TB 9-6695-288-35
(11) Record difference between amplitude recorded in (10) above and amplitude
recorded in (5) above. This is the third harmonic amplitude.
(12) Calculate total harmonic distortion using figure 4.
Example
If second harmonic in (9) above, is -110 dB and third harmonic
in (11) above is -114 dB, dB difference is -4 dB. In figure 4 this
intersects the curve at +1.5 level.
The total harmonic
distortion is the largest harmonic amplitude plus number
determined in figure 4, (-110 dB + 1.5 dB = -108.5 dB).
(13) Total harmonic distortion (THD) will be less than -93 dB.
(14) Repeat technique of (3) through (13) above for each setting listed in table 7.
THD will be within limits specified.
Test instrument
Calibration Fixture
Spectrum analyzer
THD specifications
NOTCH settings
(dB)
Center Frequency
switch settings
settings
SPAN settings
1.0 x 100
100 Hz
100 Hz
500 Hz
<-93
1.0 x 1K
1 kHz
1 kHz
5 kHz
<-93
1.0 x 10K
10 kHz
10 kHz
50 kHz
<-93
2.0 x 10K
20 kHz
20 kHz
100 kHz
<-93
5.0 x 10K
50 kHz
50 kHz
250 kHz
<-80
10.0 x 10K
100 kHz
100 kHz
500 kHz
<-65
13
