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I am trying to recover some videos on a Video8 tape and was wondering how in general how analog video was written to tapes. I've been researching the NTSC specification and it seems like there are these vertical and horizontal sync signals. I am wondering if these signals are written to the Video8 tapes during record, or if only video frame data is recorded and the sync data generated upon playback by the playback device?

A little bit of old school electronics, but it would be helpful if any of you more experienced folks have any idea.

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This is just a short recall of what I remember.

The H sync tip, and chroma burst are stripped off and then restored with a standard sync tip after reading. Since the sync tip corresponds to past the the edge of the tape with some guard edge, there is a precision servo to sync the spinning head and tape speed to the standard rate derived from the Hsync standard rate. The chroma burst is inserted with the sync tip during playback.

There are two sets of gapped heads on the heliscan drum with gaps to correspond to the horizontal blanking interval (BHI)

Since the chroma burst is harmonically related to the H sync as well as V sync and tape speed, there are several servo PLL's to regulate tape speed and heliscan drum recording/playback head to synchronize all the signals back to the standards Hsync frequency.

The video signal itself is also converted from AM carrier to baseband to FM to tape and the reverse back to RF out on CH 2 or 3 or composite video out which is compatible with monitors on 75 Ohms.

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enter image description here enter image description here ref

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  • \$\begingroup\$ Sorry, still need some clarification. So on the tape, the video tracks only contain information about the video and not the vertical or horizontal sync pulses? In the second picture it's not clear to me where "playback video sync pulses" come from if not the tape itself. It's hard to find information on video8, the most useful resources have been in old books - if you can recommend any that would be great as well. Thanks. \$\endgroup\$ – Alex H Nov 16 '16 at 11:39
  • \$\begingroup\$ Correct Sync pulse and chroma burst is not stored on tape but track control pulses are included. The Capstan RPM and phase is sync'd to the recorded signal and visa versa when played back. So it is synthesized. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Nov 16 '16 at 14:11
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The luminance ("Y" or brightness) signal was FM modulated onto a high frequency carrier and written directly onto the tape. The chroma ("C" or color) signal was hetrodyned down to a sub-harmonic of the color subcarrier and combined with the luminance signal.

Because the tape speed is a couple orders of magnitude too slow to record such high frequencies, rotating heads were used to write long diagonal stripes on the tape, one for each frame of video. So it takes a playback machine with exactly the same dimensions and adjusted properly to read back the diagonal stripes of data. This is called "Helical-Scan" and is rather fiddly to get exactly the same mechanical alignment to allow perfect playback.

In some formats, the audio was written longitudinally along the edge of the tape, and in other formats, it was FM modulated onto a carrier and combined with the video onto the diagonal stripe.

Ref: https://en.wikipedia.org/wiki/8_mm_video_format#Video8

Ref: https://en.wikipedia.org/wiki/Helical_scan

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  • \$\begingroup\$ +1 for describing the separate chroma path. aka a "colour under" system. There was a third audio system, using the NICAM-728 digital encoding system, though that may have been restricted to PAL systems, so not applicable to NTSC. \$\endgroup\$ – Brian Drummond Nov 16 '16 at 11:08

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