Adjusting antennas

Answered Question
Feb 6th, 2007

Hi!

I have an aironet 1242AG access point, with 2x 2,4Ghz (AIR-ANT5135D-R) and 2x 5Ghz (AIR-ANT4941) antennas installed. I have the access point lying on a wardrobe, close to the ceiling. What is the best position for the antennas? Should they be straight vertical, or creating a V shape (between the 2 of the same frequency)?

I dont think to get a big gain out of this, but what are the guidelines?

Thanks a lot for anybodys time!

I have this problem too.
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Correct Answer by rob.huffman about 9 years 7 months ago

Hi Sakul,

In your case "straight vertical" would be the way to go. You might not even really need two of each unless your are trying to provide Diversity type coverage. Have a look;

You can use two antennas in Diversity mode but not to cover two different cells/areas. For most installations, if you just used one antenna connected to the Right-hand/Primary, RP-TNC connector you should be good, if you have some obstacles in the cell area you can try using Diversity mode(2x???? Antennas);

When you use a pair of antennas with matching characteristics to provide diversity for cell coverage in your facility, the guideline is to put those matched antennas at a distance apart from each other that is equal to a multiple of the wavelength of the frequency that is being transmitted. The 2.4 GHz wavelength is approximately 4.92 inches. Therefore, to support diversity on a 2.4 GHz radio with two separate antennas, the antennas should be spaced approximately 5 inches apart. The antenna pair could also be spaced at multiples of 5 inches, but the distance between should not exceed 4 multiples: reflected waves farther apart than that are likely to be so distorted and different in delay spread that the radio could not work with them.Because each antenna is selected by itself, both antennas must have the same radiation characteristics and be positioned to provide similar cell coverage.

From this good doc;

Multipath and Diversity

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

Cisco Aironet 2.4 GHz and 5 GHz Antennas and Accessories

http://www.cisco.com/en/US/products/ps6521/products_data_sheet09186a008022b11b.html

Hope this helps!

Rob

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Correct Answer
rob.huffman Tue, 02/06/2007 - 07:24

Hi Sakul,

In your case "straight vertical" would be the way to go. You might not even really need two of each unless your are trying to provide Diversity type coverage. Have a look;

You can use two antennas in Diversity mode but not to cover two different cells/areas. For most installations, if you just used one antenna connected to the Right-hand/Primary, RP-TNC connector you should be good, if you have some obstacles in the cell area you can try using Diversity mode(2x???? Antennas);

When you use a pair of antennas with matching characteristics to provide diversity for cell coverage in your facility, the guideline is to put those matched antennas at a distance apart from each other that is equal to a multiple of the wavelength of the frequency that is being transmitted. The 2.4 GHz wavelength is approximately 4.92 inches. Therefore, to support diversity on a 2.4 GHz radio with two separate antennas, the antennas should be spaced approximately 5 inches apart. The antenna pair could also be spaced at multiples of 5 inches, but the distance between should not exceed 4 multiples: reflected waves farther apart than that are likely to be so distorted and different in delay spread that the radio could not work with them.Because each antenna is selected by itself, both antennas must have the same radiation characteristics and be positioned to provide similar cell coverage.

From this good doc;

Multipath and Diversity

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

Cisco Aironet 2.4 GHz and 5 GHz Antennas and Accessories

http://www.cisco.com/en/US/products/ps6521/products_data_sheet09186a008022b11b.html

Hope this helps!

Rob

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