Annex F (informative) — Video sync distribution

How to bring one video sync to every video module in a system. The video sync travels behind the panel on the 75 Ω coaxial interface of 8.2, from a COAX-OUT to each module's COAX-IN. It never travels on a patch cable: a patch jack carries patched signals only (SIG-015), and a module takes or gives the video sync at a rear port that its claim file lists by mode (SIG-018).

The video sync is black burst, or bi-level or tri-level video sync. Pictures travel between products on the same 75 Ω cabling, but the two are not interchangeable at a COAX-IN.

EIS · Video sync in a row: direct links, a THRU chain, or a star A link, then a chain of COAX-THRU generator COAX-OUT module COAX-IN · THRU module COAX-IN · THRU module COAX-IN · THRU one COAX-OUT; each buffered THRU drives the next COAX-IN never a patch jack (SIG-015); a THRU is not an output (V75-007) VID-75 star generator COAX-OUT bus board COAX-IN, buffered THRU × n module COAX-IN module COAX-IN module COAX-IN one COAX-IN per THRU (V75-003) one source per tree (ASM-007) Video sync is rear coaxial cabling, wired once. A direct link suits a few modules; a chain of buffered THRUs, or one looped run, suits a row whose modules have them; a star suits many modules on one video sync. A facility video sync enters at a BNC on the enclosure's wall; no BNC is inside the case (SIG-017). Jack types may be mixed in a tree; an output is never split passively.

Situation Typical choice
A few modules, and a generator with several COAX-OUT ports A direct coaxial link from a COAX-OUT to each module's COAX-IN; no distributor
A row of modules with buffered COAX-THRU A chain: the generator's COAX-OUT to the first COAX-IN, that module's COAX-THRU to the next COAX-IN, and so on; each buffered THRU drives one input
Modules with looped COAX-THRU One cable run through each module's COAX-IN and looped THRU, with TERM on at the last module only
Many modules locked to one video sync A star: a distributor, usually a bus board that carries the tree (BUS-020), with one COAX-THRU for each COAX-IN
A facility that distributes black burst or tri-level video sync between racks The facility video sync at a BNC on the enclosure's wall, wired inside to the distributor's COAX-IN on RCA or SMA (SIG-017)
Two rows, one for performance and one for processing A distributor in each row, or one coaxial link from the first row's tree to the second row's COAX-IN

A tree may mix jack types. Each output drives one terminated input (V75-003); see 8.2. A COAX-THRU is not a source: a tree needs one COAX-OUT, or an external video sync at a designated COAX-IN (ASM-007), and the claim files say which port is which.

A module's front patch jacks carry its pictures, ramps, keys, and control (7.3). None of them is the video sync, so a patch never changes a module's timing.

Many video modules in use take their video sync on a rear 2 × 7 ribbon header, which is not a port of 8.2. Such a header mates a power ribbon socket, so BUS-011 applies to it (6.4), and the port list gives it as unclassified, named for what it connects to (Annex G). Such a module does not meet SIG-018 unless it also takes the video sync at a COAX-IN on its rear.