if the signal is too weak, you'll need an outdoor antenna.
outdoor antennas are usually sold by two ways:
1. the frequency you want to grab from the air.
these are usually divided into a low (vhf) and high (uhf) section (but some antenna shapes are tailored to a specific frequency)
2. next comes the distance from your location to the broadcast antenna.
the antenna's will be categorized by distance (50miles / 75 miles / 90 miles / etc)
they will also begin to recommend an amplifier to get the most out of the antenna.
to get the best possible result, you probably want a setup that will work in the rain.
i remember my time with antenna television, the signal was bad in the day and better at night.. and if it was raining, sometimes it helped and sometimes it made it worse.
**edit**
another thing..
sometimes you cant just point an antenna into the general direction of all of the broadcast antennas.
it might be worth your while to get an antenna rotator.
then carefully align the antenna to the angle mentioned in the results (if that website doesnt give the azimuth, there is another website that does)
once the angle is aligned.. go in and make a dot on the knob and a dot on the outside of the knob.
when you are done, you will have one dot on the knob with a few dots on the outside to make rotating the antenna as easy as lined up dots.
this could expand the television channel selection considerably.. and it helps when there is nothing on television to expand the selection.