Garmin is standing by its position that a proposal to build a network of 40,000 broadband transmission towers around the U.S. could severely disrupt GPS service. As we reported last week, LightSquared has received conditional FCC approval to install the massive system to carry 4G signals, the conditions being that it restrict its signals to their assigned frequencies on the L Band 1 (1525 MHz1559 MHz) and test existing GPS devices to see what kind of interference the transmitters might cause. GPS uses the a frequency range of 1559-1610 MHz, which is right next to the LightSquared signal. Garmin's Jessica Myers told AVwebin a podcast interview that Garmin has done testing on its own and determined there's no practical way for the two systems to coexist.
Myers said even if the LightSquared signals stay within their boundaries, they will be so strong compared to the very low-power GPS signals that reach Earth from the satellites that the GPS equipment will simply be overwhelmed. She said it may be technically possible to build filters that will block the LightSquared signals but they would be cost-prohibitive. Myers said that because the transmitters are ground-based, the biggest impact on GPS will occur in critical phases of flight like approach. She also noted that there are millions of marine and auto GPS units that could be affected. LightSquared says Garmin's tests are suspect because it didn't use the actual equipment that will be installed on the broadband towers. Real-world testing is expected to begin this month.