3 Making Measurements
Third-Order Intermodulation Distortion
Two- tone, third- order intermodulation distortion is a common test in communication systems. When two signals are present in a non- linear system, they may interact and create third- order intermodulation distortion (TOI) products that are located close to the original signals. System components such as amplifiers and mixers generates these distortion products.
In this example we test a device for third- order intermodulation using markers. Two sources are used, one set to 300 MHz and the other to 301 MHz.
1Connect the equipment as shown in figure below.
N9310A
7 
8 
9
4 
5 
6
1 
2 
3
0 
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Signal generator
Directional coupler
7 | 8 | 9 |
4 | 5 | 6 |
1 | 2 | 3 |
0 | · |
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Signal generator
This combination of signal generators, low pass filters, and directional coupler (used as a combiner) results in a two- tone source with very low intermodulation distortion.
Although the distortion from this setup may be better than the specified performance of the analyzer, it is useful for determining the TOI performance of the source/analyzer combination. After the performance of the source/analyzer combination has been verified, the DUT (Device under test, for example, an amplifier) would be inserted between the directional coupler output
40 | N9340A User’s Guide |
