Whay aren’t cable TV chanel numbers the same as non-cable chanel numbers? And are satellite numbers also different?
In my cable box, they are.
A cable TV company actually ‘re-broadcasts’ the TV signals it receives over the cable that comes to you.
In other words, the cable company has a license that allows it to pick up various satellite feeds, local TV signals, or even (I guess) other cable feeds. It then takes each signal, and transmits that signal on one of the frequency bands available on it’s own cable. In doing that, it can choose to route any incoming signal onto any frequency band on it’s cable. A ‘channel’ is just a particular frequency band that is used to transmit a TV signal.
To avoid confusion, virtually all cable companies will choose to put (at least most of) the local stations on the same channel on the cable as that station is normally broadcast on. But they don’t have to (at least not for any technical reason, their contract with the local station may require it), it’s done for convenience.
All the other channels just need to get put on any unused channel on the cable. And they can move them around. At one time, it wasn’t unusual to find one channel which was a family or educational station during the day, and an old movie station at night. This let the cable company conserve bandwidth by getting dual use out of a single channel. And of course, it’s not unusual to have your cable company move the various stations to other cable channels, to make room for new channels, or to group like stations together, etc.
Your cable box then receives the station on whatever frequency band it is transmitted on, and converts that signal to the output channel, usually either 3 or 4, depending on which isn’t normally used in your area. So when you change the channel, you are actually selecting a different incoming frequency, which the box changes to channel 3 (or 4) which your TV then receives and displays.
And many cable boxes made in the last few years have a direct video output, which is a standard unmodulated video signal, just like your CamCorder or VCR can use. But the effect is the same, you select a channel, which picks a signal coming in on a particular frequency band, and the box converts that signal and sends it to the output that is hooked up to your TV or video controller.
Clear as mud?
Ugly
Politics plays a big part. In Chicago WPWR is broadcast ch 50. They went around and agreed to let cable companies use their signal in exchange for being put on channel 8.
Now broadcast channels 7 and 9 are the two biggies in Chicago. And since most VHF broadcast channels are on the same numbers as cable it is a HUGE advantage to be put between them. Thus channel 8.
WFLD broadcast 32 likes to be cable 12 as it close (the last number is TWO).
Research show that people still tend to surf lower channels be they broadcast or cable.
In some cases a broadcast station on channel 2 or 3 must be moved due to interference.
By 2008 when all the TV stations are due to sign off and become DTV stations with new channel numbers the whole thing will be either mute or more screwed up.
Cable companies receive channels from satellites. They then can modulate that signal to any channel they wish. Backwater Cable Company may put HBO on channel 2 on your cable box. Vancouver Cable may have LIFETIME on channel 2.
Off Air channels are now going digital as well. Local channels are brodcast via transmitters allowing you to receive them with an antenna or by setting your tv to HRC using its internal antenna. Cable Companies usually pull these stations in using antennas as well but has the ability to remodulate this signal - changing it from its original channel to any channel they wish.
Each cable company controls its own channel line-up. They have the ability to add and delete channels at will.
My local channel 20 is delivered by cable also on channel 20 and this is the only channel that works like this. All other local channels are mapped to different channels on cable.
I bought a surge protector for my home theatre stuff that included surge-protection on the antenna. When I used it, all was cool…except channel 20 which became very fuzzy. The problem was the surge protector, when I sent the cable feed straight into the tv, channel 20 was fine, But when I sent the feed though the surge protector, channel 20 fuzzed out.
I bought a monster cable surge protector. And this worked perfectly even for channel 20.
My guess as to what was happening is the the original surge protector had poor shielding. I was picking up channel 20 though the air and through the cable. The two signals were mixing and confusing my tv. Since the other local channels were mapped to different channels this didn’t happen. When I watched cable channel 7, for instance, I probably got some signal from broadcast channel 7, but the tv could reject this because the signals were different. But two copies of the same signal a few milliseconds out of sync was more that it could handle.
I am not an expert at video stuff, but this is my guess as to why channel companies remap channels.
The answer is really pretty simple (and yes, this is a WAG)
Channels 2-20, or so, are usually your broadcast, off the air stations that come with basic, basic cable.
Channels 20-35 are generally included in the step up from basic.
35-50 are the next level,
and 50+ is usually the premium channels.
Meanwhile the UHV-VHF spectrum goes from 2-72(I believe).
It’s simply not very organizationally good to have the broadcast channels scattered about while filling the gaps with other stations. It just makes more sense to bunch them up at the bottom of the dial.
When our cable system was installed back in the early 80’s, channels 10, 12 and 6 (the big three broadcast stations) were 16, 17, and 19, respectively. The 6, 10 and 12 on cable had a semi-broadcast of the broadcast 6, 10, and 12…you had wavy lines of broadcast 10 mixed in with the community access channel (the cable 10). According to the cable company, this was caused by inadequate sheilding on the cable lines, so they put channels that few people watched on the cable 6, 10 and 12.
It was only a few months ago when the whole town had fiber optic lines installed that they have put 6, 10, and 12 on 6, 10, and 12 on cable. And even now, cable 10 has wavy lines of broadcast 10 moving through it. Very annoying.
Like that’s going to clear things up…
Cable companies using CATV distribution amps have several choices They generally use a 750Mhz amp which can go up to channel 116.
The basic CATV channel ferquencies are-
SUB Band- 55.25 and below on the video carrier frequency.
LOW Band- Numeric 2-6
High Band- Numeric 7-13
Mid Band- Numeric 14-22
Super Band- 23-117
On these systems attenuation in the cable runs (length of cable, splitters in line, connections…etc.) deplete the signal stregth of the higher frequecy channels more than lower frequencies. At the end of a cable run channel 86 will have a lower signal stregth than channel 3. Equalizers and slope adjustments are used to balance this signal during the length of these runs. Lower channels are attenuated by the cable co so that all channels have the same signal strenth at the end of the run. In this type of system any channel can be remodulated of any other channel.
Forward communications to your cable box is usually right around 50.5Mhz. This signal is in the SUB band and it tells the cable box what type of channel line up it needs to program to. This is also used to tell the box what the date and time is as well as channel names. This is how cable thieves “reprogram” their terminal. By inserting a filter from 50.5-55.5 Mhz you can eliminate the cable companys forward “instructions” to your cable box. By using a box preprogrammed with all the channels you get free cable.
Some pay channels are put on lower frequency channels such as 2. This way the cable co can put an inline filter (a unit that blocks a range of frequecies) to block hbo from your house. These are usually hooked to the cable conection on the outside of your house. (in those locked plastic bozes)