WASHINGTON — Members of the Very Small Aperture Terminal (VSAT) satellite communications industry are worried that their ability to deliver services is being compromised by interference from new terrestrial-based applications.

If allowed to continue, the interference could cost satellite companies dearly in terms of revenue, industry representatives said.

The Global VSAT Forum, an international trade association based in Hertfordshire, U.K., held a held an emergency summit here Sept. 29 to discuss interference in the C-band portion of the radio spectrum from new and developmental terrestrial broadband services such as WiMax and Advanced International Mobile Telecommunications.

According to Global VSAT forum Secretary General David Hartshorn, the problem is especially acute in what is known as the extended C-band, which lies between 3.4 gigahertz and 3.7 gigahertz on the radio spectrum. If it continues, he said, satellite companies eventually will be unable to deliver voice, data and video services, particularly in developing countries.

The interference so far seems to be concentrated in Asia and Latin America, Hartshorn said, with the worst occurring in Hong Kong, Australia, Fiji and Indonesia. Satellite operators also are worried because more advanced wireless services are seeking permission to operate in the C-band, he said.

WiMax is particularly problematic, Hartshorn said, because its transmitters emit signals that reach outside its permitted usage areas, and satellite systems are particularly sensitive to such emissions.

Rob Kubik, director of the government relations office of Motorola Inc., the Schaumburg, Ill.-based consumer electronics giant, said such characterizations of WiMax transmitters are inaccurate and unhelpful . Kubik also serves as vice chair of the WiMax Forum, a Mountain View, Calif.-based industry group devoted to making sure WiMax equipment is interoperable.

“Has a WiMax system ever interfered with a satellite system?” Kubik said . “I have not heard of any case of that happening.”

Satellite companies tell a different story. Kalpak Gude, vice president of government and regulatory affairs at Intelsat of Bermuda, the world’s largest commercial satellite operator, said a wireless broadband service being tested in Bolivia around the time of the 2006 World Cup drew complaints from Intelsat customers about interference. In response, Bolivian regulatory authorities deferred a pending decision on whether to license the terrestrial service to a later date.

“Bolivia now has the question in front of them,” Gude said. “We hope that in other countries of the world, it doesn’t get that far.”

The C-band is particularly important to VSAT operators because signals in that frequency range are more robust than in other areas of the spectrum available for commercial use.

“The reliability of this band has been incredible, said Gude. “That is what makes this band different; that is what makes this band valuable and important.”

According to Gude, pushing satellite services out of the C-band to make room for WiMax is not an option because there is not enough room in the Ku-band, and Ka-band signals have reliability issues under certain conditions such as during rainstorms.

Resolving the interference problem through regulatory channels will be challenging for satellite operators because of the difficulty in pinning down exactly which wireless service is causing the problem, said Dick Tauber, chairman of the World Broadcasting Unions , a Toronto-based group of broadcasting unions dedicated to solving industry issues .

“I don’t know what you can do, or how you can identify this signal and point to any one piece of equipment and say, ‘That’s where the interference is coming from,’” Tauber said at the meeting.

One solution would be to create “exclusion zones” surrounding Earth stations in which competing signals would not be permitted, he said, adding that such zones would have to be very large in order to be effective. WiMax also could be moved to another portion of the radio spectrum, he said.

Kubik said the WiMax Forum is investigating other bands , but added that companies that have paid for the right to operate the C-band likely would be resistant to change.

Kubik said various WiMax services are undergoing trials worldwide.

“Is part of that testing looking at satellite-related issues? It’s a relevant question to ask,” Kubik said.