A software-defined radio (12) includes a transmitter (20) having any number of upstream modules (30) and any number of downstream modules (34). The upstream modules (30) perform signal processing on input signals (28), and the downstream modules (34) provide an RF interface for processed signals (58). The upstream modules (30) and downstream modules (34) couple to a common intra-transmitter signal transporter (32), which may be implemented as a bus. Programmable transmission parameters (60) which program the downstream modules (34) to generate a communication signal (18) exhibiting desired attributes such as frequency and keying are mingled with the processed input signal (58) in upstream modules (30) to preserve timing. The programmable transmission parameters (60) are extracted in downstream modules (34), and applied to the communication signal (18) at the timing specified by position relative to the processed input signal (58).