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

[Roger Heflin]

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.

                               Roger