Marki Microwave's Mixer Spurious Product Calculator App
Cool Product Report

Hyperlinks all around the Internet pointing to Hittite's infamous Mixer Spurious Product Calculator broke suddenly when Analog Devices swallowed up Hittite in 2014. The good news is that if you still want to use it, you can find it as the ADI Mixer-Spur Graphical Representation tool on the ADI website.

However, Marki Microwave now has a much nicer Spur Calculator that you will want to consider. It provides both a "Spur Web" format and a "Spectrum Analyzer" format for presenting mixer spurious products. The interface is very user friendly both for the input and the output specification.

The "Spur Web" screen uses a format pioneered by Collins Radio back in the middle of the last century that plots the RF/LO and IF/LO harmonics as straight lines, and then the user would draw a rectangle within them that represents the limits of the input and output frequency bands. Any spurious product lines that pass through the rectangle are inband at the output, and hence cannot be filtered out after the fact.

Marki's presentation does not draw a rectangle anywhere, but instead uses the user-defined input and output lower and upper frequency limits to bracket the Spur Web lines within the entire chart area. The disadvantage to this approach is that if you use the actual receiver operational input and output bandwidths for the simulator specifications, you do not get an appreciation for which spurs might lie just outside of the operational band. When you analyze spurious mixer products using a range of frequencies wider than actual operational band, you have to mentally construct the rectangle which defines the operational input and output band within the chart.

If that is a bit confusing, please take a look at the Spur Web display format that I implemented in my RF Workbench DOS-based software way back in the early 1990s (originally copyrighted with the USPTO under the name Tx/Rx Designer on 11/28/1994 - including the "Spur Web" moniker). In it, the defined receiver input and output frequencies are used to draw a rectangle within the plotted Spur Web in a manner that allows you to simultaneously see the spur products lines around it.

BTW, as far as I know I was the first person to dub the chart format as a "Spur Web," and I also believe mine was the first time that Spur Web chart format had ever been implemented in software with a graphical user interface. Tx/Rx Designer was truly ground-breaking in its day. RF Workbench is included in many collections of engineering software, including the "Engineering 2000" CD.

Here is an announcement for Tx/Rx Designer (the original for-sale name of the RF Workbench Shareware) in the August 1995 issue of the ARRL's QST magazine.

Posted December 1, 2017