Ham Radio Math Toolkit

This toolkit provides a collection of antenna, RF, and related calculators in a free, browser-based interface. It is designed to support common amateur radio calculations, including frequency, wavelength, impedance, and antenna-related measurements, in a format that is fast and practical to use.

Many of these calculations are typically spread across separate tools, reference tables, or manual formulas. This toolkit brings them together into a consistent, structured set of utilities that can be accessed and used directly without switching between resources.

All calculations run locally in your browser, with no external dependencies, allowing for quick evaluation and repeated use in real-world operating, design, or troubleshooting scenarios.

Antenna lengths

Common "starting point" wire lengths. Use the shortening factor to account for end-effect / insulation / environment.

Formulas
Uses classic ham constants in feet:
Half-wave dipole (total) ~= 468 / f(MHz)
Quarter-wave ~= 234 / f(MHz)
Full-wave loop circumference ~= 1005 / f(MHz)
Then multiplies by the shortening factor.
Coax electrical length

Compute physical length for a desired electrical length (degrees or wavelength fraction) using velocity factor (VF).

Mode
Formulas
lambda (in coax) = (c / f) * VF
Length = lambda * (degrees/360) or lambda * fraction
c = 299,792,458 m/s
Coax loss

Uses embedded attenuation tables (typical) from manufacturer datasheets. Interpolates between points.

Free-space path loss (FSPL)

Quick sanity check for links (real-world paths also include polarization, terrain, clutter, antenna patterns, fade margin, etc.).

Power & dB

Convert W <-> dBm/dBW, compare two power levels, and convert dBd <-> dBi.

Power conversion
dB difference DeltadB = 10*log10(P2/P1)
Formulas
dBm = 10*log10(P(W)*1000)
dBW = 10*log10(P(W))
P(W) = 10^(dBm/10) / 1000
VRMS = sqrt(P*Z)
Vpp = 2*sqrt2*VRMS
dBi = dBd + 2.15
Quick band picker

Pick a common ham band center frequency, then push it into the calculators.

You can still override any field per-tool.
Reactance & resonance

Handy for LC networks, traps, and "why is my tuner doing that?" moments.

Formulas
XL = 2pifL
XC = -1/(2pifC)
f0 = 1/(2pisqrt(LC))
(Use f in Hz, L in H, C in F.)
SWR / Return loss

Two ways: (1) forward/reflected power (wattmeter), or (2) load impedance vs Z0.

Mode
Formulas
|Gamma| = sqrt(Pref/Pfwd)
SWR = (1+|Gamma|)/(1-|Gamma|)
Return Loss (dB) = -20*log10(|Gamma|)
Mismatch Loss (dB) = -10*log10(1-|Gamma|^2)
Gamma = (ZL - Z0)/(ZL + Z0)
Sources

Coax loss/VF values embedded on this page are pulled from these public datasheets (typical values; always verify your exact part / revision):

General formulas (SWR, dB conversions, FSPL, reactance) are standard RF engineering relationships commonly found in ARRL handbooks and basic EM references.