Q: Why are stations changing their call numbers?
A: Short answer: they are broadcasting in both analog and digital right now, and they can't broadcast both at the same channel number, so they have 'temporary' (also called 'virtual') channels until the conversion.
Digital transmitters are on UHF (14-69) channels. The analog transmitters are still taking up the old VHF channels (2-13) until analog shut off so the digitals have had to use channels in the UHF region so as not to interfere with analog transmissions. This will depend on the area where the viewer resides, of course. Analog stations may already be in the UHF region.
This can get confusing, because there is a way the digital tuners are smart enough read the 'temporary' UHF channels and make them look like VHF numbers. The reason they do this is so you get the message that you are seeing 'channel 5' news on 'channel 5.' The tuner does this automatically.
When the station stops broadcasting the analog signal, they will probably put the digital signal where the analog was - so your channel 5 news will continue to be on channel 5. You may not even notice the difference when the conversion happens.
If you do notice a difference after the conversion, it could be because a station has changed from VHF to UHF or vice-versa.
So, you might need a different antenna. There's more about that on the Step-by-step DTV page.
Here are a few excerpts from our DTV Conversion television program (parts 2 & 3) that discuss some of the details of this change:
(From Part 2)
Bill Hayes: Let’s talk a little bit about the digital television reception. Most television stations, the majority, have two channels assigned. One is the analog channel and one is the digital channel.
Most of the digital channels are in the UHF band and a few in the VHF band. When broadcasters shut off their analog channels, some of them will migrate off of the UHF service back to the VHF channels. Some will change channels entirely.
One of the concepts that’s important to grasp in all this is called virtual channels. Since there were two channels assigned, virtual channels were assigned so that you, the viewer, did not have to learn a whole bunch of new channels.
If you were used to watching a station on a certain channel even on the DTV tuner, you could tune to that channel and you could find it, even though it’s not the actual channel. The other part of it was that it let broadcasters keep their identity. Some broadcasters have a lot invested in how they are known and some of them use their channel numbers.
Virtual channels are kind of like call forwarding. You do the scan. The receiver establishes this connection. And when you call for that channel, that analog channel, if you will, on your DTV tuner, it knows you really need to go to this channel. That’s important to remember because after February 17, some broadcasters are going to change and go back to their channels.
The problem is that virtual channels are not really well known so that it makes it difficult for you to select an antenna because if the real channel is a low band VHF and the virtual channel is a UHF channel and they’re going to stay in UHF, a low band VHF antenna isn’t going to help you. So a little later in the show we’ll show you a Web site that will help you determine what the real channels you’re going to be receiving are and what antenna you need.
Another concept you need to grasp is scanning. Scanning is very important in digital because scanning is what determines the relationship between the actual channel and the virtual channel. When you first turned on your DTV tuner, if you’ve got one now or are going to get one, one of the first things it’s going to want to do is scan for channels.
After that process happens, it has established those relationships. However, on February 17, when all of this shuffling takes place, it’s real important that you scan again because some of those relationships are going to change and your DTV tuner won’t know it unless you scan for it. So remember, scan and rescan. It will help you receive digital television.
(From Part 3)
Gary Sgrignoli: Well, here’s the problem. It’s different before February 17th than after February 17th. Right now in Chicago we have channel 2 and 5 are analog, channel 2’s digital is next door on 3. Well, now I need one of these big antennas. I’ve had one, I thought I just put it up a few years ago until I looked at the receipt and found out it was 20 years ago. Time flies when you’re getting old, right?
So, the problem is if I were to buy an antenna for now I’d want to buy the big one. On the other hand, channel 2 and 5 analog, their digital is in UHF and they’re staying up there. And channel 3 is actually moving to channel 12. So, I like this channel 7 to channel 69 antenna and it’s a little smaller and, of course, it’s newer than 20 years.
Paul Yeager: And this is called the channel 7-69 high band VHF/UHF. So, Bill, what would be the application in Iowa for the second tower we have listed here?
Bill Hayes: A lot of it hinges on what happens in the area you live in. In the Cedar Rapids/Waterloo market I know that channel 2 is going back to their – is going to stay on the UHF channel. I don’t believe that there is any other low band VHFs in that market. So, in that particular case if all that’s there is high band VHF, channel 9 is going to go, I believe – I’m trying to remember who else is up there.
Paul Yeager: KWWL is channel 7, channel 9 KCRG and there’s a Fox station at 28.
Bill Hayes: Okay, so there you have stations that are either high band VHF or UHF. In that market then this is probably an appropriate antenna because you don’t need the – if you look at the all band antenna, the longest of the elements, you don’t need those because those are the low band VHF elements.
You can go with a shorter, smaller antenna. In other places, Des Moines is a good example – in Des Moines all of the VHF stations, including channel 5, are going back to their VHF channels. In this market, if channel 5 wasn’t going back to channel 5, that antenna would work as well. But since you have channel 5, that’s a low band VHF, you’re stuck with the larger antenna.