Numbers assigned to digital TV channels

Radio stations have never used arbitrarily-chosen channel numbers. FM goes by frequency, and AM by amplitude, plain and simple. But this thread isn’t about radio, it’s about television.

Analog television (at least in the US) has always assigned specific channel numbers to the frequency ranges. Sometimes they aren’t even in contiguous group, but the average person doesn’t need to know that. The important thing is that my tv set has a range of channel numbers that it can receive, and for each channel, the receiver knows what frequency to look at. Sometimes, especially in the pre-cable-tv days, and in non-metro areas, there could be many channels on which nothing is being broadcast, but the tv set didn’t care. It still knew which frequency is assigned to Channel 7, and it tunes to it, whether something’s being broadcast or not.

But in recent years, I’ve noticed a change. It seems that for many digital tv companies, the channel numbers are not simple integers any more. My mother’s cable system uses channel numbers like 14-1, 14-2, 15-1, 15-2, and so on. You can see an example of what I mean here. What is the point of this? Why not just number them with consecutive integers? Is there a significance that I don’t see?

[RANT] I have to admit, I’m not just curious. I don’t like this arrangement, because it means extra buttons to press on the remote control. They had to make a new “hyphen” button just for this! I think it might also make it harder to learn which station has which number. There must be some benefit to this craziness, and I want to know what it is. [/RANT]

The change you note came about with digital TV broadcasting. Each channel, 4, 7, 13 etc. still has an assigned frequency, but since it is a digital signal, there can be sub-channels - which are designated as 4.1, 4.2 (or with hyphens).

A hidef 1080 signal takes up most of a channel, but with compression you can fit in an additional 480 sub-channel or you might get four 480 signals to fit in a single channel.

those numbers 14-2 or 14.2 refer to the subchannel of a digital tv channel, in this case subchannel 2 of channel 14. if there is only one channel just the single number appears.

a tuner could increment through these. a tuner might also if you enter 14 it would give a 14.1 14.2 on the screen that you could move up or down to select and not need to enter all the numbers. i have a tuner which gives all choices in this fashion; so enter 3 would give 32.1 32.2 34.1 34.2 34.3, use arrow to select.

both AM and FM go by frequency and there are even channel numbers for FM that are not used for tuning but assigned for allocations.

You both seem to be saying that 4.1 and 4.2 are using frequencies close to the frequency the Channel 4 uses. That sounds similar to what I remember hearing about HD Radio. But that seems useful only for a broadcast. I don’t see the relevance in a closed system like cable tv. Can’t the cable company use any frequency system they want, as long as the cable boxes are all compatible?

Digital channels can actually be multiplexed into the same frequency band, so 4-1 and 4-2 would use the same frequency.

If you are using a cable-supplied converter box, you will probably not be seeing those fractional or decimal numbers, but a 1,2 or 3 digit number from 2 (1?) to 999. At least that’s the way Charter Communications does it.

One advantage of the converter box to the consumer is that the channel numbers will always be correct even if the actual frequency changes; translation is done invisibly.

Charter subscribers without converter boxes have awakened some mornings and found that the channel they want to watch appears to be gone. The smarter ones will re-scan their TV and if they are diligent enough to click on all 998 possibilities, find the missing channel someplace else, like 12-9. Calls to tech support will be futile, because neither the customers or the customers’ agents are ever notified of these changes before or after.

Charter’s brilliant solution is to rent you a box at \$7 per month, per set. In my area, that is an option until April of this year, when your choice of going without will no longer be available and a box will be mandatory.

They do if you have a converter box.

I’m on comcast and we DO have a single integer system. So it is possible. However, it has a few annoyances [ul]
[li]Biggest of these is that the SD, HD, and spanish versions of a channel are 3 different numbers, usually with no logical correleation, except for the dozen or so broadcast networks (i.e. abc is at SD on 4, and HD on 104). [/li]
[li]Also, with the hyphen system, you can have different feeds (other shows from that network, censored/uncensored versions, etc.) in the same channel. With a single integer you have to know where the alternate feeds are, and they take up additional channel numbers (which are not unlimited).[/li][/ul]
As for remembering which network is on which channel, each network **should **have it’s own master channel (the part before the hyphen), with the subchannels being alternate feeds of that same content (as I described in the previous paragraph).

The extra button should also be irrelevant most of the time as the default subchannel (what you get if you don’t specify a subchannel number) should be the standard def, english (or whatever the dominant language of your region is) version. Basically, what you’d get before the digital switch.

It’s very easy to fall into the “the grass is always greener other side” trap. Unfortunately, the grass is pretty shitty* over here, too.

*as in brown like feces, not covered in manure (which is generally an excellent fertilizer)

Thank you, Musicat. I have a digital cable box, and all the numbers are consecutive. I have a relative whose system uses the hyphens, but she has no cable box, just a digital tv, so I guess it makes sense. Does this mean that the cable companies now have TWO channel guides, one for people with a box and one for digital tvs?

all over the air tv channels are assigned a frequency with a bandwidth (think of it as a container for data). a station can send high definition data using the full container (you can see nose hairs). a station can split that container and send a couple good quality signals; think of a tv channel and a channel that shows retro tv shows or a weather channel or both.

so 4, 4.1, 4.2, 4.3 are all in the same frequency block.

when a cable system might get signals from an over the air tv station they will report the 4.3 subchannel to make tv program listings still be useful but you might use the number 1134 to get to it. cable systems will provide a tuning chart to correlate channel numbers.

Your description matches my experience exactly.

I can’t speak for other cable companies; my only experience is with Charter.

The non-converter box, digital TV numbers (fractional or decimal) are not acknowledged, supported or recognized by Charter’s consumer agents. Whether that’s ignorance or company training, I don’t know. A lot of frustrated consumers bite the bullet and rent a box, so perhaps the “ignorance” is deliberate.

I have used computer-interfaced TV tuners, and they don’t use channel numbers, but true frequencies, which makes the whole thing an even worse mess, since the frequencies are subject to change without notice at any time, and frequently are. Charter doesn’t publish a list of the frequencies vs. numbers.

So Charter’s literature and on-screen schedule only mentions the 2…999 numbers and all other users are tuning at their own risk.

From a consumer’s point of view, it’s a sad way to run a company, no?

the channel numbers will be the same. you will only get the digitally encoded channels using the digital cable box.

if you look in your channel guide you will find for example; a local NBC station with an over the air channel number of 36, you and your mom might see it on channel 9 on cable, you might see a high quality digital picture on channel 867. your mom can only it on channel 9, if you flip between 9 and 867 you will see the same program with a massive quality difference.

No, AM goes by frequency too, it just uses lower frequencies. /nitpick

Thanks, all. It now makes a lot more sense. (Except for Musicat’s crappy customer service problems. My sympathies!)

Not correct, for now. I have two digital TVs and I get the digital channels just fine, but the numbers are wonky, and may change as I described earlier.

The digital cable box will be necessary in my area only when Charter scrambles all signals and removes all analog ones starting April. I understand other companies have done this already and eventually all of them will.

Just for the record, in the United States the FCC assigns channel numbers to the FM broadcast stations. Channel 200 is 87.9 MHz, channel 201 is 88.1 MHz, and so on. I do not know why the channel numbering system never caught on with the public or the industry.

TV channels do not operate in a single frequency notch like radio does, but rather they use a band width of frequencies, to carry both audio and video with different precise frequencies. The usable VHF part of the spectrum was allocated into 13 divisions, with each one using a wide swath of the band, designated as channels 2-13, with the band intermediate between channels 6 and 7 being allocated for FM audio.

If your old-time TV had a continuous, rather than slot, tuner, you’d have been able to hear FM radio in the space between channels 6 and 7,

TV and radio both use a range. For example, FM 89.1 really is allocated 89.0 to 89.2. Television is all 6 megahertz wide. For example, channel 20 (over the air TV) uses 506-512 mHz. But that’s 20.1 multiplexed with 20.2 and all the 20.x subchannels. The digital bits tell the TV which bits are for 20.1 and which bits are for 20.2. With digital TV, bits are bits. The video and audio bits are interleaved. They don’t use different frequencies for video and audio.

Now, to confuse matters more, the bits contained in the data tell the television the virtual channel. For example, here in Boston virtual channel 5 really broadcasts on RF channel 20 (506-512 mHz). The bits in the data tell the TV to “fake it”. Although the bits are coming in on channel 20, the TV tells the viewer that it’s channel 5.

I thought analog TV audio was amplitude modulated.

the audio is/was FM.

Did it have less bandwidth than FM radio? My Father was an engineer at the local NBC affiliate, and told me “TV audio was treated like AM radio”. I was pretty small, perhaps I disremember.