exempt rf

I have decided to undertake a project in which I wirelessly connect computers in my local area. While I know I can easily purchase units, the whole idea is the learning experience. So my main question is: What licence-exempt RF would be the best for a range of approximately ±3-5km. I know the one range is the 418-433MHz band, but I heard from I friend (I don't know how reliable he is) that you can get an extremely far distance with 408MHz (but this is outside the licence-exempt range). I know that the type and length of the antenna used will also have a great affect on range and help in this regard would be appreciated as well.

Sputnik

With these geographic ranges you will need high gain antennas and possibly lower bit rates than you desire. If you want to learn things try a simple project first where you go short ranges using the RS232 ports being connected together via radio. This can be done at lower frequencies where there are less hazards to avoid in hand constructing the radio circuits.