InspiAir has said it can make point-to-multipoint Wi-Fi industry-standard 802.11b signals travel anywhere up to 5km using conventional 100mW transmitters using software-only changes to 802.11b frames.

This improves signal quality but nevertheless leaves the signal comprehensible by unmodified clients, the company claimed. But it declined to discuss the actual technology involved, which it calls Virtual Transmission Manager (VTM). It does, however, have customers ready to go on record.

"The professors in Helsinki University said this is against the laws of physics," said Antti Tapio of OCP, a company installing a commercial metropolitan Wi-Fi network in the Finnish capital. "Now the system is working, they support me."

Tapio says his network covers several square miles with just fifteen nodes and will open to customers next month. He says he has delivered point-to-multipoint web and email services, to a normal laptop, over distances up to 7.4km.

"We will charge far less than our competitors," he said, explaining that the system is eight to 10 times cheaper than conventional Wi-Fi – even before considering the running costs of the reduced number of access points.

"Compare it to what WiMax is promising in five years time," he said. "We are there already."

In New York, Rick Kaminer of Multi-Media Communications (MMC), a service organisation building a public Wi-Fi network for the Hudson River Park, agreed. "The technology works," says Kaminer, whose network will cover the Park, a new public space on the shoreline of New York, and the largest open space development in Manhattan since the completion of Central Park.

MMC is using two nodes from InspiAir to cover three-quarters of a mile, which appears to beat the usually quoted figures of 25 to 50 nodes per square mile for mesh coverage. Kaminer said: "It's like lighting a match and seeing it a mile away."

"We're a software company, not a hardware one," said David Geller, an InspiAir investor. "We work within the standard, to improve the range and quality of service." But he would be drawn on details of the not-yet-patented technology.

The world record for unamplified Wi-Fi distance is currently 124.9 miles, using large dish antennas.