To be able to build a small transceiver using the DIL-28 microcontroller ATMega328p programmed in an UNO is possible . It is i.e. usefull from a mountain top (SummitOnTheAir) to make a radio contact IF YOU ARE LICENCED FOR FREQUENCY USAGE !!! Illegal transmitting is an offence , heavely punishable possibly by yail !!!
It is small and light but don't expect too much, the ucontroller is not quite suitable and the modulation is less , but quit exceptional it is possible .
Allready a few years ago amateur radio operator Guido PE1NNZ developed very genious software as an extension to what was the QCX from QRPLabs . An extensive building description of the - uSDX - is made by Barb WB2CBA . Are you not yet an amateur radio operator , is just this the building project with which a new world appears ? There is allways somewhere around someone with a lot of antennas who will be so kind to help you further .
Look on internet for uSDX and open the pages of Barb WB2CBA