Dish Network Chairman Charlie Ergen is staying quiet on speculation that the company has become a major investor in Clearwire.

The rumors were sparked by a disclosure in a Wednesday securities filing that Dish had invested about $400 million in a "single issuer... [that] will need substantial additional capital to meet its business and financial obligations beyond the next 12 months."

That single issue may be Clearwire, Wells Fargo analyst Jennifer Fritzsche reportedly said.

Clearwire, which has frequently turned to investors for investment financing to keep itself afloat, said during its recent earnings call that it has enough cash to fund its operations for "at least the next 12 months." 

"We don't give disclosure on our strategic investments in terms of names," Ergen said during Dish Network's earnings call yesterday. "It's nothing unusual for us to be at that kind of level in a strategic investment from time to time."

Representatives for Clearwire and Dish Network declined to comment further on the issue.

Despite the lack of official confirmation, investors appeared optimistic about Dish Network's potential investment in Clearwire. Speculation over the cash influx sent Clearwire's stock soaring 18.5 percent by the end of trading Wednesday.

Clearwire holds a considerable 160 MHz of spectrum in the 2.6 GHz band in the country's top 100 markets and could be a valuable partner to Dish Network as it prepares to embark on the construction of an LTE network. Clearwire currently operates a WiMAX network and is building a TD-LTE network it plans to sell to other operators looking to supplement capacity. Sprint and Leap Wireless International have already signed up for the wholesale LTE service.

Clearwire President and CEO Erik Prusch said during its July 26 earnings call that it was in "active discussions with various parties who are interested in leveraging our assets.” He also said Clearwire was looking at “strategic” transactions with companies interested in more than just a straight wholesale agreement. Such a deal could include both an equity investment and access to Clearwire’s LTE or WiMAX networks.

Dish Network is waiting for FCC approval to use 40 MHz of satellite spectrum it holds in the 2 GHz AWS-4 band for a land-based LTE network. If the FCC grants Dish the required waiver, it will pave the way for the company to become a competitor to incumbent operators such as AT&T and Verizon Wireless.

Dish purchased its spectrum licenses through its acquisition of bankrupt satellite companies TerreStar and DBSD, transactions that closed this spring.

Ergen called the FCC's process for granted its waiver "frustratingly slow. But we're not the only people that have had government be slow."

Some in the wireless industry have petitioned the government to make Dish give up some of its spectrum. T-Mobile USA and MetroPCS asked the FCC in May to force Dish to give up half its spectrum in exchange for a waiver for its wireless service.

The request reflected the industry's need for additional spectrum and persistent rumors that Dish is not sincere about its wireless plans, and only wants the waiver to increase the resale value of its licenses. The FCC has proposed strict buildout requirements for Dish Network's LTE network, requirements Dish has sought to loosen.