Recently published test results by the Federal Aviation Administr...

laid out a waiver procedure for certain ultra-wideband devices, allowing existing GPRs and wall-imaging devices to continue to operate. Eligible users could keep operating those devices under Part 15 rules if they were purchased before July 15, 2002, and there continued to be no evidence of harmful interference. The FAA Technical Center in Atlantic City, at the request of the agency’s Office of Spectrum Policy & Management, conducted tests with such grandfathered GPR devices. Last year, the FAA said preliminary results pointed to very severe interference to airborne helicopters at a distance of 100 ft. from a GPR device. At the time, GPR proponents said those initial results appeared out of sync with how these devices actually operate because GPR emissions are required to be much lower than those from ordinary consumer devices such as laptop PCs (CD Feb 13 p1). The FAA tests were designed to assess the impact of GPR devices on aeronautical systems operating below 960 MHz. The tests showed that a GPR “exceeded the new FCC Part 15 requirements by as much as 12 db, caused severe interference in some scenarios to the FAA’s Air Traffic Control receivers making air to ground communications difficult, if not impossible, and interfered with the audio portion of airborne communications and NAVAIDS radios,” the report said. It recommended that FCC Part 15 regulations be changed to require that UWB testing use smaller spectrum analyzer bandwidths, perhaps in the 10 kHz range. It said that under such a scenario individual spectral lines that may cause interference would be visible on the analyzer. “These spectral lines are invaluable in assisting the FAA in making a determination [about] whether interference will occur,” it said. The FAA report also recommended that the FCC require GPRs to be shielded so emissions “other than those required for proper operation of the equipment” are suppressed. The report said this would direct the GPR signal more towards the ground and “thus lessen the effect on FAA systems.” The report noted that these test results can’t be used on their own to establish GPR interference criteria to aeronautical communications and navigation systems that provide critical safety-of-life systems. “These tests do, however, provide a qualitative demonstration of the potential for GPR devices to interfere with aeronautical systems. Although the GPR unit tested does not meet the requirements of FCC Part 15, it is one of the units waived by the FCC to allow for its operation,” the report said. It noted that because GPR interference mechanisms aren’t yet fully understood, the test results couldn’t be extrapolated to estimate the interference potential of a GPR that doesn’t meet Part 15 requirements. The report said FAA plans further testing of GPRs and other UWB equipment to characterize these interference issues.