Featured Product Archive
The inventions and products featured on these pages were chosen either for their
uniqueness in the RF engineering realm, or are simply awesome (or ridiculous) enough
to warrant an appearance.
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Hyperlinks all around the Internet pointing to Hittite's infamous
Mixer Spurious Product Calculator broke suddenly when
Analog Devices swallowed them up in 2014. For a while you could
find it as the ADI Mixer-Spur Graphical Representation tool on the ADI website,
but now it is gone, too, and even the
WaybackMachine does not have a capture of it.
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
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