Which antenna to use for a wireless WAN link?

[connie]

Hi All

I am setting up a wireless link to one of our remote sites, and I am making use of two Cisco Aironet 350 bridges (50mW transmission power).

The distance between the two sites is 4km line of sight. The remote site is three stories high, while the primary site is 22 stories high. The antennae on both sites will be mounted on the roof of each building.

My requirements are that the link be reliable and fast, since it is a WAN link. Now for the question:

Which type of antenna would be the best for my purpose? Should I look at a Yagi-type antenna, or a parabolic grid/dish antenna?

Bearing in mind that we have winds that can reach up to 100km/h, and that we're about 1km away from the sea, the antenna would also have to be relatively weather proof - unless we can somehow enclose it in a weather proof shielding.

[scottmac]

Either of the skeletal antennas (Yagi or Parabolic) would work. If your location is subject to much rain / snow, the parabolic would probably be the best bet to reduce rain fade.

The wind load for either is pretty low, but you should use a stiff mast & mount.

The parabolic has a tighter beam, if the mast / mount can wobble at all, you may lose some signal strength.

As long as you're planning, don't forget to use a fiber degment between your LAN and the wireless equipment to protect from lightning / environmental static / near hits.

Good Luck

Scott

[jens.neelsen]

Hi,

the first question is what is allow by the local regulations. If you are in Europe the maximum EIRP (Emitted Isotropic Radiated Power), the power level in front of any antenna, is limited to 20dbm or 100mW.

If you check this with the bridge range calculation excel sheet from cisco.com you find that for 4km distance you have to use two dish antennas (21dbi gain). This means that you have to set the power level on the two wireless bridges to 1mW (0dbm). Then you will stay in the EIRP limit.

Yagi antennas do not have enough gain (13dbi) for the distance of 4km. A better antenna goes further than more transmitter power.

With kind regards

Jens Neelsen

jneelsen@ieee.org

[Hunt.Lee]

Sory guys,

On another note, can someone please recommend / advise what equipment would I need if I have 1 AP with 6 clients but they are in 1km range?

I'm kind of a newbie in wireless area, hence would appreciate any help available.

Cheers,

Lee

[scottmac]

Again, without seeing the actual setup, area, etc it's pretty much all speculation.

GENERALLY SPEAKING, you'd want the highest gain omnidirectional (vertical stick) at the central point, with yagis or parabolics at the periphery aimed at the omni in the middle.

Antenna altitude is usually a good thing (higher is usually better). The trade-off is the amount of cabling it takes to get the antenna up to altitude - longer cabling means more loss (less signal).

If you can locate the APs as close to the antennas as possible, and use a segment of fiber on the wired side to isolate your LAN from possible environmental hazards, you have a pretty good shot at making the trip.

As mentioned above, you should check to see what the local and federal laws / rules / regulations are for your area.

You may be able to contact your local Cisco office for configuration assistance (or a qualified / authorized distributor or VAR).

Good Luck

Scott

[ggiannattasio]

Pls browse on Cisco CCO to find the utility calculator for wireless links.

www.cisco.com/application/vnd.ms-excel/en/us/guest/products/ ps458/c1225/ccmigration_09186a00800a912a.xls

also

http://www.cisco.com/en/US/products/hw/wireless/ps458/products_tech_note09186a008009459b.shtml

There you will find according RF cable length, antenna type, distance of buildings, two important values

a) the db margin calculated, and

b) Fresnel zone clearence needed.

bear ni mind that bridge 350 reaches 100mw (20dBm )not 50 as you say. Did you consider the bundle "wirelss building to building kit" that is les expensive that purchasing all items separately.