Promotional still from the film Scanners. In case you didn’t get it.
As we all know, it’s necessary to scan for channels after setting up an antenna. That reads all the stations that the TV can receive and puts them in order into a menu you can access. But is there ever a reason to do it again?
First let’s talk about most TV tuners and converter boxes. When you scan for channels, you’re doing more than just reading frequencies. The PSIP system used for US television broadcasting contains information that lets your TV show that channel where you’re expecting to see it. When TV broadcasting moved from analog to digital in the mid-2000s a lot of stations changed broadcast frequencies. The programs that were once on channel 4 (for example) might now be found on channel 42. In order to make the whole transition friendlier, your TV reads PSIP data from the broadcast and puts channel 42 (again I’m just making an example here) on channel 4 so it’s easy for you to find.
Most broadcasters are done changing frequencies, but they may be adding or changing subchannels. Subchannels are the darlings of over-the-air enthusiasts; a single broadcast channel could contain three, six, or even ten distinct video streams, each shown on your TV as a separate tunable channel. These come and go with some regularity so you might consider doing a new channel scan every few months just to see what’s out there. You may find some new channels you like. Personally I just started watching a local feed of “Buzzr”, a network found only on a subchannel that carries old 1970s (and earlier) game shows.
If you have DIRECTV, things are even more complex. For reasons that have kept enthusiasts shaking their heads for close to a decade, DIRECTV does not actually use PSIP to show you guide data or channel lists. Instead they keep their own lookup table. Supposedly this was done so that each channel can carry the full two weeks of guide data that nearly every channel on DIRECTV carries. (The PSIP system usually only carries a few days of data.)
The big problem with DIRECTV’s system is that there’s a limit to how many channels it can store. The rumor is that only 50 channels can be stored in the table, including all subchannels. Unfortunately you can’t pick which 50 either. This isn’t a problem for many market but in the crowded large markets like New York and Los Angeles, many channels can be left out.
DIRECTV constantly tinkers with the table to try to provide the best possible experience. They don’t add or remove channels often, but again it’s not a bad idea to do a rescan every couple of months. If you’re looking for a particular channel to pop up, there’s a possibility a rescan will do that for you.
Personally I make a habit of rescanning every time there’s a change of season. Every three months is about right for me. There are rarely changes, but every so often I get a pleasant surprise.