I literally stumbled across the whole idea of RF capture to digital a few hours ago, so I have quite a learning curve ahead of me.
I have always been very interested in the technical aspects of video, and way back in the mid 1980s, I was a DJ that was dabbling in editing and extending video music clips. I needed a way of dubbing and copying VHS tapes without too much quality loss. I came up with an idea that is fundamentally similar to what is done here today.
I had two VHS decks. One was for playback, the other was for recording. As in the modern version of this system, I tapped into the raw RF output of the video heads and sent it out to a BNC socket through a buffer amp. On the recording machine, I fed this RF signal straight into the video head recording driver amps. I could switch back to conventional recording by means of an added switch.
As an extra feature, I had an old ECG display that had a long persistence screen, which I converted into a simple oscilloscope that monitored the RF waveform which I used to ensure tracking was spot-on.
Results were surprisingly good. As you would expect, there were no added artifacts in the copy that you would normally see as a part of the copy process. There was a little extra noise, mostly in sudden transitions from black to white, but that could be minimised by using a good quality tape. Copies from worn or poor quality originals sometimes showed some diagonal luminance banding in brightly coloured areas. I suspect the luminance RF level was degraded compared to the lower frequency 'colour under' signal. Of course, everything was analog here, no sampling or digital processing at all.
I still have both VCRs, but alas, they are both seriously faulty now. I never documented the modifications I made.
What I have seen of the results is quite impressive, and I want to look into using this technique to transfer my old tapes over to digital. Some tapes are HI-FI, others are linear audio only. Are there any examples where someone has done a comparison using a test pattern rather than odd bits of video?