What Coaxial Cable Is
Coaxial cable carries RF (radio frequency) signals on a center conductor surrounded by a dielectric insulator, a braided or foil shield, and an outer jacket. The shield provides a return path for the signal and blocks external interference — the key structural difference from twisted-pair Ethernet, which uses differential signaling instead. Coax is used for cable TV distribution, DOCSIS broadband (cable internet), antenna connections, satellite, and legacy 10BASE2 Ethernet. Understanding coax types matters when installing or troubleshooting cable TV/internet, antenna systems, or retrofitting older coax-wired buildings.
Common Coaxial Cable Types
| Type | Impedance | Common Use | Connector | Notes |
|---|---|---|---|---|
| RG6 | 75 Ω | Cable TV, DOCSIS internet, satellite, antenna | F-type | Current standard for residential cable and satellite; thicker dielectric than RG59 reduces signal loss at higher frequencies |
| RG6 Quad Shield | 75 Ω | Satellite (especially DirecTV/Dish), long runs | F-type | Four shielding layers instead of two; required for satellite because satellite IF frequencies (950–2150 MHz) are more susceptible to interference than cable TV frequencies |
| RG59 | 75 Ω | Legacy CATV, analog video, CCTV cameras | F-type or BNC | Thinner and more flexible than RG6; higher signal loss per foot at high frequencies; should not be used for DOCSIS 3.0/3.1 or satellite |
| RG11 | 75 Ω | Long underground runs, CATV trunk lines | F-type | Much lower loss than RG6 per foot; stiffer and harder to terminate; used when a single run exceeds 150–200 feet where RG6 loss would be excessive |
| RG58 | 50 Ω | Legacy 10BASE2 Ethernet, CB radio, amateur radio | BNC | 50 Ω impedance — not compatible with 75 Ω cable TV or satellite systems; mixing impedances causes signal reflections |
| LMR-400 / LMR-600 | 50 Ω | Cellular boosters, Wi-Fi antenna runs, commercial radio | N-type, SMA | Very low loss per foot; thick and stiff; the correct choice when running an antenna cable longer than 20–25 feet for Wi-Fi or cellular booster installations |
F-Type Connectors and Termination Quality
Most residential coax uses F-type connectors. Termination quality has a disproportionate effect on signal quality — a poorly crimped or hand-twisted connector creates impedance discontinuities, signal reflections, and ingress (outside signals leaking in) that degrade DOCSIS modems and cause channel bonding failures. The correct tool is a coax compression tool with the matching compression F-connector for the cable's RG type; crimp connectors are second-best; hand-twist connectors should not be used for any data or signal application.
BNC connectors are used in 50 Ω applications (legacy Ethernet, test equipment, some professional video) and in CCTV installations. N-type connectors appear on outdoor antenna and cellular booster equipment where weatherproofing and low-loss connections matter.
Signal Loss and Run Length
Coax introduces signal loss (attenuation) that increases with frequency and cable length. At 1 GHz (approximately the upper end of DOCSIS 3.0 channel spectrum), RG59 loses roughly 10 dB per 100 feet, RG6 loses about 6 dB per 100 feet, and RG11 loses about 3.5 dB per 100 feet. DOCSIS systems have a usable signal range at the modem of roughly -7 to +7 dBmV for downstream. If a long run or too many splitters push the signal outside this range, the modem will bond fewer channels or fail to maintain a stable connection.
Splitters divide signal power between outputs and should be used only where necessary. A two-way splitter subtracts approximately 3.5 dB from each output; a four-way splitter subtracts approximately 7 dB. Every unnecessary splitter reduces the signal budget available for cable length.
Frequently Asked Questions
Can I use RG59 cable for cable internet?
You should not. RG59 was adequate for analog cable TV, but DOCSIS 3.0 and 3.1 modems use much higher frequencies (up to 1.2 GHz for DOCSIS 3.1 OFDM channels), where RG59's higher attenuation per foot significantly reduces the signal budget. On short runs (under 10–15 feet) RG59 may work, but for any in-wall run, replace with RG6. A modem connected via long RG59 may show low downstream power levels, fewer bonded channels than the ISP delivers, or complete inability to connect at full DOCSIS speeds.
How do I know if coax signal quality is causing my internet problems?
Log into your cable modem's status page (typically at 192.168.100.1) and check the downstream signal level, upstream power level, and SNR (signal-to-noise ratio) for each bonded channel. Downstream levels outside the range of -7 to +7 dBmV, upstream levels above 48–50 dBmV, or SNR below 33 dB on downstream channels all indicate signal quality problems. These numbers change when you swap cables, move splitters, or have the ISP adjust the signal level at the tap — they are the direct diagnostic output for coax signal problems.
When does RG11 make sense over RG6?
RG11 is worth the additional cost and installation difficulty when a single coax run exceeds about 150 feet (45 meters) and the run cannot be shortened. Common scenarios: a long underground run from a utility entry point to a remote building, a very long attic run across a large home, or a commercial installation where a single trunk feeds a distant distribution point. RG11 is stiff and requires special connectors and a heavier compression tool — it is not suitable for runs with tight bends or frequent connector access. If a run is under 150 feet, RG6 is the correct choice.