Hyperlinks all around the Internet pointing to Hittite's infamous Mixer Spurious Product
Calculator broke suddenly when
Devices swallowed up Hittite in 2014. The good news is that if you still want to
use it, you can find it as the
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
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"
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
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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