Determine the vertical height in feet of antenna elevation

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Sep 12th, 2007
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I used to know how to do this, but I seem to have forgotten.

I am trying to determine the physical distance of an omnidirectional antenna in order gauge placement and power.

The antenna in question is AIR-ANT2430V-R and has the following properties:

3dBi Gain, Beam Width 360?H, 60?V, and has an indoor range of 153 ft at 54Mbps. It will be mounted to a steel girder that is 32 feet from the floor. I will do a survey when I can get one in hand, but in the meantime,I am trying to plan as best as I can for the install.

We will be replacing some Vivato panels that are in place at the moment

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scottmac Wed, 09/12/2007 - 15:06
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I'm a little fuzzy on what you are asking.


Are you asking if you measure from the top of the antenna (normal or inverted) or the bottom?


If you're trying to determine coverage from an antenna location, then (in this case) from the floor, site along a protractor (or make a sight-line) @ 60 degrees relative to the floor ... when the AP is in site, you have found your primary radiation coverage.


Some folks might make a 120 cone and suspend a representation of the antenna (or better yet, a light source) in the middle. If you are in the direct light path, you would be in the RF primary path.


Please try your question again ...


Thanks


Scott



ericgarnel Fri, 09/14/2007 - 06:08
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I am inquiring as to the vertical size of the "donut" of the particular omnidirectional antenna. I have an area @ 246,000 sq ft that I will be deploying several APs into in the near future.

The space has no columns and the ceiling consists of a grid work of steel beams, trusses, etc that support the roof. the lowest point to mount antennas in the area is 32' from the floor. I will do a survey 1st, but I was trying to speculate the best performing antenna for the environment. Ideally, I would like to use a 1250 for the survey, but can use a 1030 if needed. Granted, not all APs & antennas are equal.

scottmac Fri, 09/14/2007 - 12:16
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Much better, thank you.


There are some patch antennas on the market (I don't think Cisco has them) with a 180 degree hemisphere pattern.


Instead of putting them on the wall aimed down the hall, hang them from the ceiling pointed down.


If I can find 'em in my old links, I'll re-post with the link.


Good Luck


Scott


scottmac Sat, 09/15/2007 - 06:43
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I can't find anything in the old links I had.


I did some quick scans and found these:


http://www.hyperlinktech.com/web/hg2403cu.php

http://www.hyperlinktech.com/web/hg2403mgu.php


These might work, but the site doesn't give any Smith charts to judge the patterns ... might be worth calling or emailing them for more specs:


http://www.antennasystems.com/



And, of course, my personal favorite dish & antenna guys, nothing but professional / commercial grade stuff (Andrew Corp):


http://www.andrew.com/products/trans_line/radiax/

http://www.andrew.com/products/antennas/in_building/cellmax.aspx



For a convention center, you might want to consider an "RF Distribution System" versus a constellation of Access-Points. Probably worth a look ...

And / or use Radiax, set up in zones.


Give them a call, maybe they'll come out for a look ...


Because of the height, you don't really want or need much gain ... the first two antennas I linked to have 180 degree radiation (but still a donut pattern with a null in the middle ... I'd expect that normal multipath would cover the null, or a pair in diversity mode.


Any radiation going up or directly sideways would basically be a waste ... I was looking for something with a 180 degree pattern, with the major lobe being as wide as possible .... then aim it straight down from the ceiling.


Unfortunately, I don't think a patch with 60 degree coverage is wide enough and you'd end up with micro-cells (i.e., need too many APs to be practical).


Another approach you might want to look at would be something like 90 degree sector antennas around the periphery aimed toward the center. Instead of mounting them vertically, mount them horizontally at the junction of the wall and "ceiling" (at the girder level)


Sector antennas tend to have fairly tight boundries in both planes such that you could zone a region with one or more pairs of sectors ... and / or back-to-back 90 degree sectors as a "spine" down th emiddle of the hall paired with another sector at the perimiter wall aimed in.


-------------------------------

])...........([])............([

|..............................|

|..............................|

])...........([])............([


]) = horizontal sector aimed in the ) direction - or ( direction


(and so on. Ignore the dots, they're just thre 'cause the Cisco site Trims / Chops / Chomps the white space).


Or stagger them peripheral , Spine, peripheral, spine, etc to cover the peripheral area well where conventioneers tend to aggregate.


There's a lot of variables, I know you know that from your other posts .... I'm just trying to offer some alternatives that I've seen that seemed to work for the specific setup.


Something to keep in mind is that any significant deviation in design or implementation from the Certified product from any vendor may render the certification invalid ... depending on the sensitivities to legal things, may require another certification (compliance with Federal / FCC and regional / local radiation & interference rules).


Good Luck


Scott


Rob Huffman Sat, 09/15/2007 - 08:00
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Hi Scott,


Very nice work! Always a good Saturday morning read :) 5 points for you my friend!


Take care,

Rob

ericgarnel Sun, 09/16/2007 - 08:00
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Thanks Scott, this is a big help. 5 points from me as well

ericgarnel Mon, 09/17/2007 - 06:14
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My original plan for the Cisco deployment was to mount them around the periphery with directional antennae. Currently, we have the Vivato Panels mounted that way. When we first deployed the wireless, we were not allowed to mount anything to the girders, but that policy has changed recently. My only concerns about wireless from the periphery is that in such a dynamic environment, where one day there will be rows and rows of exhibitors separated by pipe & drape w/ simple booth setups, to the next day where there will be rows of RVs, campers, cars, boats, even a few helicopters from time to time. The path would have some obstruction in the way at any given time. The vivato panels are phased array units with 6 200mw radios, each attached to a 21dBi antenna. The eirp for b is @ 41dBm and @ 37dBm for g. The panel has 90 h & 12 v pattern. They handle the environment pretty well. The whole reason we are replacing them is for product support, location support and better manageability, not to mention a longer product life line.


I like your idea of a hybrid setup it is definitely workable in our environment


srosenthal Mon, 09/17/2007 - 07:11
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I had a very large warehouse that I need to provide coverage for and the only place to mount the AP's was in the ceiling girders. What I did was mount the AP on a small plywood board and then used the AIR-ANT2506 mounted right under the girder. I strapped the antenna to the girder horizontally which provided plenty of coverage with no cone under the antenna.


Seth

ericgarnel Mon, 09/17/2007 - 07:36
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That is similar to what I was planning on doing with the space.

How high were the girders? Ours are 32 ft from the floor, subtract @ 3ft for the average table height = wifi client @ 29 ft below antenna height. I am considering placing a few omnis towards the middle and directionals around the periphery. I'm sure I will find a creative solution.

ericgarnel Mon, 09/17/2007 - 11:15
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The not-so-technical alternative solution.


I was able to dig up some building plans to determine the height of some existing APs in another area. We have 1020 APs with the internal antennae working just fine in a ballroom with a 29 foot ceiling height.


Granted,

The 1020 & the 1252 differ greatly, not to mention that the 1020 has two, 5.5 dBi antennas built in. Still, I put a request into our local Cisco SE to get some 1252s with various antennae, etc for survey purposes.

"deploy wifi in your building....The quickest way to learn about architecture & construction"

scottmac Mon, 09/17/2007 - 11:36
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Since you've led us down the path of non-technical alternatives ;-} ... try this out when you get a chance:


A CD (as in 'Compact Disk') works perfectly as a reflector. You will need to "tweak" a little to get the correct distance from the primary emitter, but it works surprising well.


You may find that they work well for directing otherwise wasted (think upwards)signal back to a useful area.


Of course, done improperly, it can also create a nightmare of multipath (hint for the wireless instructors out there).


Not very durable for outdoors, but I can't thnk of any cheaper or easier in a pinch ...


Glad to hear you're on your way ....



Good Luck

Scott

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