RFI is everywhere.
73,
Steve
NN4X
<http://www.strategypage.com/htmw/htecm/articles/20101209.aspx>
Crossed Signals
December 9, 2010: Recently residents of Bremerton, Washington State
(northwest U.S.) were warned they may have problems with wireless
electronics (especially garage door openers and keyless care remotes) as
the U.S. Navy tests electronic systems on the carrier USS Stennis. The
ship has undergone some refurbishment recently at a Bremerton shipyard,
and the electronic systems need some testing before the ship puts to sea.
This is not a new problem, which is why the navy put out a warning this
time. Six months ago, the U.S. held naval exercises off Hawaii. But
first, many of the ships involved tested electronics while docked,
before going to sea. That’s when all the reports came in about garage
door openers in the area not working. It was interference from the
military electronics. But no prior warning was put out. Someone should
have known better. Even new civilian broadcasting equipment can be a
problem. Late last year, U.S. military personnel and their families in
Japan were warned not to use a number of American wireless devices (baby
monitors, cordless phones and so on), because they use frequencies too
close to those allocated to cell phone service in Japan.
But it’s military electronics, which usually don’t operate near a lot of
civilians, that cause the most difficulties. This sort of thing can be
traced back to decisions made years ago, that have only recently turned
into a problem. For over half a century, one of the radio frequencies
reserved for military use in the United States (380-400 megahertz band),
was also used for some consumer electronics. Starting in the 1980s,
manufacturers of garage door openers were allowed to use the 390
megahertz frequency, because the openers were very short range (low
power) and unlikely to interfere with military radios (or vice versa).
But a new generation of military radios has changed all that, by sending
out a very powerful 390 megahertz signals. Six years ago, garage door
openers were sudden being activated by the new military radios in the
United States.
The problem first showed up as new military radios, using the 390
megahertz frequency, were installed on military bases. By now, most
bases are using the new radio system. While the Department of Defense
believed that the new radios only made garage door remote control
systems inoperable, thousands of users reported seeing garage doors open
and close by themselves. While the garage door system manufacturers were
using the 390 megahertz frequency unofficially (but with the knowledge
of the government), they had to change their equipment to use another
frequency. But before the gear using the military frequencies could be
replaced. Over 50 million garage door systems (those within 80
kilometers of a military base), were involved in the mysterious
malfunctions.
There are increasing problems like this, as more wireless equipment
comes into use, and the military makes more use of frequencies they have
long “owned” but not really worked hard. It's an old problem, and was
first noted on a large scale during the 1991 Gulf War. Here, there was a
large concentration of military equipment from all the American military
services, and foreign armed forces as well. There were several
unexpected incidents where frequencies collided in unexpected ways.
There was some of this again in Iraq after 2003. There will be more
conflicts like this, and some of it will be in combat, with deadly results.
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
|