This question is about digital voice modes that are used with AM / SSB / FM radios. Dstar , FreeDV , etc.
assumptions: pulse width modulation amplifiers can take a digital signal as input.
a software defined radio(SDR) is a sensor that can recive any kind of signal within a certain frequency range.
SDR demodulation is just software and can theoretically process any signal.
My question is , could traditional rf modulation techniques be removed entirely ?
Scenario: microphone in to computer such as microcontroller / raspberry pi I2C digital connection direct to PWM amplifier PWM amplifier transmits raw signal at RF frequencies in exact frequency range SDR set to receive any signal in exact known frequency range PC software detects PWM signal in frequency range and converts to digital audio signal PC outputs audio
There is no audio conversion except what is normally done by a PC when you use a microphone or speakers .There is no separate RF modulation like FM / SSB. The "modulation" is whatever the pulse width modulation of the amplifier is.
This would be like a class D audio amp with digital input from a pc except that the amplifier is connected to an antenna instead of a speaker.