ARRL, IARU Continue Push for Limits to 70-cm Spaceborne Radars

NEWINGTON, CT, Oct 9, 2002--A just-completed draft revision to an International Telecommunication Union (ITU) Recommendation could result in reining in the potential for interference to amateur and other services from synthetic aperture radars (SARS) on 70 cm. Agenda item 1.38 at World Radiocomunication Conference 2003 (WRC-03) will consider a request to allocate up to 6 MHz of spectrum for SARs in the band 420 to 470 MHz to be operated by the Earth Exploration Satellite Service (Active)--EESS-Active. At issue is whether the EESS allocation could be established without interfering with incumbent services, including radiolocation and amateur.

"ARRL will continue to oppose SARs operating in the most active portions of the amateur 70-cm band," said ARRL Technical Specialist Walt Ireland, WB7CSL. The spaceborne SARs would be used to measure soil moisture, tropical biomass and Antarctic ice thickness, and to document geological history and climate change. EESS proponents contend that the best center frequency to penetrate jungle or forest canopies is 435 MHz.

"There is some hype starting up at this late date that gives the impression that the sky is falling," Ireland said, referring to recent news reports in the Amateur Radio news media that, among other things, incorrectly claim that EESS proponents are seeking "exclusive use" of 430 to 440 MHz and that the EESS issue is a new one.

While some occasional interference from SARs to amateur systems would appear inevitable, Ireland said, efforts to minimize the impact of the EESS (Active) operations have been under way for several years. "Although the SAR interference criteria limitations in the revised Recommendation SA.1260 automatically would eliminate three of the SARs, amateurs can still expect to receive interference from some of the remaining SARs on a limited basis if WRC-03 allocates frequency spectrum between 420 and 440 MHz to EESS (Active)," he continued, "especially if the allocation is made primary." The revised draft would keep four of the proposed SARs and eliminate those with peak radiated power levels from 400 W to 10 kW--that is, average power levels above 25 W, he explained.

Work on the major rewrite to ITU Recommendation SA.1260, hammered out by ITU-Radio Sector Working Party 7C over the last several years, wrapped up October 4 following a weeklong meeting. The draft recommendation sets interference criteria limitations for SARs to be operated by EESS (Active) in the 70-cm Radiolocation and Amateur and Amateur-Satellite Services band. Ireland represented the ARRL on the US Delegation to ITU-Radio Sector WP 7C. Ken Pulfer, VE3PU, represented the International Amateur Radio Union (IARU). For the past two years, Pulfer has been chairing the drafting groups that worked on the revision and brought it to its present status--along the way incorporating protection of the amateurs.

The draft revision to ITU-R SA.1260, Feasibility of sharing between active spaceborne sensors and other services in the range 420-470 MHz, notes that amateur "weak-signal" operation, including moonbounce, are centered around 432 MHz and amateur-satellite operations--both uplink and downlink--are conducted in the band 435 to 438 MHz. SARS and the Amateur Service can coexist at 430 to 440 MHz "by taking appropriate technical and operational measures," the draft states. The Amateur Service is primary at 430 to 440 MHz in Region 1 and secondary in Regions 2 and 3, which includes the US.

An annex to the draft revision, Methodology for interference assessment and mitigation, concluded that it would be possible to reduce the average power flux-density (pfd) of the SARs to enhance their compatibility with other services. "Sensor transmitter power, antenna gain pattern, pulse width, pulse repetition frequency and chirp bandwidth (if frequency modulation is used) are all possible characteristics that can be adjusted to improve compatibility," the conclusion states.

"It should be remembered, however, that an ITU-R recommendation is just that--a recommendation, not a regulatory instrument," Ireland cautioned.

Ireland notes that 18 sharing or compatibility studies have been conducted during the past seven years--eight of them completed in the past two years. "ARRL and the IARU have actively participated in these studies and in US and ITU-R working parties and study groups," he pointed out.

During the Conference Preparatory Meeting next month as well as at WRC-03 next June in Geneva, the ARRL has pledged to maintain its stance against egregious interference from SARs to Amateur Radio. The US also has expressed opposition to SARs that could interfere with its radiolocation systems in the band.

Earlier this year, the FCC's WRC-03 Advisory Committee and the National Telecommunications and Information Administration's Radiocommunications Conference Subcommittee recommended no change to the Table of Allocations in the band 420 to 470 MHz as the US position. Both panels determined that SAR transmissions could periodically impact amateur reception and even held "the potential for significant interference."

"Although the US recommendation was to maintain the status quo in the band 'unless measures are in place to protect existing services,'" Ireland said, "SAR proponents are certainly working to get an allocation, whether it be primary or secondary."

A copy of the Draft Revision to Recommendation ITU-R SA.1260 is available on the ARRL Web site. (132,568 bytes, PDF file)

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