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6191Possible GPS Interference

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  • Sierra Rat
    Apr 16, 2011
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      I don't normally pass this kind of stuff on, but the following information came from a very reliable friend whose wife is a member of the search and rescue group in Plumas County.

      "For the emergency services community:

      Most emergency responders have a basic familiarity with GPS, and some use it almost daily. This satellite-based navigation system was originally developed for military use but very quickly became perhaps the most widely used civilian navigation tool since the compass. It is found in cell phones, hand held navigators, vehicle units, personal locator beacons (PLBs), boat and aircraft navigation systems, surveying equipment, etc. Of particular interest to emergency responders are situations where victims or other reporting parties use GPS to identify the location of an incident, and/or the responders use GPS to find the incident site, lay out a search grid, etc.

      Now picture the situation with GPS suddenly unavailable to you. No usable signal. Victims can't provide a geolocation, PLBs don't work, and you are back to map and compass for navigation.

      If that scenario bothers you, read on. This is the threat facing GPS in the United States, potentially starting later this year. And it's not a natural event, an accident or a terrorist action. It has to do with a private communications company and the Federal Communications Commission (FCC).

      First a little technical background. GPS signals are transmitted by a group of satellites circling the earth. They are actually very weak signals by the time they reach your receiver, which means that things work best when there isn't much electronic noise in the neighborhood of those signals. GPS transmitters operate in what is called L-band, a portion of the electromagnetic spectrum that is above 1500 MHz ( ... way above commercial radio, TV and emergency responder radio frequencies). Other activity in L-band has, to this point, been limited to relatively low power items, which avoids interference with GPS signals.

      That was true until recently. Then last autumn a company called LightSquared made an application to the FCC to start using high power transmitters in L-band as part of a wireless communications network. LightSquared's plans include the installation of some 40,000 high-power transmitters at frequencies just below the principal GPS frequencies. Given the obvious potential for interference with GPS, the logical approach would have been for the FCC to require analysis and testing to substantiate the company's assertion that there would be no problems with their proposal, but for reasons not fully understood, the FCC simply granted the company a waiver and allowed them to proceed while asking that they coordinate with other users of L-band to minimize impact. (That's a very brief summary of a rather long story.)

      I'm not one to start clanging alarm bells at the slightest provocation, but this situation is indeed alarming. Rather than inject personal opinion here, let me jot down some commentary from more educated people. I'll start by noting that GPS manufacturers, such as Garmin and Rockwell-Collins, have reacted promptly and loudly, indicating that the LightSquared plan will, without question, severely impact reception of GPS signals in both airborne and surface applications. Emeritus professor Bradford Parkinson of Stanford University summed it up with the following statement: "Effectively, the FCC is directing that a quiet-spectrum neighborhood be rezoned for concert rock bands at the threshold of pain. And LightSquared is suggesting that its current neighbors should simply add more insulation to their houses." He further points out that LightSquared's transmissions will be a billion times more powerful than GPS signals.

      The matter has been discussed in various trade journals and technical circles, but doesn't seem to have been picked up by much of the mainstream public media. Because of FCC's waiver approach, there is only a short time remaining for analysis, limited testing and other input on the plan before a final decision on implementing the whole thing. June 15 is a critical milestone, when a technical working group is required to submit its findings to the FCC. This would suggest that mid June is probably the cutoff for unsolicited public input as well."

      Also, here is a link, that seems to confirm this information.

      http://www.ligis.org/index2.php?option=com_content&do_pdf=1&id=121

      I'm not looking to cause a panic by anyone, I just thought our little group would like to be informed about this possibility.
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