ARRL Submits Plan to Mitigate Interference to Military Radars

NEWINGTON, CT, May 11, 2007 --The ARRL has submitted an interference mitigation plan to the US Department of Defense (DoD) as part of an effort to resolve reported interference from dozens of 70 cm amateur repeaters to US military radar systems on both coasts. Since Amateur Radio is secondary to government users from 420 to 450 MHz, hams must not interfere with primary users and, under the rules, can be forced to cease operation. Earlier this year, the US Air Force asked the FCC to order dozens of repeater systems to either eliminate interference to its "PAVE PAWS" missile and satellite detection and tracking radars in Massachusetts and California or shut down.
"We are waiting the response of the DoD representative to the proposal and will continue to provide information as to its status when it becomes available," commented ARRL Regulatory Information Specialist Dan Henderson, N1ND. The interference mitigation plan has four primary steps.
All repeaters the DoD has identified as potential interference sources will immediately and temporarily reduce transmitter power output (TPO) to 5 W.
The ARRL will conduct Longley-Rice studies on each repeater system to determine what further mitigation techniques might apply to individual repeaters. These could include relocating the system, the use of directional antenna systems to create nulls towards the PAVE PAWS site, permanent power reductions or a combination of these techniques.
The DoD will review ARRL's studies to determine if the proposals will meet DoD's unspecified field strength requirements to mitigate the potential interference satisfactorily.
Once the DoD reviews and approves the proposals, the ARRL will provide the recommendations to respective repeater frequency coordinating groups and the FCC.
The situation affects 15 repeaters within less than 100 miles of Otis Air Force Base on Cape Cod, Massachusetts, and more than 100 repeaters within some 140 miles of Beale Air Force Base near Sacramento, California. PAVE PAWS facilities occupy essentially the entire 70 cm band -- one factor that makes mitigation difficult. Feeding upward of 1800 active antenna elements, the broadband radar transmitters emit an average power output of more than 145 kW.
Henderson says the two frequency coordinating organizations involved would be expected to disseminate individual mitigation strategies to applicable repeater owners and trustees. They, in turn, would be responsible for implementing the proposals or developing alternative proposals that protect the radar systems to the same extent as the mitigation strategy would.
Cooperation will be the key to a successful resolution of the situation, Henderson says. "Although ARRL has no means to compel compliance with the mitigation strategies, each repeater is absolutely obligated not to interfere with these radars," he emphasized. "Failure to implement the mitigation strategy or otherwise eliminate interference attributed to an individual repeater will result in immediate FCC action."
Henderson points out that the FCC is aware of and monitoring this situation and will act as necessary to protect the radars from interference. He stresses, however, that the US military is aware of the critical role Amateur Radio repeaters play in disasters and emergencies, and a wholesale shutdown of US 70 cm Amateur Radio activity is not under consideration.
A US Air Force contractor identified the allegedly problematic repeater systems last summer, but the situation didn't become critical until the Air Force contacted the FCC in March. ARRL officials met with Defense Department representatives later that month to discuss alleged interference to the PAVE PAWS radar sites, and last month Henderson contacted Amateur Radio frequency coordinating organizations in both affected areas -- the Northern Amateur Relay Council of California (NARCC) and the New England Spectrum Management Council (NESMC).
Contact Dan Henderson, N1ND (860-594-0236), with specific questions or issues associated with this situation.