Coax Loss & Power Out
Total cable loss from the per-100-ft spec, and what actually reaches the antenna.
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The engineering
Datasheets quote dB per 100 ft at each frequency; loss scales linearly with length and the percentage row makes it visceral — 3 dB of coax quietly eats half your transmitter. RG-58 at 915 MHz runs ~23 dB/100 ft; LMR-400 about 3.9.
Receive side hurts identically: cable loss ahead of the LNA adds straight to noise figure (see the cascade card).
Where this math comes from
Oliver Heaviside patented the coaxial line in 1880 — concentric conductors to keep the signal in and the world out — decades before anything needed it. Espenschied and Affel's 1929 Bell patent made it broadband transmission plumbing, and WWII radar plus postwar TV built the connector-and-cable industry we buy from.
The dB/100 ft spec convention is pure Bell practice: loss as money, priced by the foot.
- 1880Oliver HeavisideCoaxial cable patented.
- 1929Espenschied & AffelBroadband coax system — the modern cable.
- 1943Wartime radar industryStandardized RG-series cables and connectors.
See the full timeline of the math behind every calculator →
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