Why is my arduino acting like a radio? And is there a way to abuse this?
I did something like that a while ago. Hardware:



Code:

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


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.

If you hold the Arduino near an AM radio tuned to around 800 KHz you should hear a hissing toggling on and off (like Morse code) as the carrier is turned on and off for 0.5 / 0.3 second intervals.


  would there be a relatively easy way to pick up the signal using just an arduino and cheapo components? 


I think you might find making a receiver a bit harder than a transmitter.