember that all intervening nodes must use the same radio antenna.

For example, in this image, a coverage angle is depicted that seeks to cover nodes 1, 2 and 3 with a reasonable link quality for each one:

• Node 2 is the one with the best link quality, being at the center of focus.
• Nodes 1 and 3 have a lower but still acceptable link quality, since the aperture angle of the sectorial antennas of the LibreRouter allows it.
• Other more distant points, which are linked with low quality, should be avoided, as this is detrimental to the overall network performance, such as node 4.