Quick Answer: A composite video RCA jack is a 75 ohm socket carrying one signal: luma, chroma and sync added together, about 1 V peak to peak into 75 ohm. The centre pin is signal and the shell is the return, connected to chassis earth at both ends in most equipment, which is exactly how 60 Hz hum enters. Usable bandwidth is roughly 5 MHz, enough for 480i or 576i and nothing above. Keep runs under 25 m (82 ft) on RG-59 and expect visible softness past 15 m.
The yellow socket is the cheapest video interface still in service, and nearly every fault reported against it is an earth problem rather than a bandwidth problem. A single 75 ohm coaxial cable carrying 1 V composite is robust. The return path shared with mains earth is not.
What the socket actually carries
Signal levels and bandwidth
Composite puts luma at 0,7 V and sync at 0,3 V below black, with chroma modulated on a 3,58 MHz subcarrier in the 480i system. Usable bandwidth is about 5 MHz. That is why text and thin lines smear: chroma and luma share one conductor with no way to separate them again.
Impedance and connector practice
The jack is 75 ohm, the cable must be 75 ohm and the source expects a 75 ohm load. A 50 ohm radio lead with RCA ends will work at 3 m and ring visibly at 30 m. The shell is the signal return, not a spare connection for a screen wire.
Earth loops and the 60 Hz bar
When the source and the display sit on different branch circuits, their chassis earths sit at slightly different potentials. Current flows down the screen at 60 Hz and the picture shows one or two slow horizontal bars. Lift the screen at one end, fit a video isolation transformer at the display, or move both units onto one circuit. Cutting the earth pin on a mains plug is not a repair.
Screening that avoids the loop
For a short unbalanced run, earth the screen at the display end only. Above 25 m put an isolation transformer at the receiving end, which breaks the loop while passing the 5 MHz band. Ferrite clamps cut radio pickup, not hum, and a thicker cable will not fix a potential difference.
Adapters, splitters and what they cost
Every passive part in the chain adds loss and reflection. A passive rca splitter divides the level by two and adds 3,5 to 6 dB of loss, so two displays from one source need a distribution amplifier rather than a Y lead.
| Path | Connector | Bandwidth | Ceiling |
|---|
| Composite | 1x RCA, yellow | 5 MHz | 480i / 576i |
| Component YPbPr | 3x RCA | 30 MHz | 1080i |
| S-Video | 4-pin mini DIN | 10 MHz | 480i, cleaner chroma |
| RF channel 3 or 4 | F connector | 4,2 MHz | 480i with interference |
| HDMI 2.0 | 19-pin | 18 Gbit/s | 4K at 60 Hz |
What the adapters can and cannot do
Adapters change connector geometry, not signal content. Feeding a component output into a composite input through rca to component video leads either gives a rolling monochrome image or nothing, because the display is looking for one signal with sync embedded and receives three. A tablet or phone source needs an active lightning to rca adapter with its own video encoder, and that adapter must be powered if the session runs past two hours.
Practical scenarios
- Situation: a gym feeds four displays from one player over 15 m (49 ft) runs. Use RG-6 rather than RG-59, drive each screen from a four-way distribution amplifier and keep the coax out of mains conduit.
- Situation: a boardroom projector shows hum only when a laptop charger is connected. Fit an isolation transformer at the projector input; the loop is the charger earth, not the video cable.
- Situation: a legacy camera feed must reach a monitor 40 m (131 ft) away. Composite will not hold 40 m on RG-59, so convert to HDMI at the camera end and run 18 Gbit/s cable instead.
- Situation: a wall plate feeds a TV through three couplers and shows a shadow right of every white edge. Replace the chain with one 12 m RG-6 assembly and the reflection disappears at the same time as the ghost.
FAQ
Does the yellow jack carry audio?
No. Composite video uses the yellow socket for picture only, while audio uses the white and red sockets. A video cable plugged into an audio socket gives a hum bar and no picture at all.
How far can composite video run?
About 25 m (82 ft) on RG-59 and 40 m (131 ft) on RG-6 before softness becomes obvious. Each coupler adds roughly 1 dB of loss and one reflection, so three joins on one run will show as a ghost.
Why is the picture black and white?
The chroma subcarrier is missing or the display is set to a monochrome input. Check that the cable is 75 ohm coax rather than a two-core audio lead, and confirm the source menu is set to composite.
