Effective Intermodulation

Normal two-tone intermodulation performance assumes that

• the interfering tones are spaced at equal intervals from the desired signal, and

• the interfering tones are in the signal passband.

Filtering is often introduced to the system to reduce the interfering tones relative to the desired signal. Because of the filtering, input levels to subsequent devices are reduced, and, consequently, produce less intermodulation distortion in the final output. The net effect is to create an apparent IPx that is greater than the inherent IPx of the system without the filters (see effective intermodulation for more information). SysCalc uses a two-tone calculation with a default offset values of .025 MHz and .05 MHz, respectively.  If filters exist in the system that would appreciably attenuate these tones then the IM calculations will reflect this.  The solution is to change the tone spacing of the signals to be sufficiently in the signal passband.

1. Click on the Properties button on the Main Toolbar to invoke the Properties dialog box shown below.
2. Click on Project of interest within the tree control to select the project properties.
3. Click on the Source tab.
   
   
    
4. Change the IM Offset to an appropriate value
5. Click OK to close the dialog
6. Click Solve to update the system.