ADSL2+ Modem/Router and external outdoor antenna

I need a ADSL2+ Modem Router that works with a Frontier DSL connection.

I need to cover athletic fields at a high school, and I have a DSL connection in the crows nest of the football field. Our students video the football games put it online live through livestream.com. Works great for the football games, but they want to start doing the same thing for softball and baseball, so we need to boost our signal to reach those 2 fields. I can get a signal from our softaball/baseball fields, but it's weak - to weak for video upload. We're just using the Frontier (the DSL provider) modem router included with the DSL, but it uses an internal antenna so we just can't add an external antenna to it to boost the signal.

I looking to get a modem/router that I can put an external directional outside anntenna on to boost the signal to those 2 fields.

The modem also must have Wap2 type of encryption.

Any thoughts/ideas/reccomendations? I'm looking for a place to start searching for what we'll need. If I could get some links to specific hardware or phone numbers to places I can call that would be great.