[mythtv-users] Crazy idea for cheap HDTV tuner card

[Cory Papenfuss]

 	OK folks.... here's a whopper.  I've recently gotten off on the tangent 
of using the "high-frequency" ADC on the bt87x chipset using the 'btaudio' 
linux driver.  It'll sample at rates of up to 448kHz, and can allegedly go 2x 
or maybe 4x that speed.  I have repeated the ideas in:
http://www.domenech.org/bt878a-adc/index-e.htm
http://www.domenech.org/bt878a-adc/index-decimator-e.htm

 	That led to another tangent of trying to use my now removed BT878 card 
from my mythv box as a general-purpose RF receiver/spectrum analyzer.  After 
taking a trip through gnuradio.org, it became apparent to me that's it might be 
possible to use software radio with a cheap bt8xx card as both an RF 
demodulator, and an A/D.  There are some slightly old threads (2002, 2003) on 
the gnuradio discussions boards to this effect.  Basically trying to pervert 
the VBI engine (in frame mode, not line mode) to spit out raw 8xFsc (28MHz 
NTSC, 35MHz PAL) data.

 	What does all this have to do with mythtv?  There has already been work 
on software demodulating HDTV streams using higher-end RF demod and A/D 
converters at 40MHz.  I've even ran across a benchmark on the order of 4:1 time 
on an "athlon" CPU (4 minutes of demod time for a 1 minute stream).
http://comsec.com/wiki?HowtoHdTv

 	If this works, it could allow HDTV reception from simple, bt8xx boards 
at the expense of enormous storage (approx 150 GB/hour?) and processing, of 
course.

 	Something to think about and perhaps develop interest in... if anyone 
else on this list is as twisted as I... :)  No wonder the gnu software radio 
folks have put an FPGA on their board.

-Cory

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