When we consider buying a TV Tuner for our PC we see terms like NTSC, ATSC and PAL. What do these terms mean? What type of tuner do I want? What is a dual tuner? What countries have what signal? Do I get HD? Why did my picture not go to HD after the digital transition. What is Switched Digital Video? If you have had these questions check out this article!
This article is based on the outline I created for BYOB Podcast Episode 13. I have added some pictures and additional information as it applies to this post.
Analog Signal – NTSC
Most countries still run analog signal. When we talk about analog, you talk about SD signal. Worldwide, you are talking about NTSC, PAL or SECAM signals in countries broadcasting up to 576 lines. For standard definition in a standard 4:3 aspect ratio, NTSC countries are 640 x 480 while PAL countries are in 720 x 576.
This analog signal is the variable amplitude continuous signal with which most of us grew up. I am not going to get into the details, but NTSC, PAL and SECAM are analog. Analog is only SD and since HD signal cannot be transmitted over analog, many countries are converting. While the majority countries still offer analog signal, most developed countries are in the process of converting to digital. Canada should be digital by 2011 and the UK completed in stages by 2012. As for us here in the United States, there are some low power stations out there still in analog but all of the high power OTA broadcasting was converted to digital in 2009.
Digital Signal – ATSC
Digital signal is separated into HD and SD signal also know as High Definition (HD) and Standard Definition (SD). The resolution is what determines this format. Resolution is measured by the vertical lines, so 1080 is actually 1920 x 1080 and 720 is 1280 x 720. Standard definition also exists in digital form in 704 x 480, 720 x 576 or 640 x 480. Just because the signal is digital does NOT mean it is HD.
Although most of the rest of the world is slowly converting from analog, they do have other digital formats. Whilst the United States has ATSC, my brother Andrew Edney in the UK gets channels that are in DVB-T. South America has ISDB-T and China has DMB-T/H.
So what is digital signal? It is a transmission of information. For example, in North America, this transmission of data is up to 19 megabits (2.375 megabytes) from a broadcaster. Now, the broadcasters do not need all of this bandwidth for one HD channel so sometimes they put SD channels out within the same bit rate. For example, in Los Angeles, our NBS channel is 4.1 and they have enough bandwidth for a SD 4.2 and a 4.3 channel. We call this multiplexing. This special type of service is available since digital signal takes up less bandwidth.
Just like always, an antenna then receives this digital signal and then your digital TV tuner decodes the signals and shows you Dancing with the Stars.
Not all antennas are created equal. You can find all shapes and sizes that will fit your application.
Go to this site for really great information on antennas and signal strength in your area.
Now, you may also get your TV signal from a cable provider or a satellite dish. Digital cable is a different beast. Up until 1989, the cable companies were supplying analog signal. Motorola changed all of that by creating the digital signal for cable. This was a great advancement for cable. As I mentioned before analog takes up much more bandwidth than digital signal. In fact, the cable companies are now getting about 10 SD digital channels in the same space of one old analog channel.
Therefore, once Motorola showed they could convert analog to digital, the cable companies created a completely new set of digital services. Services such as telephone, internet, PPV and interactive menus were all now possible with digital cable. As I said before, you can only get HD with digital, so the old analog cable was SD. Think of this concept kind of like a plate on your kitchen counter. If you were to place a bunch of marbles, or analog signals, on top on the plate, you would maybe fit a couple hundred marbles right? Now, get rid of most of the marbles and use BB’s, which represent the digital signal, and you can fit thousands. In fact, some of those BB’s are not digital TV at all. Some are phone, PPV, internet, menus and On Demand type services. But why give all of the BB’s to every house? Switched Digital Video is the cable companies software that controls what BB’s you get in your cable.
Let us take a few minutes and talk about Switched Digital Video and why you should be aware of it.