Antennas

[agent007]

If I install a Cisco AP with detachable antennas, do I have to install two higher gain antennas for increased range, or I can I disable one of the antennas?

Thanks!!!

Eternally dumbfounded about RF

[johnnyr]

I'm far from an expert yet, but I'll share what I know...

The reason for the two antennas is to eliminate multi-path, where the same signal may take different reflected paths (therefore of different path lengths) to arrive at the access point. If those two paths are a multiple of 1/2 wavelength different, they will cancel out and make a "hole" in the signal.

If you disconnected one of the antennas and connected a directional antenna, everything should still work just fine. Because of the directional antenna gain, multipath should not be an issue, but the second antenna would still be doing its work if it had a chance.

[agent007]

Thanks for the reply. This AP will be set up with a omni or a sector antenna in a highly metallic outdoor area, with many different types of vehicles parked nearby. I may run into multipath problems...........

Thank you.

[mupdike]

If you are going building to building, higher gain antennas will make a 'flatter' signal reducing the possibilty that the metallic objects could cause a problem. On way to determine if there will be a problem is to determine your "fresnel zone", this is the zone in which blockage cannot be introduced without causing loss of performance. The way to figure out this area is: r=43.3 * (square root of)(d/4f) where: r=radius of Zone (in feet), d=distance of link in miles, f=frequency in GHz (r=measurement of Fresnel Zone’s widest point).

If you are trying to cover a zone for clients, increasing the gain causes a flatter signal which makes it easier for clients to be out of the range of reception. With the Omni think of a pancake for high gain (round and fairly flat), or a ball for low gain.