Distortion products

In a spectrum analyzer, there are nonlinearities which produce distortion products. Examples are harmonic distortion and third-order distortion. There are actually many orders of products, but usually second- and third-order are the most prominent. The following is an example of how a signal analyzer behaves. One key subject will be the ability to determine if the observed distortion is caused by the device under test or internally in the analyzer. Many times in making signal analyzer measurements there is a need to determine or separate internally (in the spectrum analyzer) generated distortions from those generated in the device under test. The input attenuator plays a large role in this task. In order to test for overload, it is necessary to increase the attenuator. If the displayed signal reads the same amplitude, there was no gain compression and it is safe to return to the original attenuation level. If, however, there is a difference, the attenuator should be once again increased until the level readings are constant. Gain compression or overload occurs when a large signal causes the measuring instrument to indicate a lower level than it should. In the case of distortion products these results are even more dramatic.