[ARRL-OK] ARRL Aiding Effort to Mitigate Repeater Interference to Military Radar s

[D C (Mac) Macdonald]

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ARRL Aiding Effort to Mitigate Repeater Interference to
Military Radars

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.