Looking at the Carrier Array Generation

This is for an Analog Devices Sharc processor

The stereo MPX relies on two carriers, the pilot at 19KHz and a sub-carrier of 38KHz. Thses are generated using arrays of samples. Thus there is complete control of the both the pilot and subcarrier phase modulation with respect to the baseband signal.

The Carrier Arrays

The samples calculation is very simple: 

                
int i;
float	mref19;
float	mref1;
float	mref2;
float 	m19;
float	c19 = 0.6217735;	//	Pilot increment angle per sample
float	r19;
m19 = 10.0 * pilot_level;
r19 = 525.0 * pilot_level;	//	The RDS level should be near the DAC maximum
//	This value should give 2.5v +- 2v. ie 4v peak-peak
for(i = 0; i < 192; i++)
{
	mref19 = ((float)i) * c19;				//	The phase angle
	mod_buf[i] = m19 * sinf(mref19);		//	The pilot
	mod38_buf[i] = sinf(2.0 * mref19);		//	The 38KHz
	if(bPilot) modaux_buf[i] = 7.5 * mod_buf[i];	//	Copy of pilot
//		else modaux_buf[i] = r19 * sinf(3.0 * mref19);	//	The 57KHz
	else modaux_buf[i] = r19 * sinf(mref19 - 48*c19);	//	The 19KHz phase shift
}

A pilot increment is calculated as the phase jump between samples. Then the carrier array are the iterative count of this, with the subcarrier incrementing twice the pilot. There some scaling factors to get the output levels correct, but note: these are equipment design dependent!

The possiblity of introducing a 57KHz carrier or phase offset pilot is shown.

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