[mythtv-users] OT: ATSC/QAM Encode to distribute HD over longer runs.

Roger Heflin rogerheflin at gmail.com
Sat May 10 01:45:35 UTC 2008

Chris Ribe wrote:

>> But as to your second point -- an ATSC channel is the same 6 MHz
>> as an NTSC channel; once you've produced it, probably at a
>> standard 'channel 3' setting, can't you use a $50 modulator
>> (http://www.smarthome.com/7764.html is the first to hand) to
>> assign it to a dead channel that you create with a notch filter? Add
>> another frontend, add another modulator. You should be able to
>> handle four or five channels that way.
> No, that won't work.  The modulation schemes are substantially
> incompatible.  A 6Mhz NTSC band contains separate signals for luma, chroma,
> and audio.  If you fed an RF modulator like the one you linked with a
> SMPTE-310 (baseband ATSC, roughly speaking) signal on the video input, it
> would output an undecodable mangled signal.
> This isn't to say that an ATSC compatible RF modulator need be any more
> expensive than an NTSC model, just that currently available NTSC models
> wouldn't work.

I would think at min you would need something to take a proper ATSC bitstream 
and use the 8VSB or the cable modulation scheme to modulate it onto a channel, 
and I would not think that putting that on something like USB would take cost 
that much to make, so long as the computer was providing the proper bitstream to 
start with.


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