Coax Cable Table
| Type | Impedance (ohms) | Core (mm) | OD (mm) | Shields | Typical use |
|---|---|---|---|---|---|
| RG-6/U | 75 | 1.024 | 6.86 | Double | Cable TV, satellite, video |
| RG-6/UQ | 75 | 1.024 | 7.57 | Quad | Quad-shield runs near interference |
| RG-8/U | 50 | 2.17 | 10.3 | Single | Amateur radio, Thicknet era |
| RG-8X | 50 | 1.47 | 6.1 | Single | Thin RG-8: mobile antennas, short HF |
| RG-11/U | 75 | 1.63 | 10.5 | Dual/quad | Long cable and satellite runs |
| RG-58/U | 50 | 0.81 | 5.0 | Single | Patch leads, thin Ethernet era |
| RG-59/U | 75 | 0.64 | 6.1 | Single | CCTV video, older TV runs |
| RG-62/U | 92 | โ | 6.1 | Single | ARCNET, automotive antennas |
| RG-174/U | 50 | 0.5 | 2.55 | Single | Wi-Fi pigtails, flexible jumps |
| RG-178/U | 50 | 0.31 | 1.8 | Single | PTFE, tight high-frequency runs |
| RG-213/U | 50 | 2.26 | 10.3 | Single | Radio power runs, EMC test |
| RG-316/U | 50 | 0.51 | 2.6 | Single | PTFE heat-resistant runs |
| LMR-400 | 50 | 2.74 | 10.29 | Double | Low-loss permanent runs |
Coax types sort into two electrical worlds, and the impedance column is the border: 50-ohm line (RG-8, RG-58, RG-174, RG-213, LMR-400) carries radio-frequency power - transmitters, Wi-Fi pigtails, amateur and commercial radio - while 75-ohm line (RG-6, RG-11, RG-59) carries signals that want low loss per dollar - cable TV, satellite, CCTV video. Impedance is geometry, not a label: it falls out of the ratio of the center conductor to the inside of the shield, so a 75-ohm cable is not a 50-ohm cable with different markings, it is built to different proportions.
The RG numbers themselves are a trap for the tidy-minded: RG stands for Radio Guide, a World War II-era military spec list, and the numbers are catalog sequence, not a performance ladder - neighbors RG-58 and RG-59 sit on opposite sides of the impedance border. What actually sorts the family is diameter, and the table makes the rule visible: fatter cable loses less signal per foot (RG-58 at 5 mm is a lossy jump rope next to LMR-400 at 10.3 mm), and the dielectric column adds the second axis - PE is the classic solid core, PF foam cuts loss further, and PTFE (RG-178, RG-316) buys heat resistance for wiring that runs past hot engine bays and amplifiers.
How to use
- Pick impedance first, by task: radio gear, transmitters and Wi-Fi hardware expect 50 ohms; TV, satellite and video gear expects 75 ohms. The connector threads may match, but the system behind them will not.
- Then pick diameter by run length: a short indoor jumper forgives almost anything, but every extra meter charges the loss column - long runs or weak signals step up from RG-58/RG-59 to the 10 mm class like RG-213, RG-11 or LMR-400.
- Check the environment last: a run past an engine bay, amplifier or heat duct calls for a PTFE dielectric type (RG-316, RG-178), and a bendy path to a small antenna calls for the flexible thin pair RG-174 or RG-178, accepting their higher loss.
Frequently asked questions
Can I swap RG-59 for RG-6, or the other way?
Yes when both ends are 75-ohm video or satellite gear: the impedance matches, F-connectors fit both, and the system does not care which jacket carries the signal. What changes is the budget: RG-6 has a fatter core (1.02 mm versus 0.64 mm) and denser shielding, so it loses less per foot and rejects interference better - which is why new satellite and cable TV installs specify RG-6, while RG-59 survives in older CCTV and short indoor runs where its higher loss is affordable. The swap trap is the other direction in spirit: RG-6 is stiffer and bulkier, so squeezing it into the same staple path as RG-59 takes more force, and a kinked RG-6 has lost its geometry - a dented cable is a spec change, not a cosmetic flaw. Quad-shield RG-6/UQ adds four shielding layers for runs that pass near power lines or other strong interference sources.
What happens if I mix 50-ohm and 75-ohm cable or gear?
The connectors will thread together, which is the trap - impedance mismatch never looks broken at the fitting. Electrically, the junction reflects part of the signal (measured as SWR or return loss): on a transmitter that wasted energy comes back as heat at the final stage and erratic power readings; on a receiver it shows up as ghosts and dipppy signal. Short, low-power hops tolerate the mismatch - a 75-ohm patch cord on a 50-ohm receive-only scanner often works for years - but the rule for anything long or anything transmitting is match the world: 50 to 50, 75 to 75, and use the correct connector family at the boundary rather than an adapter that quietly marries the two impedances.
Why is RG-58 lossy, and when is that fine?
Loss per foot scales roughly with frequency and inversely with how much metal the signal sees: RG-58 has a thin 0.81 mm core in a slim 5 mm jacket, so at radio frequencies it burns real signal - several dB over a 20-meter run, the kind of number that halves your transmit range. That is fine exactly where RG-58 lives: short patch leads, bench work, mobile whip feeds under three meters, and the classic thin-Ethernet era it grew up in. When the run grows or the power rises, the ladder in the table is the answer: RG-8X splits the difference at 6 mm, RG-213 at 10 mm handles power and long runs, and LMR-400 class foam-dielectric cable carries the lowest loss per dollar for permanent runs. Match cable class to run length, not to what is on sale.
Which coax do I use for a Wi-Fi antenna extension?
50 ohms, as short as the install allows - Wi-Fi sits at 2.4 and 5 GHz where every meter of even good cable eats double-digit percent of the signal, so the honest fix is usually moving the radio to the antenna (a USB or PoE outdoor unit) instead of extending cable. When a feedline is unavoidable: LMR-400 or RG-8 class cable for runs over a few meters, RG-58 for a short indoor hop, and the thin flexible RG-174 only inside equipment - at 2.4 GHz its per-meter loss is brutal. Keep connectors quality coax-series (RP-SMA and N-type for most gear), avoid adapter chains, and if the spec sheet lists loss per meter, add the two runs up before you mount anything: a cable plan that costs 6 dB has quietly erased half your radio.