CABL Forum - Re: Digital modulators

This will not be a short answer, but I'll try.

The two channels you mentioned (FOOD and HGTV). If they are analog channels, you'll still need two receivers. Each channel will then go through a A to D converter such as an SE2000 and converted to digital.

Any digital channels in the same "stream" - your example of five channels, but only using two- can be added to the system and passed through "as is", or they can be cherry picked using a statistical multiplexer like a Moto TMX2010.

For analog channels converted to digital, you assign a max data rate per channel in the TMX, say 3.8 MBPS. The TMX uses a card to control the SE2000, and will only allow the channel a max data rate of 3.8 MBPS.

Digital channels, either analog that have been converted, or channels received as digital, are packaged into Multiple Program Transport Streams by the TMX and assigned to an MPTS UDP multicast address. Each multicast address becomes a stream assigned to a six MHz digital QAM carrier provided by the SEM. The SEM can output up to eight QAMs. The SEM itself is a 1RU "pizza box".

The max data rate for a QAM at the SEM is 38.8 MBPS. Assigning 3.8 MBPS to each channel allows for a maximum of 10 channels (3.8 x 10 = 38 MBPS) for each QAM. Some channels, say ESPN, require higher bandwidth to generate the picture and can be set to 5 MBPS (5 x 7 = 35 MBPS), providing a max of 7 channels to the QAM. HDTV channels require 19 (+/-) MBPS (19 x 2 =38 MBPS), so only two HDTV channels can be sent out over a single QAM.

I can tell that this is getting a bit long for a post, but I hope it helps.

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Re: Digital modulators