Just so where are all on the same page ( and I could go into far greater detail but i don't want to bore you )
QAM-Quadrature amplitude modulation
is a modulation scheme which conveys data by changing (modulating) the amplitude of two carrier waves. These two waves, usually sinusoids, are out of phase with each other by 90° and are thus called quadrature carriershence the name of the scheme.
Unlike the analog Sinusoid or " sine wave which curves up and down much like alternating current does. And in case you wanted to know- " The television signal is made up of two parts, both related to each other by the frequency of the carrier signal. The image signal is amplitude modulated and occupies about three fourth of the total bandwidth (which is usually 6 megahertz) the audio component of the TV signal is frequency modulated and has a frequency in the range of the upper quarter of the band frequency range. "
In QAM, the constellation points are usually arranged in a square grid with equal vertical and horizontal spacing, although other configurations are possible. However it appears that in America we have chosen the " square gird " In the same space that one could place a 6 Megahertz analog signal, we can now place 12 digital channels in a 256 QAM pattern. This makes digital signal very desirable.
Unlike analog signal that can bleed over into an adjacent channel, and cause " co-channeling " Digital will NOT bleed over at all. The reason should be quite clear. With analog the Sinusoid can be distorted more easily ( on your analog radio you know doubt have heard another station bleed through ) when this happens it is possible to get the audio or picture of another tv station over yours. With digital we are not relying on these waves to stay so harmonious. We are relying on a grid to stay square, when it does not there is nothing left to bleed. You will also find many adjacent channels are gone as well. To keep our signal pure we simply need to keep the system " air tight " If the system is not air tight then we have what is know as BER ( binary digit error ) When to many errors occur you will experience " jittery audio " and or" tiling " or macro blocking " Most common cause of a system that is not air tight are bad connectors, poorly shielded cable, or low signal. Oh and don't forget when the customer decides he is qualified to do his own wiring, this is a major cause of the problems we find.. Every time I go past Radio Shack I cures those worthless gold plated screw on fittings and that RG59 cable!
Ok back to what I was saying....With analog signal the sound becomes weaker and weaker, the picture becomes grainy or snowy. With digital signal when you have BER it just plain disappears! There is NO bleed over, well at least in my 10+ years as a system-network tech for cable tv. Of course running a 256 QAM is more risky than a 64 QAM signal. But Cable television has got it perfected " as long as it is a air tight system " Anyone with a digital box will have to admit that a digital picture is clearer and more defined than without the box. I expect someday radio will also achieve this.
Sedond,
Your quote
" and, no, conventional fm isn't going anywhere any time soon "
Since you have said it I can take it as gospel? I am wondering if your the president of the FCC?
QAM-Quadrature amplitude modulation
is a modulation scheme which conveys data by changing (modulating) the amplitude of two carrier waves. These two waves, usually sinusoids, are out of phase with each other by 90° and are thus called quadrature carriershence the name of the scheme.
Unlike the analog Sinusoid or " sine wave which curves up and down much like alternating current does. And in case you wanted to know- " The television signal is made up of two parts, both related to each other by the frequency of the carrier signal. The image signal is amplitude modulated and occupies about three fourth of the total bandwidth (which is usually 6 megahertz) the audio component of the TV signal is frequency modulated and has a frequency in the range of the upper quarter of the band frequency range. "
In QAM, the constellation points are usually arranged in a square grid with equal vertical and horizontal spacing, although other configurations are possible. However it appears that in America we have chosen the " square gird " In the same space that one could place a 6 Megahertz analog signal, we can now place 12 digital channels in a 256 QAM pattern. This makes digital signal very desirable.
Unlike analog signal that can bleed over into an adjacent channel, and cause " co-channeling " Digital will NOT bleed over at all. The reason should be quite clear. With analog the Sinusoid can be distorted more easily ( on your analog radio you know doubt have heard another station bleed through ) when this happens it is possible to get the audio or picture of another tv station over yours. With digital we are not relying on these waves to stay so harmonious. We are relying on a grid to stay square, when it does not there is nothing left to bleed. You will also find many adjacent channels are gone as well. To keep our signal pure we simply need to keep the system " air tight " If the system is not air tight then we have what is know as BER ( binary digit error ) When to many errors occur you will experience " jittery audio " and or" tiling " or macro blocking " Most common cause of a system that is not air tight are bad connectors, poorly shielded cable, or low signal. Oh and don't forget when the customer decides he is qualified to do his own wiring, this is a major cause of the problems we find.. Every time I go past Radio Shack I cures those worthless gold plated screw on fittings and that RG59 cable!
Ok back to what I was saying....With analog signal the sound becomes weaker and weaker, the picture becomes grainy or snowy. With digital signal when you have BER it just plain disappears! There is NO bleed over, well at least in my 10+ years as a system-network tech for cable tv. Of course running a 256 QAM is more risky than a 64 QAM signal. But Cable television has got it perfected " as long as it is a air tight system " Anyone with a digital box will have to admit that a digital picture is clearer and more defined than without the box. I expect someday radio will also achieve this.
Sedond,
Your quote
" and, no, conventional fm isn't going anywhere any time soon "
Since you have said it I can take it as gospel? I am wondering if your the president of the FCC?