Rabbit ears are multiplying.

Hit with rising cable bills and a weak economy, more Americans, especially young adults and lower-income families, are catching their shows using classic antennas.

Nearly 18 percent of all US households with TVs are watching old-fashioned broadcasts delivered for free over the airwaves, up from 15 percent of homes last year, according to research firm GfK Media.

That means 20.7 million homes, or roughly 54 million consumers, now get channels over the air instead of paying a monthly cable or satellite bill.

Despite all the talk about “cord cutting” and people watching shows online, this marks the first year since the recession that the firm has seen a notable uptick in broadcast-only viewers, as sustained unemployment takes a toll on household budgets.

From 2008 to 2010, 14 percent of the 114.7 million TV households were cable- and satellite-free. Last year, that figure ticked up by 1 percentage point. This year saw a 3 percentage-point gain.

“That really was a change,” David Tice, GfK senior vice president, told The Post. “I haven’t bought into the cord-cutting thing, but this was the first year we really saw a significant increase in the numbers of broadcast- only households.”

According to the study, 6 percent of TV households, or 6.9 million homes, canceled their cable service at some point in the past and now rely on free broadcasts.

GfK’s report also found that 16 percent of households downgraded TV service this year through March, while only 11 percent of TV households said they had increased service.

Some cable operators, such as Cablevision, have held the line on price increases. Meanwhile, Verizon took the opposite tack yesterday, saying it would raise prices for its FiOS TV and Internet service in return for faster connection speeds.

Tice also noted that people using Web-connected TV increased to 34 million households, or 29 percent — almost double the previous year’s 16 percent.