A coaxial cable (“coax”) is a round, layered transmission line used to carry high‑frequency electrical signals with low loss and noise. Its cross‑section has:

• Center conductor (solid or stranded copper)
• Dielectric insulator (foam or solid polymer)
• Outer conductor/shield (metal braid and/or foil)
• Protective jacket

“Coaxial” means the conductors share the same axis. This geometry confines the electromagnetic field between the inner conductor and shield, enabling transverse electromagnetic (TEM) wave propagation. The shield serves as the return path and blocks external interference while limiting the cable’s own radiation.

Operation hinges on characteristic impedance (typically 50 Ω for RF/telecom, 75 Ω for video/CATV). The dielectric’s permittivity and the conductor diameters set impedance, capacitance, and velocity factor (signal speed relative to light). Proper impedance matching and termination prevent reflections and standing waves (low VSWR). Losses increase with frequency due to skin effect and dielectric/conductor attenuation; better materials, larger diameters, and smooth surfaces reduce loss.

Common connectors: F-type (TV), BNC (test/CCTV), N and SMA (RF/microwave). Variants include RG-6 (75 Ω) and RG-58/LMR (50 Ω).

Uses: cable TV, satellite feeds, broadband modems, antennas, radios, CCTV, test equipment. Pros: excellent shielding, predictable impedance, wide bandwidth, easy connectors. Cons: heavier than twisted pair, higher cost per meter, and rising attenuation over long runs/high frequencies (fiber often preferred for very high data rates or distances).

• RG59 (75 Ω)

  • Cable: Thinner center conductor, smaller diameter, higher attenuation.
  • Typical uses: Short-run baseband video (analog CCTV), legacy composite/component video, BNC patch leads, short in-rack interconnects. Solid copper versions preferred for baseband video.
  • Not ideal for modern satellite/cable internet or long RF runs due to loss at higher frequencies.

• RG6 (75 Ω)

  • Cable: Most common for RF distribution; moderate diameter; available in dual/tri/quad-shield; center conductor often copper-clad steel (CCS) for tensile strength, or solid copper for DC power/tone.
  • Typical uses: Cable TV (CATV), satellite TV (LNB feeds), OTA antenna feeds, cable internet (DOCSIS), general home distribution up to ~1–3 GHz. Quad-shield for noisy/urban environments; flooded/direct-burial and UV-rated jackets for outdoors.
  • Sweet spot for residential runs up to ~150–200 ft.

• RG11 (75 Ω)

  • Cable: Thicker, lower attenuation, larger bend radius, harder to terminate; uses F11-size connectors.
  • Typical uses: Long backbone runs for CATV/satellite/OTA where distance would overly attenuate RG6; building risers, campus feeds, lengthy drops to pedestal. Common when runs exceed ~150–200 ft or where signal margin is tight.

Additional notes

• Attenuation at ~1 GHz (per 100 ft, approximate): RG59 ≈ 7–8 dB; RG6 ≈ 5–6 dB; RG11 ≈ 3–4 dB.
• Jackets/ratings: CMP (plenum), CMR (riser), CM/CMX (general/UV/outdoor); pick based on code and environment.
• Connectors: F-type for CATV/satellite (RG6/RG11); BNC common on RG59 for CCTV.
• For satellite/LNB power or MoCA, prefer solid copper center conductor; use quad-shield in high-interference areas.

• Impedance: 50 Ω is the standard for most RF transmit/receive systems; 75 Ω is the standard for video, broadcast, and CATV.
• Design rationale: ~30 Ω gives maximum power handling; ~77 Ω gives minimum loss. 50 Ω is a compromise between power handling and loss; 75 Ω is closer to minimum-loss for air/foam dielectrics.
• Loss: For similar size and quality, 75 Ω tends to have slightly lower attenuation per unit length, especially at high frequencies. Actual loss depends on specific cable type.
• Power handling: 50 Ω generally handles higher transmit power safely. 75 Ω is optimized for lower-power or receive-only distribution.
• Connectors: 50 Ω systems use N, SMA, 50 Ω BNC, TNC. 75 Ω systems use F-type, IEC, 75 Ω BNC. Mismatching connector types can add reflections.
• Mismatch effects: Connecting 50 Ω gear to 75 Ω cable (or vice versa) gives VSWR ≈ 1.5:1 (≈4% power reflected). Often fine for receive-only; risky for high-power transmitters. Use matching pads/transformers if you must mix.

Which to use: • Use 50 Ω for transmitters, two-way radios, ham, cellular/Wi‑Fi, test equipment, RF labs, antennas designed for 50 Ω.
• Use 75 Ω for TV/CATV, satellite LNBs, CCTV, long receive-only runs, and equipment specified for 75 Ω (e.g., many video/audio interfaces, SDRs with 75 Ω inputs).
• Always match the system’s specified impedance end-to-end. If unsure:
– Transmitting more than a few milliwatts → 50 Ω.
– Receive-only distribution or video → 75 Ω.
– Mixed systems → add proper impedance matching.

• Bandwidth:

  • Twisted pair (Ethernet copper): 100 Mbps–1 Gbps up to 100 m on Cat5e; 10 Gbps on Cat6/6A (55–100 m); Cat8 up to 25/40 Gbps but only ~30 m.
  • Coaxial: Very wide RF spectrum (hundreds of MHz). Practical data networking typically up to ~1–2.5 Gbps in consumer tech (MoCA 2.5, DOCSIS per home), higher in operator plant via channel bonding; not as scalable as fiber for point-to-point Ethernet.
  • Fiber: Highest—1/10/25/40/100/400+ Gbps per wavelength; multi-terabit with DWDM.

• Distance (without regeneration):

  • Twisted pair: Generally 100 m for 10/100/1G; 10GBASE-T 55–100 m (Cat6/6A); Cat8 ~30 m.
  • Coaxial: Tens to hundreds of meters depending on frequency and cable (e.g., CCTV/IF ~300–500 m). With amplifiers, kilometers in HFC, but point-to-point Ethernet over coax is uncommon.
  • Fiber: Multimode 10G ~300 m (OM3) to ~400 m (OM4); some MMF up to ~2 km at lower rates. Single-mode 10–80+ km (and far more with amplification).

• EMI immunity:

  • Fiber: Immune to electromagnetic interference; no crosstalk, no ground loops.
  • Coaxial: Very good immunity due to shielding; better than unshielded twisted pair; susceptible if shielding/terminations are poor.
  • Twisted pair: UTP relies on differential signaling—adequate in typical offices but vulnerable to strong EMI; STP/FTP improves immunity if properly grounded.

• Summary:

  • Bandwidth: Fiber > Coax ≥ High-grade twisted pair (short) > Older twisted pair.
  • Distance: Fiber > Coax > Twisted pair.
  • EMI immunity: Fiber > Coax > UTP (STP sits between coax and UTP, depending on implementation).

It depends on coax type, frequency, and acceptable loss (often ~3–6 dB “significant”). Typical, no-amplifier guidelines:

• Baseband/CCTV video (up to ~5–10 MHz):

  • RG-59: ~750–1000 ft (230–300 m)
  • RG-6: ~1000–1500 ft (300–450 m)
  • RG-11: ~2000–3000 ft (600–900 m)

• CATV/Satellite/MoCA (~50–2150 MHz):

  • RG-59: ~100–200 ft (30–60 m) at 1 GHz; shorter at >1.5 GHz
  • RG-6: ~150–250 ft (45–75 m) at 1 GHz; ~100–150 ft (30–45 m) at 2 GHz
  • RG-11: ~300–500 ft (90–150 m) at 1 GHz; ~200–350 ft (60–105 m) at 2 GHz

• RF/data examples (approx attenuation per 100 ft; halve length for ~6 dB budget):

  • RG-59: ~3 dB @100 MHz, ~10 dB @1 GHz
  • RG-6: ~2 dB @100 MHz, ~6–7 dB @1 GHz, ~10–12 dB @2 GHz
  • RG-11: ~1.5 dB @100 MHz, ~4–5 dB @1 GHz, ~7–9 dB @2 GHz
  • LMR-400 (50 Ω): ~1.3 dB @100 MHz, ~3.9 dB @1 GHz, ~6.8 dB @2.4 GHz

Rules of thumb:

• Higher bandwidth/frequency = shorter max run.
• For QAM/OFDM/digital links, keep total loss typically <10–15 dB without active compensation; <3–6 dB if you want generous margin.
• Use larger cable (RG-11/LMR-400), fewer connectors, and quality compression fittings to extend runs.
• For longer runs, add line amplifiers/equalizers (CATV), active baluns/extenders (CCTV), or move to fiber.

• F-type (75 Ω): TV/CATV/satellite over RG6/RG59. Best: compression or crimp; avoid twist‑on. Termination (compression):

  1. Cut square; strip 1/4" braid + 1/4" dielectric (6.35/6.35 mm). Leave foil on dielectric; fold braid back over jacket.
  2. Push connector until dielectric is flush with the post; center conductor protrudes ~1–2 mm.
  3. Compress with the correct tool/die for the connector/cable.
  4. Tighten to ~20 in‑lb (2.3 N·m). Weatherproof outdoors.

• BNC (50 Ω RF/test; 75 Ω broadcast) on RG58/59/6/179/316, etc. Available crimp, clamp, or solder/crimp. Use matching impedance. Termination (crimp):

  1. Slide ferrule on cable.
  2. Strip per datasheet (commonly ~3–4 mm center, ~6–7 mm braid). Do not nick strands.
  3. Fit crimp pin on center conductor; ensure conductor is visible through pin inspection hole; crimp with specified pin die.
  4. Insert pin into body until it clicks/locks.
  5. Splay braid over connector knurl; slide ferrule up; crimp with specified ferrule die.
  6. Bayonet mates with a quarter‑turn; no torque spec.

• N (50 Ω common; 75 Ω exists) for higher power/outdoor on RG8/213/LMR‑240/400, etc. Termination (crimp):

  1. Slide heat‑shrink and ferrule on first.
  2. Strip per datasheet (leave foil on dielectric; fold braid back).
  3. Crimp or solder the center pin as specified; verify pin length.
  4. Seat pin/body; ensure O‑ring in place; pull braid over knurl.
  5. Crimp ferrule with correct die; wrench the coupling nut to ~12–15 in‑lb (1.4–1.7 N·m).
  6. Weather seal (butyl + UV tape/boot).

General: match connector to cable size and impedance; use the right dies; avoid over‑stripping; no stray braid “whiskers.” Perform tug test; verify continuity (center‑to‑shield open) and, if RF critical, sweep/return‑loss check.

1. Benchmark and isolate

• Check modem/TV stats: downstream −10 to +10 dBmV (ideal −7 to +7), SNR > 35 dB; upstream 35–50 dBmV. QAM256 MER > 32 dB, low/zero uncorrectables.
• Inspect visually: kinks, crushed jacket, loose/corroded F-connectors, “stingers” (braid touching center).
• Bypass pieces: direct feed to modem/TV, then add components back one-by-one to locate loss.
• Tools: spectrum analyzer or meter (MER/SNR/BER), TDR/cable mapper for opens/shorts, continuity for shield, leakage detector outdoors.

2. Cabling and shielding

• Replace RG59 with RG6 (quad-shield for noisy environments). Maintain bend radius > 10× cable diameter.
• Use compression F-connectors; torque 30–40 in‑lb. Weatherproof outdoor connections; drip loops; replace corroded barrels/plates with 3 GHz-rated.
• Keep coax away from AC/motors; cross at 90°. Proper bonding to building ground.

3. Splitters and topology

• Prefer home-run star; minimize cascaded splitters. Use quality 5–1002/1218/1675 MHz splitters; terminate unused ports with 75 Ω caps.
• Understand losses: 2‑way ≈ 3.5 dB; 3‑way has one ≈ 3.5 dB leg and two ≈ 7 dB legs. Balance runs accordingly.
• For MoCA, install PoE filter at entry; use MoCA‑rated splitters (5–1675 MHz).

4. Amplification and levels

• Place low‑noise, bi‑directional amp at entry before splits; avoid amplifying upstream of the modem unless return‑path supported or use a modem bypass port.
• Don’t over‑amplify; add fixed attenuators to keep downstream near 0 dBmV and upstream < 50 dBmV. Use equalizers if high‑frequency tilt is excessive.
• Use LTE/5G ingress filters if off‑air leakage is suspected.

5. Common fixes

• Replace cheap/old splitters, damaged jumpers, RG59, and push‑on fittings.
• Tighten/retorque all connectors; remove corrosion and moisture.
• Terminate every unused port; eliminate daisy chains.
• If issues persist, have the provider check drop/tap, ingress, ground, and plant levels.