Arduino CW beacon @ 1337 kHz

/*
http://forum.arduino.cc/index.php?topic=8456.0

Based on some work found on this board
at http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1169088394
and http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1166896036

I'm pleased to present a simple beacon, broadcasting Morse code over the radio airwaves.
It works by using an assembly increment on PORTB in the fast loop in the broadcast function.
The least significant bit toggles once per loop, the second toggles every two loops,
the third every four, and so on.
Just run the code and plug a length of wire into Digital Pin 8 and tune your AM dial to around 1337 kHz.
You can also get 1337/2 kHz on Pin 9 and 1337/4 kHz on Pin 10, etc. but this will probably be off your dial.
The LED on Pin 13 flashes the message too, if you like to look at the pretty lights.
*/

long millisAtStart = 0;
long millisAtEnd = 0;

//period of shortest broadcast (256 port changes)
const long period_broadcast = 8;

// number of period_broadcasts in one 'dit',
// all other lengths are scaled from this
#define LENGTH_DIT 64

const int length_dit = LENGTH_DIT;       //number of periods for dit
const int pause_dit = LENGTH_DIT;        //pause after dit
const int length_dah = 3 * LENGTH_DIT;   //number of persots for dah
const int pause_dah = LENGTH_DIT;        //pause after dah
const int length_pause = 7 * LENGTH_DIT; //pause between words

void dit(void);
void dah(void);
void pause(void);
void broadcast(int N_cycles);
void dontbroadcast(int N_cycles);

// ### INC ### Increment Register (reg = reg + 1)
#define ASM_INC(reg) asm volatile ("inc %0" : "=r" (reg) : "0" (reg))

void setup()
{
  Serial.begin(9600);
  DDRB = 0xFF; //Port B all outputs
  // Do one dit to determine approximate frequency
  millisAtStart = millis();
  dit();
  millisAtEnd = millis();
  Serial.print(millisAtEnd - millisAtStart);
  Serial.print(" ms/dit, freq: ");
  Serial.print( (length_dit + pause_dit) * period_broadcast * 256 / (millisAtEnd - millisAtStart) / 2 );
  Serial.print("kHz ");
  Serial.println();
}

void loop()
{
  dah();
  dit();
  dah();
  dah();
  pause();
  dah();
  dit();
  dah();
  dah();
  pause();
  dah();
  dah();
  dit();
  dit();
  pause();
  pause();
}

void dit(void)
{
  for (int i = 0; i < length_dit; i++)
  {
    broadcast(period_broadcast);
  }
  for (int i = 0; i < pause_dit; i++)
  {
    dontbroadcast(period_broadcast);
  }
}


void dah(void)
{
  for (int i = 0; i < length_dah; i++)
  {
    broadcast(period_broadcast);
  }
  for (int i = 0; i < pause_dah; i++)
  {
    dontbroadcast(period_broadcast);
  }
}

void pause(void)
{
  for (int i = 0; i < length_pause; i++)
  {
    dontbroadcast(period_broadcast);
  }
}

void broadcast(int N_cycles)
{
  unsigned int portvalue;
  for (int i = 0; i < N_cycles; i++)
  {
    portvalue = 0;
    do
    {
      PORTB = portvalue;
      ASM_INC(portvalue);
    }
    while (portvalue < 255);
  }
}

void dontbroadcast(int N_cycles)
{
  unsigned int portvalue;
  PORTB = 0x00;
  for (int i = 0; i < N_cycles; i++)
  {
    portvalue = 0;
    do
    {
      ASM_INC(portvalue);
      //add some assembly No OPerations to keep timing the same
      asm volatile ("NOP");
    }
    while (portvalue < 255);
  }
}