Third Order Intermodulation Measurement (Toi) - HP 8590 E-Series User Manual

5. Read the measurement results in the upper left corner of the screen,
6. Press % AM ON OFF (OFF) to turn the measurement off.

Third Order Intermodulation Measurement (TOI)

Use the TO1 one-button measurement to make quick and easy intermodulation measurements
of microwave spectrum analyzers, mixers or converters. When the TO1 measurement is turned
on there must be four signals on the display, two test signals and their two associated distortion
products. All of the signals must have peaks greater than the peak excursion value. (The
default value for the peak excursion is 6 dB.) The two highest amplitude signals are assumed to
be the test signals for the third-order intercept measurement.
The spectrum analyzer computes and displays the third order intercept (TOI) of the displayed
signals, marking all four signals with arrows to confirm the correct signal selection. The
measurement updates at the end of every sweep, which enables real-time optimization of
devices or systems under test.
The third order intermodulation is calculated as follows:
TO1 =
where the frequency of distortion product A is:
Third Order Intercept:
Third order intercept is defined as the absolute power level at which the third-order distortion
products intercept the level of two equal level test signals. If the distortion products are due to
true third-order distortion, then the measurement result will be independent of the level of the
test signals.
The measurement algorithm used by TO1 ON OFF (see above equation) corrects for the two
test signals being different amplitudes. The result is a calculated value for the two test signals
being equal amplitude, and is independent of the absolute level of either test signal. In order
to minimize the measurement error, it is best to keep the test signals as close as possible to the
same level and to the top of the screen.
The TO1 measurement accuracy (assuming the measured signals are near the top of the display)
is typically about f 1.8 dB.
2
Making Measurements 4-41