The antenna pattern charts are thoroughly confusing because of MIMO (also known as 802.11n). In order to distinguish between the two independent signals or beams used by the MIMO in the NanoBeam, Ubiquiti calls one signal "vertical" and the other "horizontal" in honor of their relative polarization. The direction, relative gain, and pattern are called "azimuth" and "elevation". When used with
802.11a/b/g which use only one signal, I think (which means I'm too lazy to check) that only the "vertical azimuth" and "vertical elevation" patterns are used. In other words, you're using the wrong pair of beam patterns. Fortunately, the other two are sufficiently close so your numbers will be unchanged.There is no distance. That's not how an antenna pattern works. The outer ring is defined as 0dB, which is a reference level established by the strongest signal in any direction. Every other point on the pattern is at a signal level that is less than 0dB.
Doing it that way is highly convenient. For example, let's pretend you aim the dish antenna at a distant receiver. You maximize the signal by swinging the antenna. If it's designed correctly, the peak signal should be when the dish is pointed directly at the distant receiver. If not, you have what's called a "bore sight error". You then scribble down the maximum signal level (in dBm). You can then use the antenna pattern to calculate the signal level at any point of the compass (azimuth). If the outer ring were a distance, which makes all the points on the plot absolute values instead of relative values, you couldn't do that.
Perhaps it would be helpful if I explained why I have a preference for calculation over "it just works". One problem with my calculations are that they are the best case numbers. Everything that brings the numbers closer to reality makes the range and coverage worse. If I threw in reflections, Fresnel diffraction, interference, component variations, tolerances, and just plain lies on the data sheets, the range would be less and the coverage patterns smaller (or less coverage). The question my calculations answer is "Under ideal conditions, does this thing have a chance of working"? If it doesn't pass that test, I usually don't bother trying it and look for a better solution.
Of course, something unexpected will always appear that were not considered in the calculations. In this case, it was a steel fence. I still don't know exactly where it is located or what effects it might have on Fresnel zone diffraction and any reflections. I'm also not sure about how much the brick wall attenuates the signal. Looking at the photo, I'm wondering if the 150ft is a measurement or an estimate. Any or all of these can screw things up, but probably won't because of the rather large fade margin. If I don't run the numbers first, to see if the system has a chance of working, I'll never know if I have a huge fade margin where almost any change will not have a major impact, or if I'm skirting the bitter edge of failure with a marginal system.
Incidentally, I just realized a made another screwup. My fade margin calculations were from: Ubiquiti Nanostation LocoM2 -> Typical smartphone I'm so used to symmetrical systems, where I have identical bridge radios at both ends of the link, that I forgot to calculate the fade margin going in the opposite direction. The LocoM2 transmits at +23dB while the smartphone might manage +20dB. In this case, a loss of -3dB of fade margin will have little effect on the rather large fade margin, but I should have calculated it anyway.
I don't understand it either. The first few slides somewhat explain how AirMax (TDMA MIMO) works: I vaguely recall reading a white paper on the topic, but can't find it right now. Very little on the UBNT forum on the topic.
At this point, I usually dig through the available patents for clues, but dinner beckons:
If he has both another LocoM2 radio, and a mixed bag of client computers, he's screwed. It's one or the other, not both at the same time. In his case, there is no 2nd LocoM2, so the obvious choice would be to turn OFF AirMax, thus losing the speed benefits of
802.11n.