In
less than a month and a half, standard analog broadcasts across the US will cease. However, not
all analog signals will cease. For example, if you are on cable systems, you will most likely still see analog for quite a while. If you are getting your signals over the air (meaning you use an antenna, not through a cable service provider or satellite dish), there are a couple of things to keep in mind:
- Channel Numbers: In the analog world, the channel number referred to the actual RF channel (a 6 MHz wide chunk of spectrum) that your TV used. For example, if you were watching channel 2, that meant that your TV was tuned to a signal residing between 54 - 60 MHz. Or perhaps you were watching channel 13, which referred to the spectrum between 210 - 216 MHz. Well, in the digital world, it's not that simple. As part of the digital bit stream coming into your digital-ready TV (or digital converter box), each channel is assigned a "virtual channel number". This may (or may not) be the same as the RF channel. Look at the image at left. This shows the RF channel number (27) and the assigned virtual channel number (26-1). Most likely, the virtual channel number applies to the station's analog channel number, which most people are used to.
- Multicasting: Notice how your digital channels are listed as "26.1" or "26-1"? That's because of something called "multicasting". That means that a TV station can put multiple programs onto one RF channel. For example, in the image shown, the channel is listed as "26-1". That's because it is the first program on the channel. But there are others. In this case, there were four programs running on this one RF channel. The first, listed as "26-1", was a program about home improvement. The second, third, and fourth programs (listed as "26-2", "26-3", and "26-4", of course), were a local program about Washington, DC, a cartoon, and a news program.
- RF Channels: The FCC first established 82 channels for analog television (channels 2- 83). In the 1980s, the top 14 channels (70 - 83) were given up for a new service called "cellular telephone". Now, with the transition to digital television, even more RF channels will be given up; channels 52 - 69, to be precise. Starting on 17 February, only RF channels 2 - 51 will be available for television. Those channels from 52 - 69 (a total of 108 MHz) will be used for new wireless services. But, in a practical sense, this also means that, if you already have a digital TV or converter box, you will need to re-scan on or near that date. That's because many stations will be changing frequencies. Your TV will need to know where to find them, requiring a rescan of the RF channels.
1 comment:
Ah, yes. A good description of digital TV to come. I note that the dates are being mucked about and this will no doubt cause some minor changes.
A minor comment or two. Digital is wonderful while there is adequate signal to process but it tends to be all or none and the artifacts of noise or signal losses are more noticeable. The old analog system didn’t cram as much into the available bandwidth but tended to more or less gracefully degrade as the signal levels dropped.
Having said this, I recently purchased an entry level digital signal box for off-air broadcasts while the condo association decides what they will do with the CATV antenna system. Not having added a switch between the current system and the digibox and its amplified panel antenna, I have to change the cabling manually.
In the mean, I’ve lost a few channels I used to watch but gained a few I did not have before. In particular, the four major broadcast stations Fox, ABC, CBS, and NBC remain about the same but their 2nd or 3rd channels now come through the digital side. The additional weather radar and such have not been all that useful but the one PBS station I get, of the three I had, actually has four channels of programming. So, even without cable, the adage of more channels and less to see remains intact.
Now, if they can actually get four worthwhile channels of programming into the RF spectrum allocated, then some conservation of the most expensive “real estate” in the world has been made and the reallocation of the frequencies released will have been wisely made.
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