Airwaves are needed for better wireless phone service.
The Federal Communication Commission’s latest airwave license auction wrapped up last week with wireless carriers and others bidding nearly $20 billion for the rights to spectrum currently in use by 175 television broadcast stations. But the federal agency charged with overseeing the nation’s spectrum use now has an even bigger task ahead: reassigning almost 1,000 TV stations nationwide that operate in the part of the UHF spectrum band being sold.
Why Are the TV Stations Being Moved?
The UHF spectrum band was established decades ago for television channels, with each station assigned six megahertz of airwaves within a total allocation of 228 megahertz. Almost 10 years ago, the FCC shifted the entire TV broadcast industry to digital technology that requires less spectrum per channel and can even allow two or more different stations to share a single channel assignment. With increasing demand for mobile phone service, and increasingly congested wireless networks, the agency realized that it could free up quite a bit of useful spectrum by squishing the existing station assignments into a much smaller amount of spectrum.
Why Do So Many Stations Have to Be Moved?
No broadcaster was forced to sell their license. In an initial round of bidding, UHF TV license owners wanted a total of $84 billion for all of their rights. But the wireless industry didn’t need that much new spectrum, and couldn’t have come close to the price broadcasters were seeking. Verizon vz and Sprint s didn’t buy any new licenses and AT&T t spent under $1 billion at the auction.
In the end, only 175 TV stations sold their licenses and will split about half of the auction’s $20 billion of proceeds. Of those stations, 12 are expected to simply go off the air, another 30 will shift to lower frequency VHF channels, and the rest are shifting to digitally sharing another station’s UHF spectrum.
But to give the wireless carriers large swathes of spectrum in the same frequency around the country, the FCC plans to free up airwaves that currently cover channels 37 and above in every market. That means that 957 stations which did not sell their licenses in the auction have to be moved to lower frequencies that are remaining assigned to UHF TV broadcasting. Congress allocated almost $2 billion to help pay for the moves, and the FCC has laid out a schedule to “repack” the nearly 1,000 channels to new frequencies over the next three years.
Still, broadcast experts say the timeline could be challenging to pull off. “The TV industry and its viewers are about to see a level of technical disruption that may be unprecedented,” lawyers at the firm Pillsbury Winthrop Shaw Pittman wrote in a blog post after the auction concluded. “It’s going to be a crazy time for TV stations.”
Get Data Sheet, Fortune’s technology newsletter.
What Do Viewers Have to Do to Watch Channels That are Moved?
The vast majority of viewers subscribe to a cable or satellite TV service. They won’t have to do anything because they get their TV channels via a wire or satellite broadcast that isn’t affected by the frequency swaps.
But millions of viewers, perhaps as many as one in five, still depend on an over-the-air antenna to get local TV channels. All channels converted to a digital format back in 2009, so over-the-air viewers should be able to continue to find channels that are moved through a process known as rescanning. Some digital TV and converter boxes automatically perform a periodic rescan, which checks all available frequencies for active channels, but other equipment must be triggered to rescan manually. The FCC has a web page with video instructions explaining how to rescan.
Will Viewers Need New Equipment?
Almost no one who watches over-the-air TV will need new equipment. In rare cases where a viewer has an antenna that only received UHF channels and a station they watch is shifting down to the VHF band, they would need to purchase a VHF-capable antenna.
But with so many stations needing to buy new transmission equipment as they shift frequencies, the transition may also speed the deployment of a new technology standard known as ATSC 3.0 that allows broadcasters to send programming in super high-definition 4K resolution. So far, the FCC says broadcasters who adopt ATSC 3.0, which would require that viewers purchase new equipment, continue to also broadcast in the basic ATSC 1.0 standard in use today.
When Will Wireless Carriers Get to Start Using the New Spectrum?
The FCC set out a 39-month transition schedule to move all the TV stations and get the spectrum into the hands of wireless carriers. But that doesn’t mean every YouTube googl and Snapchat-happy snap smartphone user will have to wait until 2020 for relief. Some TV stations and some local markets will complete the transition much sooner.
TV stations going dark will go off the air within 90 days of getting their auction winnings. And the very first phase of the channel transition shift is scheduled to be completed by November of next year.
Executives at T-Mobile tmus , which won the most new licenses at the auction, have said they expect to get some markets online this year. However, customers will also need new phones that are capable of using the new bands and those aren’t expected until the end of the year or in 2018.