Spectrum Bridge, a company that lists licensed airwaves for sale, has raised $8.1 million in second-round funding from Espirito Santo Ventures, True Ventures, Telecommunications Development Fund, Milicom Venture Partners and its own founders.

Based in Lake Mary, Fla., the company launched its web site SpecEx.com in September, and already has 1,000 posted listings for licensed segments of the radio spectrum. About 100 buyers and sellers are registered on the site.

Spectrum Bridge previously raised $2 million in first-round funding last year.