I have a case study: WiFi outdoor for Marina:

[nguyen_minh_duc]

 With maximun distance need coverage about 100m. I wonder to chosse T300, T300n or T300s suitabble  for this case. please help me

[john_d]

From my experience with the 7782's, the omni outdoor AP's like the T300 is best if you can mount it dome down in the center of your desired coverage area. If you were hoping to mount it on wall or against some other surface and have the dome point "towards" the intended coverage area, then the T300s or T300n are probably more appropriate. But at any rate, based off the photo alone it's difficult to guess which antenna pattern is correct for you. As Michael said, hopefully you can work with your reseller to get demo units and come up with a good plan, as it sounds like you're making a major investment to cover this area and you don't want regrets down the road of whether or not you got the right model.

[seanmuir]

You can calculate your effective AP distance by means of link budget calculation.

Effective distance can be based on the following criteria:

EIRP - Effective Isotropic Radiated Power (this varies depending on the area of world you are deploying your network)

EIRP can be a combination of the following (dependant on your regulatory guidelines):

AP Antenna Gain
AP Antenna Diversity Gain - based on that number of AP antennae i.e. 2 x 2, 3 x 3 etc
AP TX Power setting
Beamforming Gain

The remaining values which contribute are as follows:

Client Antenna Gain
Bit Rate requirement at the client end
Application usage - can drive the Bit rate requirement
Bandwidth requirement to the client
Number of concurrent clients

Once you have determined the above you can then aim towards ensuring your network is designed correctly

I can provide a Link Budget Calculator if required

Note: Coverage is nothing without performance