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Tough Computers for Electrically
Sensitive Environments
The increasing popularity of wireless
in commercial and health environments has created EMC challenges
for makers of mobile computing devices. WalkAbout Computers, one
of the leaders in this emerging industry, has relied on Silent to
rapidly resolve these technical hurdles.
WalkAbout's flagship product, the Hammerhead XRT, has been designed
to stand up to rough and tumble places such as warehouses, airports,
loading zones, construction sites as well as emergency medical teams
(EMTs) where it is not uncommon for the XRT to be dropped or kicked
about in the course of daily use. The XRT's rugged housing is so
well designed that it can withstand several tons of pressure and
absorb extreme shock without any damage or performance degradation.
In real world applications this means users can depend upon reliable,
seamless operation without data corruption. (Visit WalkAbout's website
at www.walkabout-comp.com
to see a video of a multi-ton truck rolling over the XRT).
The XRT features a CDMA modem which links to enterprise information
systems for real-time processing of job orders, inventory, shipping
and medical records. Users must have the freedom to move about,
so radiated emissions and RF immunity requirements are very stringent.
Emissions have to be extremely low in order to prevent disturbances
in to environments with sensitive electronics. And the machine is
expected to work flawlessly in harsh electromagnetic environments
such as electrical power stations.
When Ron Valli, Senior Architect of Design and Development at WalkAbout,
encountered radiated emissions beyond acceptable levels, he contacted
Lee Hill and Randal Vaughn of Silent. The XRT had to comply with
FCC and European Class B radiated emission requirements for shipment
to the US and Europe. Due to the complex nature of FCC and European
radio modem testing requirements, low RF emissions are essential
for achieving regulatory compliance as well as ensuring robust wireless
performance. No simple task for mobile PCs with 1 GHz clocks and
CDMA modems that operate at frequencies up to 1900 MHz.
Randal and Lee reviewed the entire system design and imported the
XRT design data into their PCB file viewer to get an interactive,
real time picture of all signal and power layers. The source of
the problem wasn'št immediately apparent, but after researching
and using a CDMA test station in their debug lab, within a few hours
Lee and Randal narrowed it down to issues associated with the modem
design and features. They replaced the radio and ran anechoic chamber
tests again but the problem still lingered. Further diagnostics
led them to investigate the electrical characteristics of the modem's
connector, integral shield, and physical attachment to the XRT.
In one test, they discovered that the modem mounting holes were
electrically floating from chassis, causing excessive emissions
when linked to the base station. The solution: a new radio with
different mounting characteristics.
Ron Valli has nothing but the highest praise for Lee and Randal.
"In addition to being talented engineers, Lee and Randal are gentlemen.
I was able to focus on my job while they worked collaboratively
with my staff to solve a difficult problem at a crucial juncture.
The XRT was shipped on time with a retrofit that was both cost-effective
and manufacturable. "
As rugged PCs find their way into more and more commercial applications,
Silent continues to advise WalkAbout on next generation design architectures.
"With SILENT'S help, the future is not so rough and tumble after
all", said Ron. "We have enlisted SILENT'S help for our next
generation wireless platform." WalkAbout will continue to service
these markets with the highest quality products and services that
make personal communications in tough environments practical and
affordable.
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