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UHF/DirectTV combined through COAX?
In article ,
"Pat Beal" wrote: "Isaac Wingfield" wrote in message ... In article , (G.T.W.) wrote: On Mon, 20 Jan 2003 09:58:05 -0500, "Jim" wrote: 1 st what kind of tuner did you order? one for off air or Direct TV HD No such thing as HDTV or none HDTV dish, they point at sat that has it or not. sorry, but to get HDTV channels, it requires a slightly differant dish, one that has dual LNBs and is slightly wider. You have to pick up dual feeds in order to get the double-bandwidth HDTV provides. I don't think so.. One HDTV signal is about 16-18 MBits/sec. A single DirecTV QPSK stream can provide more than that (about 20 or about 27 MBits/sec. depending on which data rate they're using). I suspect the HDTV signals are coming from a different satellite (at a different location) from the cluster that provides the normal TV signals. The DirectTV system was designed *from the start* to be able to handle HDTV. Isaac D* HD channels are coming from the 110 and 119 orbital positions while most of the standard programming is from 101. A 3 LNB dish oval is needed for HD reception. They've been having a heck of a time getting 2 decent quality HD channels on one transponder. For a given receiver antenna (dish) size, there is a tradeoff between transmit power and bitrate. The way the birds are set up (at least the first-generation ones), there are 64 transmit tubes (TWTs), and they can be configured for 64 downlink "channels", or paralleled x2 for 32 with twice the power. Before the system went live, there was some uncertainty concerning how much power it would take to provide coverage to all of CONUS, so they wanted some flexibility. Also, the downlinks can be run at one of two bitrates (about 20 and about 27 MBits/sec. payload). Combined with the possible paralleling of TWTs, there are a number of ways they could set things up. 20 MBits/sec is more than enough for one HD signal, but nowhere near enough for two. 27 MBits/sec. could handle two, but with only 14 MBits/sec per video + audio, it's no wonder things are a little bit less than optimum. BTW, the audio takes up probably 256 KBits/sec, but certainly no more than 384 KBits. Isaac |
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