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Test 2-9: Total Harmonic Distortion (cont’d)
Test Procedure
1. Reset the AFG:
*RST;*CLS Reset AFG and clear
status registers
2.
Set the AFG to output a sinewave with the 10 MHz filter enabled:
VOLT 24DBM Set AFG amplitude
OUTP:FILT:FREQ 10 MHZ Set filter to 10 MHz
OUTP:FILT ON Enable filter
INIT:IMM Initiate waveform
Perform steps 3 - 6 for each frequency listed in Table 2-9:
3. Set AFG output frequency:
FREQ <frequency> Set frequency
where <frequency> is the value specified in Table 2-9.
4. Set the Spectrum Analyzer center frequency to the output frequency
of the AFG. Measure the peak amplitude of the fundamental in dBm.
Note the result for use in step 6.
5. Set the Spectrum Analyzer center frequency to the second harmonic (
2 × fundamental frequency ). Measure the peak amplitude of the
second harmonic in dBm.
6. Repeat step 5 for third through ninth harmonics. Calculate total
harmonic distortion as shown below:
thd (dBc) = 20 ⋅ log
æ
è
√
result
2
2
+ result
3
2
+ … +result
9
2
ö
ø
where
result
n
(volts) = 10
[ (n
th
Harmonic (dBm) − Fundamental (dBm))/20 ]
Agilent E1445A Service Manual Verification Tests 65