Antenna & Radio Calculators
HAM-Tools comes with 37 calculators and tools straight from radio practice — all native SwiftUI, no webview, with live charts where it makes sense and short Markdown descriptions per calculator (tip button in the form header).
In the sidebar on the left under "Calculators" you'll find them grouped:
Wire Antennas
| Calculator | Purpose |
|---|---|
| Dipole | λ/2 half-wave dipole with velocity factor, insulated/bare, all bands |
| Groundplane / Vertical | λ/4 with radials (2–4 of them), stacking factor per build |
| J-Pole / Slim Jim | End feed with stub matching, popular portable antenna |
| Double Bazooka | Coax choke right at the feed point |
| Windom / OCFD | Off-center-fed dipole with 4:1 or 6:1 balun |
| EFHW Antenna | End-Fed Half-Wave with 49:1 transformer, multiband variant |
| EFHW Shortening | Coil shortening for a portable EFHW |
| Loop Antenna | Full-wave loop or λ/2 loop, vertical/horizontal |
| Trap Dipole 🆕 | 2-band dipole with traps — resonant L↔C, reactance, coil turns (Wheeler), wire lengths inner/outer |
Directional Arrays
| Calculator | Purpose |
|---|---|
| Moxon Rectangle | 2-element beam, compact, broadband — Cebik W4RNL MoxGen polynomials, wire-diameter-dependent |
| HB9CV Beam | 2-element phased array per the HB9CV original with gamma-match design (inner-conductor Ø, spacing, trimmer C) |
| Hexbeam | 6-band G3TXQ Hexbeam, WiMo HEX6B-compliant, band-specific table (20/17/15/12/10/6 m) |
| Yagi Calculator | 3–7 element Yagi with reflector + directors |
| Spiderbeam Single-Band | Wire cross per band — flat mode or V shape with spreader half-arm length |
| Spiderbeam Multi-Band | Multiband wire cross 20-17-15-12-10 m, DF4SA build guide v2.20 |
Special Antennas
| Calculator | Purpose |
|---|---|
| Magnetic Loop | Capacitor + loop area, Q factor, bandwidth |
Coils & Transformers
| Calculator | Purpose |
|---|---|
| Balun / Unun | Voltage and current symmetry with a transformer (1:1 / 4:1 / 9:1) |
| Common-Mode Choke | Common-mode choke with ferrite, number of turns |
| Element Lengthening Coil | Shortening/lengthening coil for mobile antennas |
| Coil Winder | Air coils, wire diameter, number of turns, inductance |
| Reactance & LC Resonance 🆕 | X_L and X_C at a frequency, resonant frequency f = 1/(2π√LC), matching resonance partner for L or C |
Matching & Lines
| Calculator | Purpose |
|---|---|
| L-Network Matching | L-match with two elements, high-pass/low-pass variant |
| ATU Wire Calculator | Optimal wire lengths for automatic antenna tuners (JC-4, SG-230, AH-730, CG-3000) — avoids half-wave resonances |
| Coax Stub | λ/4 or λ/2 stub matching with characteristic impedance |
| Cable Loss | Loss per 100 m at the desired frequency, standard-cable dB |
| λ/4 Transformer 🆕 | Q-section: Z₀ = √(Z₁·Z₂), physical length λ/4 · VF, SWR comparison with/without transformer |
| Ladder Line / Twin-Lead 🆕 | Characteristic impedance Z₀ = (120/√εr)·arccosh(D/d), velocity factor, approximation formulas for common lines |
Signals & Tools
| Calculator | Purpose |
|---|---|
| Level Converter | dBm ↔ dBW ↔ W ↔ V ↔ S-units |
| SWR Simulator | Reflection coefficient, return loss, VSWR visualization |
| Link Budget / Range | Radio-path calculation with path loss |
| Radio Horizon / Line of Sight 🆕 | Quasi-optical VHF/UHF range d = 3.57·√k·√h with refraction factor — antenna heights of both stations |
| QTH Locator | Maidenhead ↔ geo coordinates, distance/bearing |
| Smith Chart | Interactive Smith chart with matching paths |
| Antenna Simulator | Web NEC2 simulator (nec2c.wasm in the browser), 14 templates (Dipole, Yagi 2/3/5, EFHW, Windom, Groundplane, Moxon, Delta Loop, Quad, Inverted-V, HB9CV, Spiderbeam 20m, Hexbeam 20m) — also live at toolbox.funkwelt.net/antennensim |
Station & Safety 🆕
New in 1.12.0
Three calculators around station operation and safety — added in version 1.12.0 together with five more new antenna/line calculators.
| Calculator | Purpose |
|---|---|
| RF Exposure | Safety distance per ICNIRP 1998 (occupational + general public) — E/H field limits, EIRP, average power with duty cycle |
| Battery Runtime | Operating time from capacity, RX/TX current, and TX share — presets for LiFePO₄, lead AGM, Li-Ion, NiMH including usable depth of discharge |
| DC Voltage Drop | Voltage loss on the 12 V supply line: R = 2·L/(κ·A), power dissipation, cross-section recommendation per current |
Antenna Simulator: NEC2 Engine in Detail
Greatly expanded in 1.11.0
The simulator computes with real NEC2 (nec2c as WASM) and since 1.11.0 delivers considerably more than gain + SWR:
- Pattern metrics: elevation angle of the main-lobe maximum, front-to-back ratio (F/R) and −3 dB beamwidth in azimuth and elevation — right below the chart
- Ground catalog: 8 ground types from free space through salt water, fresh water, farmland, loam, dry/urban, desert to the perfect reflector — the difference in radiation angle is instantly visible
- Height slider: change the build height above ground live and watch the effect on elevation angle + gain
- SWR over band: one-click sweep across the band edges → bandwidth visualization as a curve
- Plausibility warnings: segment length vs. λ, wire radius, feed/load segment validity are checked before the run — typical NEC2 modeling errors show up immediately
The "Open in Simulator" buttons of the antenna calculators (Dipole, Yagi, Moxon, HB9CV, EFHW, Magnetic Loop, Hexbeam …) hand over the finished wire model including the matching capacitor or lengthening coil.
Sim export fix in 1.11.0
On Yagi, HB9CV, and Moxon the velocity factor was applied twice before 1.11.0 — the sim models were ~5 % too long and showed barely any directivity. Since 1.11.0 resonance and F/R are correct (Yagi e.g. ~27 dB instead of 3 dB). On Magnetic Loop and EFHW the capacitor or coil is now carried into the model.
Consistent Operating Concept
Every calculator has the same layout:
- Inputs left/top — frequency, material parameters, geometry
- Results right/bottom — live update on every input, no "Calculate" button needed
- Chart / visualization where it makes sense (Smith chart, SWR curve, element geometry, coil cross-section)
- Material selection where relevant (wire diameter AWG/CCS, coax type RG-58/RG-213/H2000, coil form)
- Info button in the form header opens the Markdown docs per calculator with background + formula + practical recommendations
Web Variant
The main calculators are also available at toolbox.funkwelt.net as a web app — same engine, Vue 3 UI, ideal for mobile use in the field or for a quick lookup on the smartphone. The eight new 1.12.0 calculators are available there too. The macOS app is more capable feature-wise (more calculators, Smith chart, antenna sim, logbook integration).
Moxon: Math Fix Against Cebik W4RNL
Correction since 1.10.7
The earlier constants (A = 0.475 λ etc.) produced an antenna that was about 24 % too long (resonance at 11.4 MHz instead of 14.2 MHz). Since version 1.10.7 the Moxon calculator uses the Cebik MoxGen polynomials (wire-diameter-dependent, x = log₁₀(d/λ)) — verified against the Cebik wire-Moxon table for #14 Cu wire. Material picker: 2 mm wire or 12 mm aluminum tube.
ATU Wire Calculator: Avoiding Resonances
New since 1.10.7
Automatic antenna tuners (JC-4, SG-230, AH-730, CG-3000) fail at wire lengths near a half-wave resonance — the impedance jumps to several kΩ there and lies outside the match range. The ATU Wire Calculator shows you the problematic lengths per band as red zones and suggests safe consensus ranges (typically 23-28 m and 46-50 m for tuners with a 10 m–60 m match range). Input: desired length, velocity factor; output: a visual ruler with resonances, tuner comparison, antenna recommendations, counterpoise hints.
Hexbeam: G3TXQ Compliance
Verification June 2026
The Hexbeam calculator was implemented from the official WiMo EAntenna HEX6B build guide (G3TXQ license, Rev. V2.1) and topologically corrected by HB9EIZ. Since 1.12.0 the turning radius uses the real G3TXQ value (0.1539 · λ). Real-world verification on the actual WiMo HEX6B build together with HB9EIZ is planned for June 2026 — results will feed into a possible model re-tuning.
Hexbeam in the simulator: real G3TXQ geometry since 1.11.1
"Open in Simulator" for the Hexbeam no longer loads the earlier approximation geometry (which radiated almost bidirectionally), but the tuned G3TXQ wire run from the original EZNEC model: W-shaped driven element with center feed + U-shaped reflector, λ-scaled per band. NEC-verified resonant on all bands (~1.7 SWR) with clear directivity (~10.5 dB F/R on 20 m over real ground).
More Detail
The detailed calculator descriptions with formulas, sources, and practical recommendations are available in the app per calculator (info icon in the form header). This page here is intentionally kept brief — a dedicated web doc per calculator will come in a later iteration.