Video was coax’s first business, and it is still the medium where video distance problems get solved. A CCTV camera’s composite signal, a studio’s SDI feed and a legacy projector’s component input all ride the same 75 ohm pipe – at very different rates and over very different distances. This article maps the three video formats that still use coax, the distance each one survives, and the point where the honest answer becomes twisted pair or fiber.

Coaxial Video Cables: What Rides Coax, and How Far It Gets

Video Over Coax: The Three Classics

Composite video (CVBS) is the original: one 75 ohm coax carries the entire picture – luminance and chrominance summed onto one carrier. It is the native format of CCTV, of VCR-era consumer gear, and of a huge installed base of security cameras. One cable, one BNC or RCA, a picture that is perfectly adequate at standard definition and nowhere near enough for 4K.

SDI (Serial Digital Interface) is the pro revival of the same idea: digital video serialized onto 75 ohm coax, at 1.5 Gbps for HD, 3 Gbps for 4K at 30 frames, and 6 and 12 Gbps for 4K and 8K at full frame rates. SDI kept coax’s virtues – simple cabling, long unpowered runs, no protocol negotiation – and dropped composite’s ceiling. It is why broadcast, sports and large-venue video still specify 75 ohm BNC patch bays.

Component video splits the picture across three 75 ohm coax lines (plus audio on separate pairs), which removes the composite summing limit and carried 1080p before HDMI made it obsolete. It survives in installed projectors and players, and its cables are the three-coax bundles or matching sets you still see in AV racks.

Composite (CVBS) and Its Limits

Composite’s limit is bandwidth, not cable. The format itself tops out near standard definition – roughly 4-6 MHz of video bandwidth – so even perfect coax cannot make it 1080p. What the cable decides is how far that modest signal survives: over RG59 or RG6, a clean composite run is comfortable to about 150-200 metres, with the image softening as loss eats the high frequencies first – edges go soft before the picture fails outright.

The format that started it all

That failure pattern is the field tell for a composite problem: a camera that is sharp up close and smeared at distance, or clean at 8 am and soft after a hot afternoon (loss climbs with frequency and, slightly, with temperature). The fixes are in order: better cable gauge, fewer joints, a distribution amplifier at the midpoint, or moving the segment to a digital format.

SDI Over Coax: The Format That Kept the Medium

SDI changed what coax carries but not where it carries it: 75 ohm, BNC-terminated, unpowered, and distance-limited by loss exactly like everything else on the medium. The standard cable run for 1.5 G HD-SDI is 100 metres on RG6; 3 G and 6 G versions shorten the comfortable distance because the same loss budget now guards a faster eye pattern, and 12 G pushes toward the 50-metre class on standard cable.

The discipline SDI adds is impedance purity: the run must stay 75 ohm from camera to receiver, with matched BNC joints, or the digital eye closes and the picture fails catastrophically – no soft gradient, just no sync. That is the difference between the composite world (degrades gracefully) and the SDI world (works perfectly until it does not). Designers treat an SDI run like a data line: measured, terminated, and documented.

Where a venue outgrows the distance, the industry’s answer is not a fatter coax but a different medium – fiber for the long hall, or the HD-over-CAT6 balun pairs that moved the signal onto the building’s network cabling. Coax remains the patch-bay standard because for under 100 metres it is the simplest correct answer.

Distance, Loss and the Practical Ceiling

Every video-over-coax design is the same arithmetic: the format’s bandwidth, the cable’s loss at that bandwidth, the joints in the chain, and the receiver’s tolerance. Composite forgives the most, 1080p component sits in the middle, and SDI at the top data rates forgives the least. The cable choices that buy distance are the same across all three: larger gauge, fewer joints, and an amplifier or distribution amp placed where the budget says, not where the symptom appears.

The honest ceiling is format-set, not cable-set. No coax will carry 8K composite; no amount of shielding fixes a mismatched SDI joint. Coaxial video cable is the right medium while the signal stays within its physics – and the moment it does not, the answer is a different medium, not a better cable.

Choosing the Cable for the Video Job

CCTV and legacy AV: 75 ohm RG6 (or RG59 on short legacy runs) with BNC at the pro end and RCA at the consumer end, crimped or soldered, and counted in metres against the 150-metre comfort line. SDI installs: 75 ohm RG6 or the specified low-loss variant, BNC throughout, every joint matched, and the run measured before it is documented as done. Component retrofits: a matched three-coax set in 75 ohm, the three lines the same length to the centimetre, because a mismatched pair shows up as colour shift.

In all three, the connector is as specified as the cable: BNC for anything pro, RCA for anything consumer, and the ohm value printed on both. A video cable is a system – medium, joints and termination – and the weakest of the three is what the picture actually sees.

Video Formats Over Coax, Compared

Real-World Application Scenarios

The security shop is composite’s home: cameras on 75 ohm RG6 drops to the NVR, BNC at both ends, distribution amplifiers where a run forks, and the 150-metre number on every design sheet. The studio and venue world runs SDI: a patch bay of BNC couplings, 100-metre camera feeds to the switcher, and fiber taking over the moment a feed crosses the hall. The consumer-retrofit world lives with component: a matched three-coax set from a 2008 player to a projector that predates HDMI, the lines cut to identical lengths so the colour stays put. Three trades, one medium, and the same rule underneath – the cable serves the format, and the format sets the ceiling.

Related reading: coax versus Cat6 for CCTV; SDI video over coax; composite video into BNC coax; BNC coaxial cable assemblies; how coax loss climbs with frequency; RG6 coax cable guide.

Recommended Internal Resources

Editorial Note: Internal linking recommendation: route the CCTV and studio readers from this article: link the coax-versus-Cat6 CCTV comparison, the SDI-over-coax piece, the composite-to-BNC cable guide and the BNC coax assemblies, with the attenuation article as the shared physics reference.

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