16-09-2021, 12:22 PM
(This post was last modified: 16-09-2021, 12:31 PM by ppppenguin.)
I very much doubt that direct colour on any helical scan VTR will give sufficient subcarrier stability to lock a crystal oscillator. There is a whole spectrum of jittter due to mechanical irregularities. Varies with basic mechanical design, machine alignment, servo quality, tape wear and heaven knows what else.
All non-broadcast VTRs (VHS, Betamax, V2000, U-Matic etc) used colour under to record composite video. This was mainly because of limited bandwidth, but it also simplified the process of recovering a stable colour subcarrier during replay.
By contrast, all broadcast VTRs that recorded composite signals did so directly**. The main ones were Quadruplex, B format, C format and IVC 9000. All used highly sophisticated timebase correctors to recover a stable signal that could be locked to an external video reference. Before digital video processing these TBCs were frighteningly complex. For example part of some TBC designs used variable LC delay lines to give the finest vernier correction. The capacitors of a convenional delay line were replaced by varicap diodes. The terminations had to be varied in sympathy with the delay to minimise reflections due to mismatch.
Later broadcast VTRs such as Betacam, BetaSP and M format had component YCbCr signal paths throughout. This solved a lot of problems. Then the world went digital.
To come right back to the start of this thread, where are we likely to find 405 line tapes today? Obviously we can make our own, as Peter has done. Many earlier non-broadcast VTRs would handle 405 as easily as 625, apart from any dropout corrector problems. The only intentional 405 formats were the Sony CV2000 with its horrible skip field recording process and the multistandard Quadruplex machines such as the Ampex VR2000. A very few people in world have working Quad machines. Fewer still have ones that are multistandard (405/525/625/819) and in working order. One such person, possibly the only one in the UK, is BECG chairman Paul Marshall.
**The digital D3 VTRs recorded composite signals. They were often used as a digital "drop-in" replacement for C-format.
All non-broadcast VTRs (VHS, Betamax, V2000, U-Matic etc) used colour under to record composite video. This was mainly because of limited bandwidth, but it also simplified the process of recovering a stable colour subcarrier during replay.
By contrast, all broadcast VTRs that recorded composite signals did so directly**. The main ones were Quadruplex, B format, C format and IVC 9000. All used highly sophisticated timebase correctors to recover a stable signal that could be locked to an external video reference. Before digital video processing these TBCs were frighteningly complex. For example part of some TBC designs used variable LC delay lines to give the finest vernier correction. The capacitors of a convenional delay line were replaced by varicap diodes. The terminations had to be varied in sympathy with the delay to minimise reflections due to mismatch.
Later broadcast VTRs such as Betacam, BetaSP and M format had component YCbCr signal paths throughout. This solved a lot of problems. Then the world went digital.
To come right back to the start of this thread, where are we likely to find 405 line tapes today? Obviously we can make our own, as Peter has done. Many earlier non-broadcast VTRs would handle 405 as easily as 625, apart from any dropout corrector problems. The only intentional 405 formats were the Sony CV2000 with its horrible skip field recording process and the multistandard Quadruplex machines such as the Ampex VR2000. A very few people in world have working Quad machines. Fewer still have ones that are multistandard (405/525/625/819) and in working order. One such person, possibly the only one in the UK, is BECG chairman Paul Marshall.
**The digital D3 VTRs recorded composite signals. They were often used as a digital "drop-in" replacement for C-format.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
