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Discussion Starter · #1 ·
Would it be possible to take the output of two separate Dish Network 5000 HDTV modulators -- one configured for channel 3, one set for channel 4 -- and combine the signals, feed into a single decoder (such as a Panasonic 50 or 51) antenna input, and then simply tune the box to either channel to get each satellite signal?


Would a special "wideband" combiner/splitter be required to do this, or would a standard inexpensive CATV combiner/splitter work?


If it's the former, who makes something like this?


Thanks,


Steve
 

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Well, I'm using a TruSpec SC3 to combine channel 3 out from my 2700 with my OTA, with no problems on any channel. I know somebody has combined 2 satellite IRD's with one of these with no interfernce (1 set on 3, the other on 4) (granted, this was 2 NTSC sources). See the following thread for info.
http://www.dbsforums.com/ubb/Forum2/HTML/002752.html


[This message has been edited by Scooper (edited 05-26-2001).]
 

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I don't claim to understand this very well; perhaps someone will clarify:


8VSB is generated by first creating a double sideband RF signal. That signal takes up ~10 MHz, double that of a single sideband, and more than the 6 MHz allocation of an ATSC channel. The sidebands are redundant; each is a mirror of the other. In 8VSB the lower sideband is removed almost completely, leaving only the upper sideband, about 5 MHz wide. That fits within the 6 MHz channel.


The 5000 modulator uses the Zenith 8VSB modulator. This chip is inexpensive and intended for consumer applications. As such, it doesn't chop off the lower sideband. The receiver doesn't care; it will only look at the upper sideband. But that means that the lower sideband will overlap the channel below it.


So you can't combine channel 3 and 4 because the lower sideband of channel 4 would overlap channel 3. The only way to do it would be to remove the lower sideband of channel 4, and that would require a fairly precise, and probably expensive, filter.


Another possible way of doing it would be to shift one of the channels to something other than 3 or 4. Again, that would probably require expensive equipment.


The cheapest way to do it would be to use a coax switch, or to just change the channel with your 5000 remote!

 

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I use a Winegard signal combiner that blends my modulator's channel 3 output with an antenna feed that contains adjacent NTSC channels 2 and 4 as well as digital 9, 14, 18, 19, 32, 35, and 41. My TU-DST51 tunes all digital channels including the modulator's 3, but I haven't tried NTSC reception from the combiner's output to see if the modulator introduces any interference.

Charles
 

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For about six months I used a TruSpec combiner to combine the Ch. 3 output of the Dish 5000's HD modulator with the output of an OTA antenna. The combiner output fed a TU-DST51/PV-HD1000 recording combo.


I had persistent problems with digital breakup. I recorded dozens of movies from HBO-HD and Showtime-HD and many of those recordings exhibit digital tiling or brief audio dropouts every few minutes.


In trying to troubleshoot this I replaced just about every piece of equipment in this chain, including installing a 32-inch dish pointing at Echostar 3.


The problem did not clear up until I removed the combiner from the signal path and went back to using an A/B switch at the 50's input. Since I did this, I have had very little problem with digital breakup.


There is a strong local NTSC signal on OTA channel 4, and I suspect that this was my problem.


Very likely, more expensive broadcast-quality filters and combiners would do a better job. Rather than complicate things further I've decided to live with the inconvenience and occasional botched recordings that result from having to use the A/B switch.


------------------


Ron Gomes
 

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The only success I had with feeding two 5000/mods through a signal combiner is the use of an earlier dealer version of 5000/mod which output at chs 14/15 and the consumer version at chs 3/4. The dealer version of 5000/mod is as rare as a BEV 5000/mod and can no longer be found. To make the story short, A/B switch may be the only way, of course you must remember to switch for timed recording.


Anyone who has more than one working 5000/mods should consider himself real lucky at this time http://www.avsforum.com/ubb/smile.gif


[This message has been edited by jacmyoung (edited 05-26-2001).]
 
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