Re: Digital transmitter:
Hi,
This is a very open ended question. But what I would do is this. First get a book that goes into the basics of digital radio design. As a suggestion you could look at:
Transceiver and System Design for Digital Communications, 2nd edition
By: Scott R. Bullock
This a good overview. Then go to the websites of the manufacturers who make these parts and look at the datasheets and application notes. They will give you good circuit ideas.
The basic buiding blocks of a digital tranmitter would be power amplifier PA, IQ modulator, VCO, PLL and baseband circuitry.
You have to decide things such as frequency of operation, range requirement, data throughput etc.
Manufacturers of these parts would be analog devices, maxim semicoductor, RFMD, TI to name a few.
There's a lot to cover on this subject, far more then can be written on the forum. So dig through and have fun.