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Electrical cable length
Quarter- and half-wave lines using the cable’s velocity factor.
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Formula & context
L¼ = c · VF / (4f); L½ = 2 L¼
A wave travels more slowly in a dielectric than in vacuum. Use the velocity factor of the exact cable, which is distinct from an antenna-wire shortening factor.
A worked example
145 MHz and VF = 0.66 give a quarter-wave line of approximately 34.1 cm.
Assumptions & limits
Connectors, attachments and end effects alter effective length. Tune a narrowband matching line with suitable measurement equipment.
Coaxial cable: loss and electrical lengthUnderstand the reasoning →From reading to experimenting
Electrical cable length
145 MHz and VF = 0.66 give a quarter-wave line of approximately 34.1 cm.
Open example with starting values →Frequency: 145 MHz · Velocity / shortening factor: 0.66 Back to the learning article →Then change exactly one value. Compare the result and use the formula to explain why it changes. The model limits below the calculator also apply here.