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I
-
Third
Order
Intermodulation
Measurement
(TOI)
Use the
TO1
one-button measurement to make quick and easy inter-modulation
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 inter-modulation is calculated as follows:
TOI
=
2
X
Amp&ml
A
-
AmP~disto~tion
product A +
Amplsignal
B
2
where the frequency of distortion product A is:
FFldi~to&on
product
A
=
2
2
Freqsignal
A
-
Freqsignal
B
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
*
1.8
dB.
5-64