Copper
Twisted pair and coax. Cheap, familiar, and still how most desks are wired.
Level: beginner
What is it?
Copper transmission uses electrical signals through conductors, commonly twisted-pair Ethernet and coaxial cable. Twisting helps reduce electromagnetic pickup and crosstalk; cable category, length, connectors, and environment determine supported modes.
Why does it matter?
Copper is economical and easy to terminate for many local connections, but it has distance limits and can be affected by interference, poor termination, and cable damage.
Mental model
Bits are encoded as voltage/current changes and interpreted by a transceiver at the other end. The receiver depends on signal quality and timing, so wiring quality matters as much as the nominal standard.
How it works
- Twisted-pair Ethernet standards specify cable categories, link rates, and channel length assumptions.
- Poor terminations, split pairs, tight bends, and damaged conductors can cause errors or lower negotiated link rates.
- Coaxial cable uses a central conductor and shielding and is common in RF and cable access systems.
- Power over Ethernet can deliver power over supported twisted-pair links with compatible equipment and limits.
- Copper is electrically conductive between endpoints in ways that can introduce grounding and surge considerations.
Steps
- Select cable category and length for the target Ethernet standard.
- Terminate to the correct wiring scheme and verify connectors and pair integrity.
- Check negotiated speed/duplex and error counters at the link endpoints.
- Replace or certify the run if errors, attenuation, or pair faults persist.
Real-world usage
- Wiring offices, access switches, PoE cameras, and Wi-Fi access points.
- Diagnosing a link that negotiates at a lower speed or reports CRC errors.
Common mistakes
- Exceeding the standard's channel length or mixing unsupported components.
- Assuming a cable works correctly because carrier comes up.
- Confusing shielded copper with optical immunity to electromagnetic interference.
Interview questions
Why twist Ethernet cable pairs?
Twisting helps reject electromagnetic interference and reduce crosstalk between pairs.
What can cause an Ethernet link to negotiate below its target rate?
Cable category/length limits, pair damage, poor terminations, bad connectors, or endpoint configuration/capability mismatch.