VK3KHB

DiGiTaL TV Channels explained

---

Welcome,
the difference bewteen a Digital and a RF TV channel.
In the old TV system one TV channel equated to one RF "Radio Frequency". In the new system many TV channels share the one radio frequency. Many Digital TV channels effectively hide inside one RF TV channel. Below is a table of Melbourne's Digital TV channels as of May 2010, this list would apply to most Australian capital cities except for SBS as its RF TV channel number varies the most between capital cities. If you want more information see: wikipedia

Most of the above groupings are TV network based, Seven with 7Two, ABC with ABC1,2,3 and SBS with SBS1, SBS2 etc. makes sense, however it is what the other broadcasters do with their many TV channels you may find confusing...

Good confusing examples are TEN Digital with ONE HD and NINE with GO. Even more confusing is Nine's 3D TV test transmissions on a completly different DTV channel (40), streamed off RF channel 35. Its more confusing because Community TV C31 is on DTV channel 44, which is streaming off RF channel 32.

Under the analog "Free To Air" TV technology you have 1 channel per TV network. Under Digital you can have many channels per TV network. For branding purposes the TV marketeers are either pushing the digital stream number as the "channel" number or a "name". Conceivably the "name" can be transplanted to a different TV network if the need ever arises. While numbers will be forever tied to the respective network, names are not.

So what are all these numbers? (0 - ???)
"DTV Ch S#" is a number to identify the specific Digital TV Stream, which usually reflects the TV network identifier or a numeric group, this is usually set by the transmitting station and can be any number, even the same one in use by another TV network. However I suspect a "code of conduct" discourages the idea. Not all receivers (older ones) can decode / display this number and TV networks tend to use this number as their channel "brand" selector.

"RF Ch#" is the Radio Frequency free to air channel number (0 - 69) as set by Australian Communication & Media Authority and this is the real channel number you need to receive programs on.

Now this is where it can get confusing; a "channel" can refer to both a Radio Frequency channel (0-69) and a Digital stream channel ( 0 - 999+ ). The numeric overlap 0-69 and a misconception that every channel number has its own frequency number is where the confusion begins. Several DTV Channels or names can share one frequency, each TV station broadcasts what services are available under their respective RF channel. You get this information when you first set up your TV receiver, it scans all the TV bands as frequecies or channels to find the active TV stations. If the station is not sending or your reception is poor then your TV receiver can't find all the services, also some time after you've setup your TV receiver if the sending TV station changes or adds services your TV receiver may not know and another scan of the TV bands is necessary...

The 3D TV tests on DTV 40, most set top boxes may detect only an audio stream, no video, only the very latest digital receivers may see a twin video pictures.

The "TV Network" is the broadcaster's "brand / identity" which may change over time as networks sort out what things viewers want to watch and what advertisers or other entertainment providers see as worthwhile audiences to flog products and services to... You can expect more dubious programme content and having to retune / rescan your TV receiver every so often as the broadcasters jockey for audiences and market share.
Conceivably the FTA commercial TV networks of today may just become media carriers for other entertainment brands like on cable TV. Nine and TEN seems to be going down that path.

"Frequency" is the magic numbers you need to key in manually if your digital TV receiver fails to find all the free to air "TV network" channels.

How can it fail?
As digital signals are still carried by analog carrier wave all the propagation problems of fade, ghosting and interference still exist, except digital can recover quality video & audio from "poor" signals. (Hence digital aTV is possible with a very high gain TV setup). However, digital can not overcome signal level problems caused by ghosting, poor antenna or cable installations and it will only display if it can cleanly recover the video / audio, else you see a blank screen and / or silence. You may be changing a snowy ghosting picture for jittery blocky one or none at all. But be reassured though that a stronger signal will result in a better service so check those cables & get the antenna fixed / replaced.

Why is it so confusing?
It all relates to the technology and how we use it. We strive for simplicity and create complexity. Most TV receivers work all this channel numbering out for you and you simply see channel 0 - 999, but if your DTV receiver gets it wrong, your in trouble and need technical guidance...

History a brief technical explanation:
Analogue signals are made up of 1 video with 2 audio services. Analog has defined maximum levels for video & audio signals in an infinite series of complex level relationships which can and must exist to convey the picture and audio. All this complex signal information for just one TV channel needs to occupy about 6 - 7Mhz of bandwidth, refer to the PAL(B) TV format for more information. This 7Mhz bandwidth is superimposed on an analog carrier wave with a frequency set in 10's - 100's of Mhz (Megahertz). This bandwidth is grouped in to a channel, 0 to 69 and your PAL(B) TV receiver decodes the channel you select. The quality of that decoding depends on how well it can work out what the complex series of video and audio levels are from the received analog carrier wave signal.

Digital technology uses the same bandwidth but can fit several video and dozens of audio services in the same space as one analogue, which can all have different content and all be viewed at the same time. Digital encodes the complex series of infinite video and audio levels to several known or expected states, which your digital receiver can work out. The TV "smarts" have compressed that old analog signal to just one data stream the remaining bandwidth is now extra capacity for many more video / audio services.

So how do you select them?
To select a Digital TV stream of a particular Radio Frequency TV channel; you will need to choose it's matching DTV Channel Stream number. It is a channel number with-in a channel number and hence the confusion, especially the way some TV networks have branded their services. This confusion also extends to putting the same content on many of their other Digital TV S# channels. Understandably you don't want the duplicates and delete them, only to find out later that you need it, to view a repeat or a new or extended service that is now on offer (ie. Nine G0). You have to retune, loosing any saved programs or re-learning how to zip thru the channels again...

Programme content: The quality of programme content is not a result of the digital technology, that is related to commercial interests, control of programme materials by the media players and politicians setting laws on who can do what. Digital TV whether by free to air, cable or internet, will always deliver quality images and sound no matter how poor in taste the programme content is.

[ Please note: The amateur TV (aTV) service is an "out of normal TV band" service and a specific scan by frequency (not channel) must be done to add this experimental TV service to your receiver; which can only be included if the aTV service is transmitting and your TV antenna can collect enough of the low power signal. Some receivers do not cover or a very deaf at the aTV frequency, a very high gain UHF antenna or RF amplifier may be needed.]

I hope this helps you to understand some of the aspects of DiGiTaL TV and why it is not as straight forward as it could have been. The ever pressing need to make money from "what you like viewing" as entertainment or information will make life interesting, if not somewhat frustrating.