Just found this at AVweb: The GPS industry is warning that a proposed broadband Internet network could effectively jam GPS signals. Further, it says it has data showing that any of the anticipated 40,000 (yes, four zeroes) transmitters can make a Garmin 430 go dark at a range of five miles. GPS World calls the proposal by LightSquared "disastrous" and warns of major problems for all kinds of GPS-reliant devices. The publication says a study (PDF) by GPS-industry stakeholders, including Garmin, determined the LightSquared network "will create a disastrous interference problem for GPS receiver operation to the point where GPS receivers will cease to operate (complete loss of fix) when in the vicinity of these transmitters." That, says the report, "will deny GPS service over vast areas of the United States." The industry told the Federal Communications Commission of the potential problem but the FCC approved the multibillion-dollar effort, which will carry 4G broadband throughout the country. In a podcast interview with AVweb, LightSquared spokesman Jeff Carlisle said the broadband system won't affect properly filtered GPS devices and his company is both mandated (by the FCC) and anxious to work with the GPS industry to identify devices that might be affected. The issue is the carrier frequencies LightSquared intends to use. The transmitters will use the L Band 1 (1525 MHz—1559 MHz), which is right next door to where the GPS frequencies of 1559—1610 MHz work their navigation magic. The GPS industry study says a Garmin 430 starts feeling the interference at 13.76 miles and experiences a "loss of fix in open sky" at 5.3 miles. Carlisle said the researchers didn't use the same equipment it will be using on the transmitters and LightSquared is going to test GPS devices under actual conditions to determine which are actually affected. The testing should be finished by the end of June but there's no indication what might be involved in filtering the affected devices or what that might cost. There's also been no mention of the Air Force, which maintains the GPS system and relies heavily on it for a lot of its systems.