A question in email came up on how to “append” a series of sweeps…measure, change a parameter, run another, and graph them all together. Since this response is picture-intensive, I’m posting it here instead of mail.
The main display doesn’t have this capability. But the Automated Measurements do. For example, Release 0.996 (out early next week) will have the AMP Frequency Response Chirp plugin ported from the QA401. Let’s say you wanted to sweep a narrow bandpass filter, and you aren’t sure what smoothing should be applied, or how the smoothing might impact the measurements. You could run a few acquisitions at different smoothing settings and compare visually.
Start by locating the plug-in you want from the Automated Test menu. Here we’ll use the new Freq Response Chirp plugin available starting in release 0.996:
Set the output level to -10 dBV. This means the Expo Chirp aka Chirp aka Swept Sine will be -10 dBV or 100 mV in amplitude. Specify 1 octave of smoothing. This means that for each point, you will average over one octave of data. So, the point at 1 kHz will be an average of all data from 750 Hz to 1.5 kHz (the math isn’t quite that clean, but for illustration purposes it’s close enough). Specify one octave smoothing, and give the series a description name. Make sure the QA402 is in loopback, and the press OK and the acquisition will run.
You should get a plot that looks as follows:
Run the same plug-in again. As a short-cut, the F3 key will run the last plug-in and remembers the last settings. Change the indicated parameters. Remember, for 1/2 octave smoothing, you specify 2 in the “Octaves Smoothing” parameters.
Run it again. This time, you’ll be greeted with a choice where you can add the new trace to an existing graph OR add it to a new graph. This is where you can stack up traces. Note too that the it’s asking which Graph Window to add it to. The “Graph 177” will match the title bar of the last window:
Now the graph appears as follows. Note we have two traces, but we can’t tell which is which.
If you want to rename the trace, you can select it in the Current Trace dropdown and then do Traces->Rename Trace:
But since we specified a series name, the name makes sense. But let’s change the color to green so we can distinguish the traces:
Now repeat several more times with different smoothing options until you feel like you have a good sense of the options. You can change limits on the graph and add a title:
And when you have the graph setup the way you like, Edit->Copy Bitmap will let you graph a graph at a fixed resolution to insert into a document. Or you could save the bitmap at its current size via File menu.
And the final graph appears as follows: