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Posted: 02 Apr 2020, 02:58 

I know this isn't strictly LaserDisc related, but Oyvindln from Norway has made some great progress on VHS decoding. He forked the ld-decode git and heterodynes VHS's chroma signal up to 3.58MHz/4.43MHz. He recently implemented NTSC support and Simon's ld-analyse tool handles it well. Currently there is a need to blend the luma and chroma images in post-processing as there are two tbc files, but he is working on a script to combine them. Thanks to him, others for submitting RF samples, and the ld-decode project as a starting point, here's what we have so far!

https://i.imgur.com/zz8EI5l.png
https://i.imgur.com/0MXZJFN.png
https://i.imgur.com/ZDFN6So.png
https://i.imgur.com/xAIgAIL.png
https://i.imgur.com/8t6LQgW.png
https://i.imgur.com/si0PabD.png
https://i.imgur.com/xSCZagH.png

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Posted: 22 Dec 2020, 03:55 

Here's a pretty nice software defined QAM video decoding example, luma only.

https://www.youtube.com/watch?v=yvfZE28I75Y

Dirty FM video decoding has been done unofficially with the symbol decoder:

https://www.youtube.com/watch?v=rl8ACNnjPFA

Still waiting on my amplifier.

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Posted: 06 Apr 2021, 00:42 

Using the correct card, with player grounded to PC, termination, and gain brought down to 25 to avoid clipping, I'm getting black SNR of about 36dB and a good result. There's some constant noise in the red background of the program index screen, but this may just be the disc. The text is sharp and noise free. Still some 60Hz wavy pattern that is stationary in the image, likely due to mains hum in this room. I'll be moving my workflow at some point to try and isolate that.

https://i.imgur.com/K2szx9p.png

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Posted: 06 Jun 2022, 20:42 

Here's a good analogy for impedence matching. If you're ever driving down the highway and roll down your driver side window, the air may oscillate inside the cabin. There is negative pressure drawing air in following by positive pressure pushing it out. This is a reflection of air pressure. But you if you roll down your passenger window the same amount, the oscillation stops.

The wind is the RF signal, and your driver and passenger side windows are the input and output impedence. If the resistance on both ends doesn't match, you will get oscillations (ringing) and reflections, and non-ideal voltage/pressure on the output end.
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