Feedline Lab — Feedline Loss & RF Power Suite
100% client-side — your data never leaves the browser13 cable types, datasheet figuresMetric + imperial
How much of your transmitter power actually reaches the antenna? This free suite answers it six ways: a coax loss calculator with 13 cable types (LMR-400, RG-213, 9913, 1/2" HELIAX and more, figures from manufacturer datasheets), a cable chooser that ranks cables by your band, length and budget, a dBm ↔ watts converter (with volts and dBµV), an S-unit converter, an ERP/EIRP calculator, and a printable coax loss chart across all ham bands.
Coax loss calculator
How the numbers are computed
Coax loss. Each cable stores its manufacturer’s nominal attenuation points (dB per 100 ft). Values between published points are interpolated on a log-log scale — the standard practice since coax loss follows roughly the square root of frequency plus a dielectric term. Frequencies outside a cable’s published range show “—”: we never extrapolate beyond datasheet data. dB per 100 m = dB per 100 ft × 3.28084 (check: LMR-400 at 150 MHz is 1.5 dB/100 ft = 4.92 dB/100 m on the Times datasheet).
SWR-adjusted loss. With matched loss A dB and load reflection ρ = (SWR−1)/(SWR+1), total system loss = 10·log₁₀((a − ρ²/a) / (1 − ρ²)) where a = 10^(A/10). This is the exact transmission-line result: it reduces to the matched loss at SWR 1:1 and to zero for a lossless line at any SWR. Connector pairs add as lumped loss (default 0.1 dB each, editable).
Power & S-units. dBm = 10·log₁₀(P in mW); P(W) = 10^((dBm−30)/10); dBW = dBm − 30. Vrms = √(P·R). S-meter: HF S9 = −73 dBm (50 µV at 50 Ω), VHF/UHF S9 = −93 dBm per IARU Region 1, 6 dB per S-unit; readings above S9 are reported as S9+dB.
ERP/EIRP. ERP(W) = P_tx · 10^((G_dBd − L)/10); EIRP = ERP + 2.15 dB (dipole gain over isotropic).
Sources. Attenuation tables: Times Microwave Systems LMR-240/400/600 datasheets; Belden 8240 (RG-58), 9258 (RG-8X), 8241 (RG-59), 1694A (RG-6), 8267 (RG-213), 9913 datasheets; Belden CDT RG-214 datasheet; L-com RG316/U datasheet; M17/128-RG400 per MIL-C-17; CommScope/Andrew LDF4-50A datasheet. Prices in the chooser are approximate typical US ham-retail per foot, for comparison only.