7.4 Video on 75 Ω coaxial jacks (VID-75)

VID-75 is the 75 Ω coaxial interface of EIS: video between products on 75 Ω coaxial cable with RCA, BNC, or SMA jacks. It carries the video reference of a row, black burst or bi-level or tri-level video sync of a 7.3 format, behind the panel from one source to every module that locks to it: this distribution is what conforms to EIS for interoperability, and a module claims it port by port with the features VID-REF-IN, VID-REF-OUT, VID-REF-PASSTHRU, and VID-REF-LOOPTHRU below. A feature describes what happens behind the panel or inside the case, so VID-75 is the interface those features use and is not claimed on its own. A picture on a coaxial jack on the front, composite or component video, is an external interface like line-level audio: it is listed in the port list with its Annex I class (VID-CVBS, VID-YPBPR, VID-RGBS) and the formats it carries, claims nothing, and EIS recommends that it take the COAX-IN or COAX-OUT form of this clause. A product with VID-REF-PASSTHRU ports beside its VID-REF-IN, usually a bus board, is a video reference distributor that fans the reference out to several modules, and a cable of the interface joins them. The tables are in data/video_75.json.

The front of a module is patched (7.2): the reference never reaches a patch jack (SIG-015), and a module that generates or locks to an external video reference takes or gives it at a video reference port on its rear (V75-010).

Video reference ports and claims

A module names what each of its video reference ports does, and claims it, with one feature per port kind. The difference between an input and an output is the one a buyer needs most: a VID-REF-OUT can be the row's reference, a VID-REF-IN follows it, and a pass-through is neither a source nor a second input.

A module that claims VID-REF-IN shall lock its video timing to the video reference at its VID-REF-IN port, a COAX-IN on its rear, and list the formats it locks to (V75-011). A module that claims VID-REF-OUT shall give a video reference of a listed format at its VID-REF-OUT port, a COAX-OUT on its rear, that it generates itself (V75-012); a copy of a reference it takes at VID-REF-IN is a VID-REF-PASSTHRU, not a VID-REF-OUT. A module shall claim VID-REF-PASSTHRU only with VID-REF-IN (V75-013); its VID-REF-PASSTHRU port shall be a COAX-PASSTHRU, a buffered copy of the reference at VID-REF-IN driven as a COAX-OUT into one COAX-IN load, and be marked PASSTHRU (V75-013). A module shall claim VID-REF-LOOPTHRU only with VID-REF-IN (V75-014); its VID-REF-IN shall then be a COAX-LOOPTHRU, two bridged jacks on one line with a termination switch that presents 75 Ω to 0 V across the line when on and no load when off, marked TERM, and the module shall lock the same with the switch on or off (V75-014).

The claim line names every port kind the module has: module (VID-REF-IN), module (VID-REF-IN, VID-REF-PASSTHRU), module (VID-REF-IN, VID-REF-LOOPTHRU), module (VID-REF-OUT), or module (VID-REF-IN, VID-REF-OUT) for a generator that also genlocks; its picture jacks are in its port list and add nothing to the line. Claiming any VID-REF feature brings the jack and port rules of this clause with it. A distributor claims VID-REF-IN and VID-REF-PASSTHRU, bus board (PWR-BUS-OUT, VID-REF-IN, VID-REF-PASSTHRU) (6.5); distribution is a capability of whatever product has those ports, not a product type.

Jacks

Every jack in a VID-75 tree shall be an RCA, BNC, or SMA jack (V75-001); EIS recommends that it be insulated from the panel (7.1). Its center pin shall carry the video signal and its shell shall be 0 V (V75-002). The three jack types are electrically the same here: an SMA jack is a 50 Ω connector, a catalog BNC jack is as often 50 Ω as 75 Ω, and an RCA jack has no controlled impedance, but each is electrically short at video frequencies, below 100 MHz, so the discontinuity does not matter and either BNC impedance serves. A product picks the one that suits its panel, and a cable may change type from one end to the other; a cable with an SMA end is a 50 Ω assembly for that end, and the same argument covers it. A video reference port shall be marked beside it as an input (IN), an output (OUT), a pass-through (PASSTHRU), or, for a loop-through pair, with its termination switch (TERM) (V75-016); V75-008, which asked the same of every coaxial port, is removed and its number stays unused.

Topology

A tree is the star of cables from one source to the VID-REF-IN of every module in it: the source is a VID-REF-OUT, or an external reference arriving at the VID-REF-IN of a distributor, and the branches are its VID-REF-PASSTHRU ports. The VID-REF-IN is the tree's designated input, named in the port list (V75-011), and terminated as every COAX-IN is (V75-015).

A VID-REF-OUT or VID-REF-PASSTHRU port shall drive one COAX-IN load, and an output shall not be split passively to several terminated ports (V75-005): a second termination on the same output drops the level to two thirds, and a third to half. A COAX-OUT or COAX-PASSTHRU port shall pass the video reference with a −3 dB bandwidth of at least 30 MHz into a 75 Ω load (V75-017): a tri-level video sync edge is 54 ns ± 20 ns (SMPTE ST 240), and 30 MHz keeps it inside that tolerance through a chain of pass-throughs.

Video reference ports

Every video reference port shall be a COAX-IN (75 Ω to 0 V at the jack), a COAX-OUT (75 Ω series source driven at twice the line level), a COAX-PASSTHRU, or a COAX-LOOPTHRU port, never a patch jack (V75-015); the four port modes are defined in the summary, and a product with one claims the matching feature; the identifiers V75-003, V75-004, V75-006, and V75-009 are unused, and the register records what each was. The termination and the series source are 75 Ω within ±5 %; a loop-through pair with TERM off bridges the line at 10 kΩ or more in parallel with 20 pF or less. A picture port, composite or component video on an RCA, BNC, or SMA jack on the front, or a digital port such as SDI on a BNC jack, is named by its Annex I class in the port list; EIS recommends the COAX-IN termination and the COAX-OUT back-termination of this clause for an analog picture port, so that it drives and loads a 75 Ω line the same way the reference does.

A module that generates or locks to an external video reference shall take or give it at a video reference port on its rear (V75-010): the reference is system cabling, wired once behind the panel, and the patch field carries patched signals only (SIG-015, 7.1).

The patch jacks of a video module use MOD-VIDEO (7.2). The video reference waveform follows the selected 7.3 format: black burst for the two interlaced formats, bi-level video sync for any standard-definition format, tri-level video sync for any high-definition format. Line level, in this clause, is the level of the signal's own standard at a terminated input: the 1 V p-p composite scale for black burst (pulse tip −300 mV, white +700 mV), 300 mV p-p for bi-level video sync alone (pulse tip −300 mV, blanking 0 V), and ±300 mV about blanking for tri-level video sync (SMPTE ST 240 and ST 296). A buffered distributor may AC-couple its PASSTHRU outputs when its manual says so.

Cables

A VID-75 cable shall be a 75 Ω coaxial cable, with RCA, BNC, or SMA plugs, that connects center pin to center pin and shell to shell at both ends (V75-007).

Summary