RF Coax Cable Loss Calculator: dB Loss and the Noise Figure It Actually Costs You

Posted by GPIO Labs on August 20, 2026

RF Coax Cable Loss Calculator

RF Cable Loss

Coax Cable Loss Calculator

Cable loss doesn't just waste power — before an LNA, it adds directly to your system's noise figure, dB for dB. This calculator shows both: total loss for your run, and what that loss actually costs your receive chain depending on where your LNA sits.

Cable & Run

Cable type

Frequency (MHz)

Cable length

Include connector loss (2 connectors, ~0.15 dB each)

Total Loss

0.00 dB

LMR-400 · 433 MHz · 50 ft

Cable loss (no connectors) —

Connector loss added —

Power remaining at far end —

Loss per 100 ft at this frequency —

System Impact: Where Should the LNA Go?

A passive cable's noise figure equals its loss in dB. Put it in front of your LNA and that loss adds straight to your system noise figure. Put your LNA at the antenna end instead, and this same cable segment barely matters — it's now attenuating an already-amplified signal.

LNA noise figure (dB)

LNA gain (dB)

LNA AT THE RECEIVER END

— dB

System noise figure — cable loss hits before any gain

LNA AT THE ANTENNA END

— dB

System noise figure — cable loss comes after the LNA's gain

Attenuation modeled as A₁√f + A₂f per manufacturer datasheets (Times Microwave LMR series for LMR-100/195/240/300/400/600/900; Belden 8259/9258/8267 for RG-58/RG-8X/RG-213). System noise figure computed via the Friis cascade formula treating the cable as a passive lossy stage. Connector and system-impact figures are planning estimates — verify against your actual components for critical link budgets.