Cable cord-cutting may be a real phenomenon after all. For the first time in four years there’s been an increase in the number of homes that just rely on antennas to receive programs from local broadcast stations according to research firm Knowledge Networks’ 2011 Ownership Survey and Trend Report. A survey of 3,343 people in March and April found that 15% of all homes now just depend on free TV, up from 14%. That puts the total number of broadcast-only viewers at 45.6 million people, up from 42 million last year. Knowledge Networks says that about 30% of the free-TV homes are pay TV cord cutters. Most said that they cancelled their cable, satellite, or telco TV subscriptions because they wanted to save money.

Although the increase in free TV use is small, the fact that it grew at all could frighten some investors. A 1% drop in the number of pay TV subscribers would shave about 1% off the market value of the largest cable programmers including Time Warner, Viacom, Disney, News Corp, and CBS analyst Laura Martin of Needham & Co estimated last year. Pay TV companies struggled for more than a year to reassure Wall Street that there’s nothing to fear. Cord cutting concerns diminished at the end of the first quarter when cable, satellite and telco TV companies reported a slight uptick in their total subscribers.

The new figures also could complicate the Obama administration’s effort to promote wireless broadband. The FCC has pointed to the declining use of over-the-air TV to justify its effort to coax broadcasters to give up airwave spectrum so it can be used to send data to smartphones, iPads, and other mobile devices. Last week the Consumer Electronics Association, which supports the administration’s campaign, released a survey it took in December that said just 9% of all households strictly rely on free TV. Curiously, the trade group said that “Americans are not rushing to cancel pay TV services” because 76% said that they were “unlikely” to cut the cord within a year. The more telling statistic: 10% said that they were “likely” to do so and another 14% were on the fence.