The way this works is that the local broadcaster is transmitting a 6MHz 8-VSB modulated RF carrier. This modulation method/spectrum allotment allows for up to 19.39 Mbps for digital video bandwidth. A single HD service can be anywhere from 9 Mbps to 19 Mbps, depending on the type of content, and the desired amount of services the broadcaster wants to send over the 19.39 Mbps transport. The same is true for SD services, only these can vary from 3 Mbps to 6 Mbps typically. So they can send 1 HD & 1 SD, 1 HD & 3 SD, 4 SD, or any other configuration they choose.
Then there is the modulation scheme you, the Cable MSO send to your customer. I presume (based on what you said) that you are using 256 QAM, which can output 38.81 Mbps in a 6MHz RF carrier(for video purposes).
So you are taking 2 of those 19.39 Mbps 8-VSB transports & placing all of their subcomponents onto your single 256 QAM carrier(38.81 Mbps).
Hope that helps a little.
Re: Digital and Sub Channels, HD and SD
Member #: 46734
Registered: 6/11/2006
Posted:
54
Name:
Steve
Occupation:
Engineering Manager
Location:
USA
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