Coaxial / Twisted-pair / Ribbon Cable
Cable
Signal cables with geometry: coax shields one conductor for RF, twisted pair cancels noise differentially (Ethernet, RS-485), ribbon carries many lines to IDC connectors. Impedance matching is what separates them from 'just wire'.
What it looks like
Coaxial / Twisted-pair / Ribbon Cable
A typical cable — exact shape, colour and markings vary between manufacturers.
Types & variants
Key specs
Characteristic impedance
Ω50 Ω (radio/test gear) or 75 Ω (TV/video) — mismatches reflect.
Attenuation
dB/100mLoss rises with frequency; thick coax loses less.
Shield coverage
%Braid + foil percentage — how well noise stays out.
Category / bandwidth
MHzCat5e = 100 MHz, Cat6 = 250 MHz for network pairs.
Markings
Type printed along the jacket every metre (RG-6/U, CAT6 UTP 23AWG...).
Standard values
RG-58 for 50 Ω bench work, RG-6 for TV/satellite, Cat6 for Ethernet, 10/16/40-way ribbon.
How to choose
Match impedance to the system first (never mix 50/75 Ω casually), then loss over your run length, then connectors you can actually terminate (BNC/F/RJ45/IDC).
Pinout & package
Coax terminates in BNC/SMA/F connectors; twisted pair in RJ45 (T568B); ribbon presses into IDC headers — pin 1 marked by the red stripe.
Example circuits
- RG-58 + BNC from a function generator to a scope
- RS-485 bus over one twisted pair with 120 Ω terminators
- Ribbon cable to a 40-pin Raspberry Pi header
Common failures
Broken centre conductor at the connector (intermittent!), crushed coax changing impedance, split pairs in badly-punched RJ45s, ribbon conductors cracked at the IDC edge.
How to test
Continuity end-to-end on centre and shield, then centre-to-shield for shorts. Network cable testers check pair mapping; a TDR (or a scope + pulse) finds the metre where the fault hides.
Substitutes
Within the same impedance family, thicker coax for longer runs. Cat6 works for RS-485 in a pinch — use one twisted pair, not two random wires.