Can i make a cheap CCTV wireless camera to transmit longer distance?

I want to built a strong video transmitter and receiver. So i am planning to use a CCTV wireless camera. 
Does anyone have any idea of how to upgrade a wireless camera transmission or receiving?
Or can i build it from each electronic components? Like from sketch? 

Just improve the antennas. Add cantennas at one or both ends.
Your best option is to by a signal amp for the system. Trying to design one or tweak the existing circuit is very complicated. Best DIY solution would be to give each end of the system better antennas. A directional system like a pair of simple cantennas is a great solution given you have a clear line of site between the 2.

Gotta be careful with this sort of thing. You don't want to run a foul with any government regulations. Broadcasting is heavily regulated by most governments and requires licences in many cases.