Can I transmit to several FM radio channels concurrently using one digital transmitter?
Yes, it is possible. The approach that I would probably take would be to use a small-to-medium size FPGA to do the DSP (basically 100 DDS generators), a high-speed (250 MHz) DAC, and a reasonably good LC bandpass filter at the output of the DAC.



This could be interesting: I did some digging, and it is now possible to do general-purpose programming on the GPU in a Raspberry Pi, and it is also possible to use the (hidden) DPI interface to drive a VGA display. Therefore, it might be possible to do this entirely on a Pi Zero, with the only external hardware required being the bandpass filter mentioned above.