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168 Chapter 3
Programming Examples
Measuring Harmonic Distortion (GPIB)
viQueryf(viESA,"CALC:MARK:Y?\n","%1f", &fHarmV[lNum]);
/*Change the amplitude units to DBM */
viPrintf(viESA,"UNIT:POW DBM\n");
/* Read the marker amplitude */
viQueryf(viESA,"CALC:MARK:Y?\n","%1f", &fHarmDbm[lNum]);
}
/*Sum the square of each element in the fHarmV array. Then
calculate the relative amplitude of each harmonic relative
to the fundamental */
for (lNum=2;lNum<=lMaxHarmonic;lNum++)
{
dSumSquare= dSumSquare + (pow (double(fHarmV[lNum]) ,2.0));
/* Relative Amplitude */
fRelAmptd[lNum] = fHarmDbm[lNum] - fFundaAmptdDbm ;
}
/*Calculate the total harmonic distortion by dividing the square root of
the sum of the squares (dSumSquare) by the fundamental amplitude in Volts
(dFundaAmptdV).Multiply this value by 100 to obtain a result in percent*/
dPrcntDistort = ((sqrt(double (dSumSquare))) /dFundaAmptdV) *100 ;
/*Fundamental amplitude in dBm */
printf("\n\t Fundamental Amplitude: %lf dB \n\n",fFundaAmptdDbm);
/*Fundamental Frequency in MHz*/
printf("\t Fundamental Frequency is: %lf MHz \n\n",dFundamental/10e5);
/*Relative amplitude of each harmonic in dBc*/
for (lNum=2;lNum<=lMaxHarmonic;lNum++)
printf("\t Relative amplitude of Harmonic[%d]: %lf dBc
\n\n",lNum,fRelAmptd[lNum]);
/*Total harmonic distortion in percent*/
printf("\t Total Harmonic Distortion: %lf percent \n\n",dPrcntDistort);
/*Close the session*/
viClose(viESA);
viClose(defaultRM);
}