ARRL Aiding Effort to Mitigate Repeater Interference to Military Radars A PAVE PAWS radar facility. [US Air Force Photo]
NEWINGTON, CT, Apr 17, 2007 -- The ARRL has been working with the US Department of Defense to develop a plan to mitigate alleged interference from 70 cm ham radio repeaters to military radar systems on both coasts. Amateur Radio is secondary to government users from 420 to 450 MHz and must not interfere with primary users. Citing an increasing number of interference complaints, the US Air Force has asked the FCC to order dozens of repeater systems to either mitigate interference to the "PAVE PAWS" radars or shut down. The Commission has not yet responded. 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. ARRL Regulatory Information Specialist Dan Henderson, N1ND, stresses that the Defense Department acknowledges Amateur Radio's value in disasters and emergencies and is being extremely cooperative -- and a wholesale shutdown of US 70 cm Amateur Radio activity is not in the offing. "The ARRL Lab is working up calculations on each repeater system the Air Force has identified to determine where interference-mitigation techniques offer a reasonable chance of keeping the repeater on the air," Henderson says. "In order for the amateur community as a whole to succeed in this venture, it is going to require the cooperation of all affected repeater owners." A US Air Force contractor identified the problematic repeater systems last summer, but the situation didn't become critical until the Air Force contacted the FCC a month ago. ARRL officials met with Defense Department representatives in late March to discuss alleged interference to the PAVE PAWS radar sites, and this week 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). PAVE PAWS is a missile and satellite detection and tracking system, and its name is a half-acronym. "PAVE" is simply an Air Force program name. "PAWS" stands for "Phased Array Warning System." Although PAVE PAWS has been in existence since the late 1970s, the Cape Cod and Sacramento sites are the only remaining operational facilities in the US. 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. As a "first step" to mitigate the interference, the ARRL is recommending that all affected repeater owners reduce power -- possibly to as little as 5 W effective radiated power (ERP). "We understand the difficulty this may cause to owners and users," Henderson said, "but the alternative to operating with a smaller coverage area may be not operating at all." Amateur Radio stations already must abide by a maximum 50 W PEP power limitation in the areas around both Air Force facilities. Henderson says the League is still seeking further information on the problem. "Until the Defense Department accepts a mitigation plan, repeater owners should exercise patience," he cautioned. "Once the ARRL Lab has completed its propagation calculations, we will be in a better position to provide advice for specific repeaters on a case-by-case basis." Contact Dan Henderson, N1ND (860-594-0236), with specific questions or issues associated with this situation. __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
