Best Practices for Using Coax Cables: Installation, Termination & Performance

Overview: Why Coax Still Matters

Coaxial cable remains a common choice for RF, CCTV, satellite, analogue video, and some audio applications because it combines a predictable impedance, shielding against interference, and relatively low cost. This guide covers best practices for selecting, installing, and testing coax cable to reduce loss, reflections, and long-term problems. The keyword "best practices for using coax cables" is used throughout to help you find practical methods and checks for reliable installations.

Common coax types and when to use them

Choose a coax type to match frequency, run length, and required flexibility. Short runs at VHF/UHF may use thinner cable; longer runs or higher frequencies need low-loss variants.

In South Africa, availability and lead times vary; popular brands and types are often in stock at national distributors and maker stores, but specialised low-loss types (e.g., LMR variants) may need ordering. Factor local stock and delivery when planning projects.

Basic electrical checks and formulas

Key electrical concerns are attenuation (loss), impedance matching, and power handling. Use these simple relations when sizing runs:

• Attenuation over length: Loss(dB) = alpha (dB/m) x length (m). Choose alpha from cable datasheet.
• Power in dBm: P(dBm) = 10 x log10(P(mW)). Use to check transmitter power vs cable loss.
• Return loss / VSWR: VSWR~(1+||)/(1-||) where is the reflection coefficient from impedance mismatch.

Example: a 20 m RG6 run with alpha~0.2 dB/m gives Loss = 0.2 x 20 = 4 dB. If a transmitter outputs 20 dBm, received level reduces by 4 dB (ignoring connectors and other losses).

Mechanical and environmental installation tips

Good mechanical practice reduces long-term failures. Consider these points:

• Bend radius: Never bend coax tighter than the manufacturer's minimum; a common rule is 10x cable diameter for flexible types and 4x for rigid coax.
• Secure supports: Use cable ties and clips to avoid strain at connectors and to prevent chafing where runs pass through walls.
• Outdoor runs: Use UV-resistant, weatherproof jacketed cable and protect terminations with appropriate sealing (self-amalgamating tape or weather boots).
• Avoid coiling excess cable tightly; use figure-8 or large-diameter loops to store slack without inducing twists.

Termination and connector best practices

Proper termination is crucial for impedance continuity. Match cable impedance to connectors (50 Ohm cable with 50 Ohm connector, 75 Ohm with 75 Ohm). Clean conductor and dielectric before crimping or soldering, and use the correct tool for each connector type.

Sample BNC crimp and solder wiring (50 Ohm)

Coax end view (simplified):
  Outer braid -----|||||-----\  <-- shield to connector body
                      |      \
                      |       \-- centre pin (inner conductor)
  Dielectric -------  O

When assembling, trim the braid to avoid stray strands touching the centre conductor. Verify continuity and insulation resistance after termination.

Testing, troubleshooting and common faults

Testing ensures that installations meet expected performance. Recommended checks:

• Continuity check: Confirm centre conductor and shield continuity with a DMM (low-resistance path).
• Return loss/VSWR test: Use an antenna analyser or VNA for RF links; low return loss indicates good matching. For CCTV/analogue video a simple signal-level check with the camera and monitor can reveal major issues.
• Power loss estimate: Subtract total cable and connector loss from transmitter power to confirm the receiver still meets sensitivity needs.

Common faults include loose or corroded connectors, damaged dielectric causing impedance changes, and water ingress in outdoor terminations. In South Africa's coastal or high-humidity areas, prioritise sealed connectors and weather protection to avoid corrosion over months/years.

Accessory and compatibility notes

Buy compatible connectors, crimp tools, and test gear. For CCTV: RG59/RG6 with BNC connectors is common. For RF antennas: 50 Ohm cable and N-type or SMA connectors are typical. When mixing connector genders or impedances, use purpose-made adapters and expect additional loss and potential mismatch.

Troubleshooting checklist

• No signal: Check center conductor continuity, then shield continuity, then connector seating.
• Weak signal on long runs: Calculate expected loss and compare to measured; consider an amplifier or lower-loss cable.
• Intermittent noise: Inspect for moisture ingress, crushed cable, or loose connectors.

Sources

• CableOrganizer: Coaxial Cable Basics and Installation Guides
• RFNow: Understanding Coaxial Cable Characteristics
• Transmission Line Handbook (practical reference)
• Communica: Connectors, Wire & Cable category (stock & brands)

This guide emphasises field-proven practices for coax installations used by South African makers, students, technicians, and engineers. Use manufacturer datasheets for precise loss coefficients, power ratings, and bend-radius limits; local stock and pricing are subject to change, so verify availability with your supplier and plan for possible lead times.