What is the job of a radio transmitter

[ASidd]

I am kind of confused. Does the radio transmitter modulate the waves or change it into alternating current. If it does both then which one is done first?

Thanks for your help.

 

[cepheid]

I am kind of confused. Does the radio transmitter modulate the waves or change it into alternating current. If it does both then which one is done first?

Thanks for your help.

I wouldn't claim to know all of the details, but basically taking AM as our example (for simplicity), I would say that there has to be equipment that does all of these things. The sound waveform has to be transformed into a time-varying electrical (voltage) waveform by a pressure transducer of some sort (but that's just a microphone). Then this time-varying voltage signal (which contains the actual speech or sound information) has to be modulated by multiplying it with the carrier wave (a voltage waveform of constant frequency). According to one source I just found, http://www.fas.org/man/dod-101/navy/docs/fun/comsuppl.htm, the carrier wave might be generated by a type of electronic circuit known as an oscillator, http://en.wikipedia.org/wiki/Electronic_oscillator, and that would be part of the transmitter electronics. Also part of the transmitter electronics would be the circuit to combine the carrier wave and the signal waveform, to produce the AM waveform. Then, I guess, as the last piece of the puzzle, you'd use this to drive an antenna to produce EM waves.

Actually, the Wikipedia article for radio trasmitter seems to corroborate what I'm saying:

http://en.wikipedia.org/wiki/Radio_transmitter#Description

EDIT: The "How It Works" section of that article seems even more like what you want. It explicitly states that both the oscillator (that generates the carrier wave) and the modulation circuit (that piggy-backs information onto it) are considered part of the transmitter.

 

[CWatters]

http://www.g4prs.org.uk/Foundation Course Material/Transmitter_Block_Diagram.htm