Location and Aiming of External LTE Antennas

The directional antennas we use are a Yagi antenna. Because LTE is a MIMO signal, you need to have two antennas and your speeds will be best when the polarization isolates the two antennas as much as possible. The two LTE signals sent from the tower form an X shape. So you want to orient the two antennas to match that shape.

Polarization Diagram

This is the view of correctly polarized Yagi antennas as if you are looking toward the antennas from the cell tower. Yagi antennas pull signal down the long axis of the antenna, so you will want to mostly point the two antennas at the tower that you are trying to pull in, the antennas should be mounted fairly high up, and pointing horizontally toward the correct tower.

Aim diagram

If you have multiple, bonded, LTE modems, you generally want to start by aiming them at the nearest tower that matches the provider that the SIM card for each modem uses. Because of obstructions and reflections, you will likely need to aim the antenna after getting it generally oriented. This map is a very good starting point for figuring out what tower you are shooting for:

Canadian Cell Towers

If you have more than one LTE modem from the same provider and can see two towers from that provider, by all means you can try to hit both towers. That way you are less likely to saturate one tower's capacity. If one of the towers does hit saturation, you might still get decent bandwidth down the other leg.

The information about frequencies in use came from here: https://www.androidcentral.com/everything-you-need-know-about-4g-lte-canada Summary:

Carrier F1 F2 F3 F4
Bell 700 2600 1900 850
Telus 700 2600 1900 850
Rogers 700 2600    
SaskTel 700      

So... if you're getting 700Mhz signal, you likely have an LTE tower, if you are also seeing 2.6Ghz, it is probably not SaskTel. If you pick up 1.9Ghz and 850Mhz, you have a Bell/Telus (they share them) tower. Handy, huh? Well it would be, if you had an easy way to see what signal strength you are getting on different towers. Luckily: You should have access to a Spectrum Analyzer.

The device looks like this: rfexplorer.jpg

Here's a quick view of the screen with an antenna hooked to the RF-Explorer unit we have: -89dBm signal

The same setup in a nearby location with stronger signal shows that I'm pulling -79dBm instead of the -89dBm I was getting earlier, but at some point as I was walking around I had a stronger signal still. -79dBm signal

These numbers are an indicator of the number of Watts of power I'm getting from the incoming signal. -89dBM is the same as saying that the antenna is getting 1.26×10-12 Watts of power. -79dBm is equal to 1.26×10-11 Watts, or ten times as much power as the previous reading.

0 dBm would mean that you are getting 0.001 Watts (1 mW) of power. Really good speeds require between -60dBm and -80dBm. If you can get better that's fine, but you won't see much speed increase over a -60dBm signal. If you are not getting at least -80dBM, the LTE modem will use lower speeds to try to maintain the connection past other noise.

If you hit the menu button you can use the left and right arrows to page through the menus. The settings I'm using to find a good spot look like this:

Attenuation Menu Config Menu

The "Max Hold" setting causes the display to draw an outline above the most powerful readings you've seen so far. I switch between that and the "Normal" calculator that just shows current readings. Setting a reasonable Top and Bottom makes it easier to see small differences in signal strength. Setting the Marker to "Manual" lets you use the right and left arrows to select the frequency that you are interested in. It defaults to "Peak" which is annoying if you know exactly what you are trying to measure. Frequency Menu

Based on the frequency table given: If I were shooting for a Bell or Telus tower, I'd look for a frequency span of about 40Mhz, centered on 1900Mhz. For Rogers, 2600Mhz, and for SaskTel, 700Mhz.

For 700Mhz, you need the telescoping antenna and the (left) connector. For the higher frequencies, you want to use the little antenna and the 15-2700MHz (right) SMA connector.

Once you locate a good area to install your antennas, you should firmly anchor the poles, and attach the antennas to them so they won't drift around. Now connect a cable from the antenna (lightly torque the SMA connectors onto the unit, they need to be better than finger tight or your losses at the connector will prevent good readings) to the selected connector on the spectrum analyzer, and use it to find the best signal. Secure it to the pole, and then switch out the antenna on the RF explorer and repeat the process.

At this point, you should be able to hook up both of the antennas to the LTE modem and run a speed test. Try http://www.speedtest.net or using our iperf server at iperf.itel.com. Examples of speeds I got at different signal strengths looked like this. (All of these were shot at similar times of day, and using the same LTE modem and tower.)

Signal Download Upload Ping
-121 dBm 0.84 Mbit/s 0.14 Mbit/s 325.491 ms
-85 dBm 7.43Mbit/s 2.77 Mbit/s 143.672 ms
-55 dBm 9.53 Mbit/s 2.88 Mbit/s 62.658 ms

In the location where I did these tests, tower saturation played a bigger role than the signal strength though. I can see three towers from two providers. With this same LTE modem, indoors, on the stock antennas, I get about 2 Mbit/s during peak hours and can consistently hit 65 Mbit/s at night when nobody is on these towers.

If you're bonding multiple LTE connections, bolt down another pole (you might have to find a different location if you're shooting for a different tower) and repeat the aiming steps. Once all of your antennas are aimed, you need to run the cables inside, and attach the LTE modems to the appropriate antennas. Remember: The SIM card and firmware on the LTE need to match the towers that you are aiming for, so you might need to keep track of which cables go to which tower. As long as you use a matched pair of antennas, it does not matter which one is on the left or right connector of the LTE modem. Don't forget to lightly torque the SMA connectors, they need to be firm or you will not get good signal. There is no particular need for the LTE modems to be in the same place, but they are not rated to run outside in the weather, so the cables need to run into a shelter of some sort. Once the LTE modems are set up, you can route normal ethernet cable from them to wherever you have set up your bonder and hook them up there.

Omni directional, external antennas

We have a second type of external antenna. It is an omni-directional unit, so you don't have to aim it. In theory, it is not as good at picking out distant signals or rejecting noise as the Yagi, but the ability to place it up high, far from the LTE modem might still provide some improved bandwidth.

The omni-directional antenna are polarized from corner to corner: Omni Polarization Diagram

They should be oriented on the pole as shown by the red lines in this diagram. Omni Aiming Diagram

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