[RFI] Crossed Signals (news story)

[Steve Sacco NN4X]

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.