0Re-designBest Answer 8 years ago ReplyUpvoteThis has been asked before. Maybe a different distance but similar. I seen to remember that the best answer we came up with was that it was better to just go out an buy a pair. Even the cheapest pair should have that range unless inside a building with metal walls. There is no easy way to build a set and you would spend much more than new ones cost. In the USA it is illegal to build a transmitter unless you have a license except for very very low powered ones under Chapter 15, and some other experimental allowances. These typically have 200 foot range or less.