Antenna mounting question

[Cisco1619]

I am still new to wireless. I have been studing for my CCNA Wireless for about 6 months now so I still have a lot of questions.

Right now I have to deploy some new APs. We are using 3502e APs. I have a qustion on how to mount antennas for these access points. I have to make a mounting bracket the new installations. What was done with the previous APs was to mount a unistrut beam to an I beam in the building. There is 2 AIR-ANT-1728's and 2 AIR-ANT-5160V-R antennas mounted straight out on the unistrut. Then they put a T bracket on the unistrut and mounted a second bar 90 degrees from the main bar and connected the third 1728 and 5160 antennas on the second mounting bracket. So we have 4 antennas in a row, and two off to the side 90 degrees from the other 4 antennas.

My question, is this OK to have them this way, or would it be better to have all 6 antennas in a straight line when I fabricate my new AP brackets?

Here is a picture of what I am talking about. This would be looking at it from above. Any thoughts on what would be the better mounting solution?

Current                                                       New Proposal

__________o__o__o__o_                     _________o__o__o__o__o__o  

          |               AP                                                       AP

          |

          |o

          |

          |o   

Thanks again for any help! It is greatly appreciated!         

[Scott Fella]

Well how I have don't this before is to use a conduit in a vertical position and then have a uni strut on the top and bottom parallel to the ground. Then I mount the 3 2.4 in the top and the 5ghz on the bottom but that doesn't matter. Then evenly space the antennas no more than 3 times of the wavelength. So they will be close to each other. You can measure the distance between the antenna ports to calculate the distance of 3x. Having the two uni struts keeps it balanced especially if your mounting this 3' or so from a column. If your just mounting then downward from a ceiling I beam them put them in line. 3 5ghz then the 3 2.4ghz.

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[Cisco1619]

If they are farther than 3 wavelengths apart, will it affect performance? Our current environment, with the t mounting scheme, is 5.0, 2.4, 2.4, and 5.0 on the main beam. The 5.0 are much farther apart then 3 wavelengths right now.

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[Scott Fella]

Rule of thumb is no more than 3 wavelength for diversity. So yes it would affect how diversity works.

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[Scott Fella · Accepted solution]

This doc mentions 1 to 2 wavelength but that's playing it safe.

http://www.cisco.com/en/US/docs/solutions/Enterprise/Mobility/emob41dg/ch9_Voic.html#wp1073907

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[Scott Fella · Accepted solution]

Here is another document.

http://www.cisco.com/en/US/tech/tk722/tk809/technologies_tech_note09186a008019f646.shtml

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[Cisco1619]

There is some really good information in there, thanks! Looks like either option will work if I get the spacing right. I appreciate the help on this!

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[Scott Fella]

No problem. Good luck on the install.

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