Diddy1
join:2003-07-19
Sidney, NE
| RF propagation on sector antennas
I've installed the 3 sectors and 1 grid for my first access point location. However, I have a railing that I installed 2 90* sectors and the grid(backhaul). My questions is, what distance out from a 90* antenna does the signal start to propagate sideways from the center point? I hope this makes sense. I'm just wondering if the grid that is 3' off the side of on of the sectors will block the signal from that sector. I would guess it's further away than will be an issue. The railing the grid is mounted on is slanted back a little making it sit back a few inces from the sector.
Thanks,
Aaron |
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John Galt
Forward, March
Premium
join:2004-09-30
Happy Camp
 ·CenturyLink
| Any metal that protrudes into the frontal plane of the antennas radiated pattern affects that pattern...especially at this close distance. Remember, a "90 degree" antenna is one that has the -3dB points at 90 degrees (total, +/- 45 degrees off of the main axis)...the radiation pattern is much wider than that.
For example:
»www.hyperlinktech.com/web/pdf/hg···-090.pdf
You might consider moving the grid above the sectors. Even a few vertical feet would help...of course more is better.
Rule-of-Thumb...antennas should be as far apart as possible, unless interaction is desired (a phased array, for example).
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A is A |
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Diddy1
join:2003-07-19
Sidney, NE
| said by John Galt  :Any metal that protrudes into the frontal plane of the antennas radiated pattern affects that pattern...especially at this close distance. Remember, a "90 degree" antenna is one that has the -3dB points at 90 degrees (total, +/- 45 degrees off of the main axis)...the radiation pattern is much wider than that. Ok, cam you elaborate on the -3dB points? I'm going to try to locate the grid elsewhere, but I'm still learning the theory and what not behind antennas so any info. you can give will be properly digested 
Aaron |
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inova
join:2006-05-03
Macnutt, SK
| John's link shows the -3db points pretty good. I have been installing 90* sectors and have found that I can get an excellent signal at 12 miles straight in front and the same signal strength at 6 miles at 90* to the sectors center line. They are effectively covering 180* for me. Uniformity of coverage is not a major issue here. However your original question, I believe, has more to do with how the arrangement impacts on performance. This is where I am uncertain. I would like to know how you would properly test your performance with respect to antenna arrangement. My ping times are relatively constant with the odd spike and no packet loss. My throughput is more than adequate for my network. Are these the only issues to consider? If I was to improve my antenna arrangement what performance improvement might I expect? Improved throughput or lower ping times? Both? |
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John Galt
Forward, March
Premium
join:2004-09-30
Happy Camp
·CenturyLink
| reply to Diddy1
This should help...
As you can see there is still a significant amount of energy 90 degrees off-axis.
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A is A |
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lutful
Premium
join:2005-06-16
Ottawa, ON | If this sector has 12dBi nominal gain and radio TX is 24dBm, we will get (24+12-10)= 26dBm or 400mW EIRP almost 100 degress away from dead center? |
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Diddy1
join:2003-07-19
Sidney, NE
1 edit | reply to Diddy1
Well to through in a little real-world stats. I get a connectable signal 5 miles out LOS directly to(45*) the side of the antenna. I haven't gone further as there is no real road to travel on
Strangely enough, I have a 14dBi sector antenna facing Wst and I can get strong signal direclty East of it 4 miles out.
This signifacntly hinders my idea of reusing a channel vs. East West but oh well. I don't have any firm numbers to post so I'm not sure if this is really useful data. The setup is undoubtedly performing better than spec. and what I anticipated. I now have the entire area lit up in the 2.4Ghz spectrum. I know it might sound like a spectrum hog, but everything is within FCC spec.
Aaron |
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