Coupler Measurements 71
3.5.3 Performing an IM Distortion Sweep
In the IM distortion sweep test, the FP35 analyzer produces a sweep of the two
frequency combination mentioned in the section above. This is similar to a nor-
mal pure-tone frequency sweep, but two frequencies are used at a time instead
of one at a time. The FP35 analyzer measures the IM distortion by looking at
frequencies that have a mathematical relationship to the primary frequencies.
Any amplitudes at those frequencies is considered IM distortion. The results are
displayed as a double wide line with a percentage scaling found on the right
side of the graph. See Section 2.5.2.2 for details.
1. Press [MENU] from the Coupler Multicurve screen to enter the local menu.
2. Use [∨, ∧] to select DISTORTION.
3. Use [<, >] to select the harmonics where the IM distortion will be mea-
sured. You can select the 2nd distortion, the 3rd distortion, or TOTAL,
which is all frequencies except the primary and secondary frequencies.
4. Make sure the REF MIC is OFF. Use the arrow keys to make this selection, if
necessary.
Figure 3.5.3—IM distortion sweep
5. Press [NEXT] to enter the Advanced menu.
6. Use [∨, ∧] to select IM FREQ DIFF.
7. Use [<, >] to select the fixed distance between the primary and secondary
frequencies used in the measurement. You can choose between no distance
(HARM) to 4000 Hz.
