Message-ID: <005201c1def0$3d247000$a1f78a90@direcpc.com>
From: "Fred Moreno" <FredMoreno@bigpond.com>
To: "Lancair list" <Lancair.list@olsusa.com>
Subject: Electronic Interference
Date: Mon, 8 Apr 2002 19:22:06 +0800
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I also feel compelled to jump in to the discussion about the Ritchie
compass and electronic interference.  First off, I am not familiar with
the Ritchie compass.  But in my last job our company was responsible for
upgrading our equipment to meet European Community safety standards
which included testing in noisy environments - radio frequencies and
otherwise.  The requirement is that the equipment must operate safely
when bombarded by fairly strong and broadband signals that could
originate from any source.

What we found was many of our products that had been produced and
operated reliably for years went ape in the test cells, and major
efforts were required in the form of shielding and the addition of
special components to either drain off the stray energy, block it from
entering circuits, or both.  Sometimes more extensive changes were
required to withstand the test conditions which mimic the worst parts of
the real world plus some safety margin.  It's a very noisy world out
there, and your electronics can get deafened and maddened (and
surprised) by what they hear.

The problems with interference are growing as semiconductor circuits
mature.  In particular, many chips are now being made with much smaller
feature sizes so that more can be crammed onto a silicon wafer, thus
reducing cost.  This results (frequently) in lower operating voltages,
but also greater sensitivity to noise inputs.  Thus some of the new
devices are wonderfully capable when properly used, but if not protected
from spurious electronic noise from the surrounding environment, they
can be jammed the same way you can jam a simple radar - flood the input
stage with enough noise and the receiver loses its ability to detect and
process signal.  In the case of logic devices operating at low voltages
and high frequencies, the results can be especially unpredictable.

The trend is that we can expect modern electronic devices (bare,
unprotected) to become more and more sensitive to noise, and thus it
becomes more and more important to protect these components with
blocking and filtering devices capable of operating over a wide range of
conditions.  We used to joke that the threat environment was "DC to
daylight" meaning signals at all wavelengths from the longest to the
shortest.

So while we are the beneficiaries of better and more capable electronic
devices available at lower and lower prices, if they are not properly
shielded and defended against noisy environments (like airplanes
bristling with transmitters), one can expect reliability problems if the
proper design considerations were not included in the system
architecture.

Sadly, Hamid only speaks the truth.  With more and more delicate chips
and more and more noise in the environment (radios, cell phones,
satellite phones, and on and on) it is getting tougher and tougher to
design systems that will be absolutely reliable in difficult operating
environments.   It is sad because it makes it much more difficult for
the garage entrepreneur to produce a reliable and satisfactory product.

Fred Moreno

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