TB 9-6625-2188-35
10. Total Harmonic Distortion
a. Performance Check
NOTE
Keep cables as short as possible.
(1) Connect TI OUTPUT to notch filter input.
(2) Connect OUTPUT of notch filter to spectrum analyzer 1M Ω INPUT.
(3) Position TI controls as listed in (a) through (d) below:
(a) FREQUENCY Hz dial to 2.
(b) Frequency multiplier pushbutton to x10.
(c) OUTPUT LEVEL (dBm) to +10.
(d) OUTPUT LEVEL (dBm) CAL just out of detent.
(4) Position notch filter controls as listed in (a) through (d) below:
(a) NOTCH FREQUENCY switch to 20 Hz.
(b) ADJUST FOR NULL-COARSE and FINE controls centered.
(c) MODE push button to FLAT (out).
(d) ATTEN pushbutton to 0 dB (out).
(5) Adjust spectrum analyzer controls to display fundamental frequency of 20 Hz
and four harmonics.
(6) Set spectrum analyzer MARKER control to 20 Hz and record fundamental
frequency amplitude in dBm.
(7) Set notch filter MODE pushbutton to NOTCH (in).
(8) Record amplitude of 2d, 3d, 4th, and 5th harmonic as indicated on spectrum
analyzer.
(9) Subtract value recorded in (6) above from each harmonic value recorded in (8)
above and record.
Example:
2d harmonic = -91.5 - +26 = -117.5 dB
3d harmonic = -92.2 - +26 = -118.2 dB
4th harmonic = -98.5 - +26 = -124.5 dB
5th harmonic = -105.4 - +26 = -131.4 dB
(10) Add the notch filter test report correction factors from table 6 to total harmonic
values recorded in (9) above and record.
Example:
2d harmonic =
-117.5 +9.5 = -108.0
3d harmonic =
-118.2 +6.0 = -112.2
4th harmonic =
-124.5 +4.5 = -120.0
5th harmonic =
-131.4 +3.5 = -127.9
