General Operation 41
Harmonic Distortion measurement
If desired, IM distortion tests can be performed with only one frequency instead
of two. This turns the test into a simple harmonic distortion test. The only dif-
ference between this type of harmonic distortion test and the standard harmonic
distortion test is that the results are displayed as a line on the graph instead of
bars, and more frequencies can be measured than in the standard harmonic dis-
tortion measurement. See Section 2.5.1.2 for more details on harmonic distor-
tion.
Range of available frequencies
The range of frequencies available for the IM distortion sweep is dependent
upon the IM FREQ DIFF and the DIST SWEEP END settings. When the USER
LEVEL is set to EASY, the IM FREQ DIFF setting is available in the Coupler
Multicurve Advanced Menu. When the USER LEVEL is set to ADVANCED, the
IM FREQ DIFF and DIST SWEEP END settings are available in the Coupler
Multicurve Custom menu. See Section 2.3.2 for information on the USER
LEVEL setting.
The FP35 analyzer can produce signals and take measurements at 100 Hz inter-
vals between 200 Hz and 8000 Hz. Both the primary and secondary frequencies
used in the IM distortion measurement must be within this range. Therefore,
the beginning of the range is always IM FREQ DIFF + 200 Hz. The ending of
the range is always 8000 – IM FREQ DIFF, or DIST SWEEP END, whichever is
lower.
Example:
If IM FREQ DIFF is 1000 Hz, the primary frequency will have a range of 1200
Hz to 8000 Hz. The secondary frequency will have a range of 200 Hz to 7000 Hz.
If IM FREQ DIFF is 200 Hz, the primary frequency will have a range of 400 Hz
to 7000 Hz. The secondary frequency will have a range of 200 Hz to 7800 Hz.
If DIST SWEEP END is less than or equal to the first primary frequency, only
the primary frequency will be tested; there will be no IM distortion sweep.
The range for the static IM distortion test is IM FREQ DIFF + 200 Hz through
8000 – IM FREQ DIFF. The DIST SWEEP END setting has no effect on the static
IM measurement.
Frequencies measured for IM distortion
When performing an IM distortion sweep, the FP35 analyzer looks at frequen-
cies with a mathematical relationship to the primary frequencies of the test to
determine IM distortion. You can select which frequencies are examined by
using the DISTORTION selection in the Coupler menu. Use 2ND or 3RD for a
faster test. Use TOTAL for a longer, more complete test.
