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Input ports with components at multiple freqs in SPECTRASYS

Question asked by rrobbi on Sep 27, 2004
The attached example file demonstrates two different ways to have an input port produce a signal with two or more components at different frequencies.  The instructions that follow assume that you already have a system in a schematic and that you have added a system simulation to your workspace.

One method to create a port with signal components at different frequencies is to manually add more than one source to a port.  To do this you need to double click on the system simulation in the workspace window to bring up the "System Simulation Parameters" window.  Under the general tab there is a list of sources.  To add a new source, go to the first open row in the sources table and click on the add button.  This will bring up the "System Source Parameters" window.  Here you can specify the port and frequency among other things.  Choose the appropriate parameters for your signal and click OK.  You can repeat this process to add multiple sources at a port.  Just be sure that you use the same input port each time you add a signal.  At this point your composite simulation will show both components, but if you have added paths, you will get some errors.  These errors come up because there are components at more than one frequency and SPECTRASYS does not know which frequency to use as the channel frequency.  To solve this problem, click on the paths tab and fill in the "Channel Frequency at Start Node" column for the paths that start at your multi-source ports.  The frquency you enter here will define the desired channel for that path.  You can also add another path that has the same nodes but a different channel frequency.

Another method you can use is to add a signal and use the "Step and Repeat Signal" option.  From the System Source Parameters window, check the "Step and Repeat Signal" box and fill in the appropriate parameters for your signal.  This is an easy way to generate evenly spaced signals, but it gives you less control over the power level of each component.  You will also need to go to the paths tabs and specify the channel frequency when you use this method.

The attached file also has a parameter sweep that shows how you can use equations to maintain a harmonic relationship between two signal components as you sweep the fundamental frequency.