The MSA as a
Filter Analyzer

Updated Dec 16, 2009

For a filter, normal Transmission mode graph will display the profile of the filter response. As in Spectrum Analyzer mode, the P+ and P- markers may be used to automatically locate peaks and valleys. In addition, there is a Filter Analysis feature available under the Analysis menu that opens the following window.

Filter Analysis. The Filter Analysis Function. a PDF file by Sam Wetterlin.



In this window, the user can turn filter analysis on or off, indicate what marker is to mark the peak, and also indicate the dB points to mark. Here we have marked that we want the points that are 3 dB down, and “-20” dB down. The dialog allows the dB values to be positive or negative, but always interprets them as being below the reference marker.


When OK is clicked, the MSA will place markers at the appropriate points on the graph.




In this case, markers 2 and 3 are placed at the -3dB points, and markers 4 and 5 are placed at the -20 dB points. If the scan continues, the position of the markers will be adjusted at the end of each scan. The marker data is displayed below the graph, and some additional data is displayed describing the filter characteristics: the bandwidth at -3 dB and -20 dB, Q, the shape factor (the ratio of the -20 dB and -3 dB bandwidths), and the ripple. The ripple is measured between the -3 dB points, and with such a nice rounded peak it is zero.