Proprietary software can extend a wireless network range more than five times the current limit with the same equipment, the company behind it - start-up InspiAir - has claimed.

InspiAir has said it can make point-to-multipoint 802.11b Wi-Fi signals travel anywhere up to 5km using conventional 100mW transmitters. This is due to software-only change to 802.11b frames which improves signal quality but nevertheless leaves the signal comprehensible by unmodified clients, the company claimed.

As usual for such claims, the company will not discuss the actual technology, which it calls Virtual Transmission Manager (VTM), pointing to uninformative white papers. More unusually, the company has 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 e-mail 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 - without the need to use modems that cost €800."

In New York, Rick Kaminer of Multi-Media Communications, a service organisation building a public Wi-Fi network for the Hudson River Park, gives the same story. "I don't know how they do it, and they won't tell me, but 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 doesn't keep usage figures on the free Wi-Fi service which has been running since April - he believes the performance increase is due to antenna changes, combined with software to iron out interference problems.

"It's like lighting a match and seeing it a mile away. This does so much more, people don't believe it," said Kaminer, who also acts as an agent for Motorola wireless equipment, and plans to sell the InspiAir kit more widely. "I have a customer that wants to test it in Pennsylvania - I will refund his money if it doesn't work."

"We're a software company, not a hardware," said David Geller, a major investor in the company. "We work within the standard, to improve the range and quality of service." But he would not give details of the not-yet-patented technology.

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