radio wave generation using arduino

Question

const byte ANTENNA = 9;

void setup() 
  {
  // set up Timer 1
  TCCR1A = bit (COM1A0);  // toggle OC1A on Compare Match
  TCCR1B = bit (WGM12) | bit (CS10);   // CTC, no prescaler
  OCR1A =  9;       // compare A register value to 10 (zero relative)
  }  // end of setup

void loop() 
  {
  pinMode (ANTENNA, OUTPUT);
  delay (500);
  pinMode (ANTENNA, INPUT);
  delay (300);
  }  // end of loop

It is just toggling the mode of the pin, so how it is related to radio wave generation?

Answer 1

This looks incredibly like the post on my page: Turn your Arduino into an AM radio transmitter!

As the page mentions:

The 16 MHz clock is divided by 10 (that is, 1.6 MHz) and that is used to toggle pin 9 at that rate, giving a frequency of 800 KHz, since one toggle turns the output on, and second toggle turns it off.

These are the important lines:

  // set up Timer 1
  TCCR1A = bit (COM1A0);  // toggle OC1A on Compare Match
  TCCR1B = bit (WGM12) | bit (CS10);   // CTC, no prescaler
  OCR1A =  9;       // compare A register value to 10 (zero relative)

Timer 1 is set up to run at 800 kHz. That is a radio frequency. The toggling code just turns the output on or off as a simple form of "keying".