Pointing Directional Antennas – what to look for

It is well known that using a directional antenna in a fixed location is the best way to increase signal when having subpar results.
However, signal strength alone does not guarantee great performance. There are other factors that can be detrimental and have a major effect on the speed and latency of your mobile broadband connection.

Assuming you have located the tower, purchased and installed the antenna, and are ready to point it, there is data you should be looking at while doing so – the Field Test screen. Ctrl-D password diagvzw for Verizon Access Manager, Ctrl-D password diagsmsi for Alltel Quicklink Mobile, ##debug# for Sprint Connection Manager, ##debug for Franklin Connection Manager … Select Field Test for all of these. Now look at this Verizon example:

VZ field test

I have the modem locked in HDR (EVDO only) mode and have scrolled down to the bottom set of numbers. The top set relates to voice/conversation and is of no use with the data modem. It is a good idea to be running a ping test in the background that won’t time out.
Take a look at what I have circled. These are the parameters you should look at when pointing the antenna. Starting from the top:

Ec/Io is maybe the most important field of all. This is a ratio of good to bad energy, representing the cell towers “cleanness” in its signal to you. Or simply put - signal to noise ratio. A perfect Ec/Io is zero. Once you start getting above –4dB your connection is going to suffer. What causes a high value? Several things such as trees, hills, buildings, walls, poor cabling, shorted connectors, inaccurate pointing, wrong antenna polarization, congested tower, and multipath.
HDR RSSI – the EVDO signal strength. You know what this is, closer to –0 dBm the stronger the signal. There is a point at which trying to obtain more signal delivers diminishing returns.Throwing gobs of money and time trying to get a –75 signal down to –65 will not gain you that much. Especially if your Ec/Io is high. Low RSSI and High Ec/Io = bad, Low RSSI and Low Ec/Io = great.
PER – Packet Error Rate. Data being sent/received from the tower. Perfect, again is 0%. A small increase here (3-5%) will not be a big issue. Get above that and your latency starts suffering and speeds are erratic. This can be caused by the towers connection as well as many of the same factors that cause high Ec/Io. The bottom data in the Field Test relates to cell towers around you and the sector antennas on them, called PN’s or Pilot Numbers. These are numbers that identify the antennas on different towers and is illustrated thusly:

So keep these three parameters in mind when you get up there on the roof and start tweaking. Remember, a low dBm reading does not guarantee great speeds. Ec/Io and PER are important factors as well. Try for a balance between all of them to get the best experience you can with mobile broadband at a fixed location.

Pointing the antenna directly at the tower does not always result in optimum signal. If there is multipath (radio signals arriving at the receiver via different transmission paths), the direct and reflected signals are often opposite in phase, which can result in a significant signal loss due to mutual cancellation. Trees, buildings, mountains, and other terrestrial  phenomenon cause this. Seasonal changes with leaves present or not can often require a re-point if they are in your path.

Keep an eye on the Field Test data and point the antenna accordingly.