How can i design RF transmitter circuit?

i am a student in nationlink industrial i need to test rf transmitters and receivers

There is an enormous difference between designing a transmitter and testing transmitters and receivers. Which is it you are interested in?
RF engineering is a specialized field of analogue and digital electronics.
Testing on the other hand, requires a different skill set. You have to understand some RF principles, particularly in the area of transmission lines and RF radiation, but it comes down to using specialized testing equipment normally. In either case, there are international standards that equipment has to be designed and tested against,
cheers,
Richard

I understood there are great difference between testing and designing.
but what i mean is designing i want to now if there is a simple homemade TX and RX with long range
Although there are several ways to design, i am trying to find the simplest way using basic components. Please i need a help if there is a simple circuits,
thank you

What sort of range, in general, HF will do over the horizon, above that you are line of sight.
Check out the bands allocated to civilians in your country. There will be HAM, CB, and ISM.
They are scattered from HF up to UHF frequencies. The HAM bands usually only allow voice with a special license, you need to check that out. There is plenty of information on the WWW, and plenty of books published on building HAM gear.
ISM is used for short range data transfer, there are plenty of transceiver ICs available operating in this band, and even built up boards.
In any case, you can't blast out a signal on a transmitter at any old frequency or power, there are emission standards you must comply with to avoid interfering with other users,
cheers,
Richard

I think, in the simplest form RF transmitter will use HT12E and a RF Tx, I tried to build a RF controlled Robot, but didn't find any easy way for transmitter and receiver, other than this:
"RF Controlled Robot(Possibly the simplest RF trasmitter used)":http://circuitdigest.com/electronic-circuits/rf-controlled-robot-without-microcontroller
I am sharing it here because I am quite impressed with the Demonstration, you can find the easiest (possibly) transmitter here.
Also keep posted here if you find any other simpler design, so that I can also improve my machine.