This DSP project describes a GNU Radio DSP and Operating GUI for an elemental SDR transmitter. This elemental transmitter emits an unmodulated constant carrier. There is no modulation capability with this DSP. An overview of a similar project that uses the same DSP to implement a signal generator is located here under SDR Projects: Signal Generator and Weak Signal Source
The DSP for a SDR transmitter or a SDR signal generator is a simple GNU Radio flow graph. The minimal DSP elements in a flow graph for this project are to link the data from a Constant Source block to the input of a SDR Sink block (SDR transmitter hardware). Once that simple flow graph is executed, the SDR Sink block will turn on and output RF determined by the frequency parameters entered in the Sink block Frequency field. What is missing from this DSP, to make this transmitter a complete radio transmitter, is a means to add modulation to the signal whether the modulation be Morse keying, a digital constellation, or voice modulation
The Operating GUI, as it is in any radio DSP project, is a major step toward implementing a useful and operationally satisfying transmitter. The Operating GUI permits control of the transmitter operating parameters in real time. The Operating GUI incorporates some of the functionality to turn SDR transmitter hardware into a useful transmitter: course and fine control of the output frequency, variable output level, and ‘on’ and ‘off’ control, all from the Operating GUI. The details of transmitter control from the Operating GUI are discussed in the SDR Signal Generator project, the flow graph, Operating GUI, and .grc file are here: Signal Generator and Weak Signal Source