Re:Welcome to the World of Software Defined Radio (2016)
by kazinator on Thursday September 21, 2017 @02:53PM
(#15306341)
> Sound waves and radio waves are of completely different carriers.
(ITYM "media"; a carrier is a waveform onto which a signal is imprinted.)
In an electronic circuit it's just frequency, whether the waveform came from a microphone, or from a radio-frequency oscillator.
When you mix audio into a carrier to produce a radio signal, it's all just math functions realized in the same medium: the medium of voltage/current changes versus time.
In radio, audio frequencies that were once carried through the air are imprinted, via electronics, onto radio frequencies.
For instance, a 500 Hz audio tone modulating a 700 kHz AM carrier creates 700.5 kHz and 699.5 kHz side bands (chopped to just one side band with SSB (single side band) encoding). The fact that there had been a sound wave moving through the air is now imprinted in the radio wave medium.
"Low frequency" in radio basically starts in a range that is outside of radio, yet high enough to be usable for carrying audio signals.
(ITYM "media"; a carrier is a waveform onto which a signal is imprinted.)
In an electronic circuit it's just frequency, whether the waveform came from a microphone, or from a radio-frequency oscillator.
When you mix audio into a carrier to produce a radio signal, it's all just math functions realized in the same medium: the medium of voltage/current changes versus time.
In radio, audio frequencies that were once carried through the air are imprinted, via electronics, onto radio frequencies.
For instance, a 500 Hz audio tone modulating a 700 kHz AM carrier creates 700.5 kHz and 699.5 kHz side bands (chopped to just one side band with SSB (single side band) encoding). The fact that there had been a sound wave moving through the air is now imprinted in the radio wave medium.
"Low frequency" in radio basically starts in a range that is outside of radio, yet high enough to be usable for carrying audio signals.