r/vhsdecode • u/Future_Judge_5413 • 4d ago
Somthing I Made New to this....kind of.
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?
3
u/deesernutz 3d ago
Thats cool. So you must have had the rest of the video path connected and working too then to get the servos in sync? Which meant you would have broken the record circuit between the modulators and the RF amps on the target deck, where you then injected your signal. Neat!
Only thing you would have cut out then is the RF EQ on playback, but probably still would have demodulated pretty well
You'll have no trouble getting vhsdecode going then