Calculators

Online tools for antennas, feedlines, matching networks, filters, oscillators and everything around them. Each calculator is its own page, with the formulas, a drawing, and an honest statement of where it stops being valid.

The list is built from the pages themselves, so it is always complete and never drifts out of step with the navigation.

Total: 108

Antenna calculators

Flower Pot antenna calculator

Dipole leg lengths, the length of cable for the choke, and the resonance and velocity factors.

Ground Plane antenna calculator

The length of the radiator and of the radials.

J-pole antenna calculator

The dimensions of a J-pole, with the resonance and shortening factors applied.

Yagi antenna calculator (DL6WU)

Element dimensions with the boom correction and the way the elements are mounted taken into account.

Kharchenko (BiQuad) antenna calculator

Dimensions from the frequency, the impedance and your choice of units.

Log-periodic antenna calculator (LPDA)

The dimensions of a log-periodic directional antenna for a wide frequency range.

Dipole and Inverted-V calculator

Online half-wave dipole and Inverted-V calculator: leg length corrected for conductor thickness, feedpoint impedance as a function of height, and the SWR to expect.

Magnetic loop calculator

Online small transmitting loop calculator: tuning capacitance, efficiency, Q, bandwidth, loop current and the voltage across the capacitor.

Loaded vertical calculator

Online calculator for a shortened vertical with a loading coil: the inductance for base, centre and 2/3 height, the radiation resistance, the efficiency and the effect of a capacitance hat.

Full-wave loop calculator

Perimeter, side length, feedpoint impedance, polarisation and the quarter-wave transformer.

Receive loop calculator

Online receive magnetic loop calculator: the inductance of a multi-turn loop, the tuning capacitance, the effective height, the induced EMF and the Q of the tuned circuit.

Capacitance hat calculator

Online capacitance hat calculator for a shortened antenna: the capacitance of a disc or a spoked ring, how much smaller the loading coil becomes, and how the radiation resistance rises.

Radial system calculator

Online estimate of a radial system for a vertical: ground loss resistance against the number and length of radials, antenna efficiency, and the shortfall against the reference 120 radials.

Coaxial trap calculator

Online coaxial trap calculator for a multiband dipole: number of turns, inductance, capacitance, resonant frequency and the voltage across the trap.

EFHW and 49:1 transformer calculator

Online EFHW antenna calculator: half-wave wire length, counterpoise, and a check that the 49:1 transformer has enough inductance on the ferrite core you chose.

Random wire length calculator

Online search for a random-wire antenna length to use with a 9:1 unun: lengths that avoid a multiple of a half wave on every band you select.

Helical antenna calculator

Online axial-mode helical antenna calculator: helix diameter and pitch, gain from Kraus, beamwidth, feedpoint impedance and axial ratio.

Parabolic dish calculator

Online parabolic dish calculator: gain, beamwidth, focal length, depth, illumination angle and the tolerance on surface accuracy.

Patch antenna calculator

Online microstrip patch antenna calculator: patch width and length, effective permittivity, the feed point for 50 Ω, and the bandwidth on FR-4 and Rogers.

Waveguide and horn calculator

Online rectangular waveguide calculator: TE10 and TE20 cutoff frequencies, guide wavelength, wave impedance, working range and the gain of a pyramidal horn.

Moxon antenna calculator

Online Moxon rectangle calculator using Cebik’s polynomials (MoxGen): dimensions A, B, C, D, E for any frequency and conductor thickness, plus gain and F/B.

Broadband HEX-beam calculator

Driven element and reflector lengths, the gap, and the turning radius.

Discone calculator

Online discone calculator: cone slant length, disc diameter, base diameter, the gap, and the upper end of the working range from the lowest frequency you give it.

Hairpin match calculator

Online hairpin (beta match) calculator: the reactance the shortened driven element needs, the inductance and length of the hairpin, and the impedance of the two-wire line.

Transmission lines and measurement

Coaxial line impedance calculator

Characteristic impedance, cutoff frequency and per-metre parameters from the conductor and shield diameters.

Balanced two-wire line calculator

The characteristic impedance of a two-wire line from the spacing and the conductor diameter.

Balanced line with square conductors calculator

The characteristic impedance for busbars and extrusions.

Coaxial line with a square shield calculator

Characteristic impedance and dimensions for a round conductor inside a square shield.

Stripline in a rectangular shield calculator

Characteristic impedance and strip width for a flat conductor inside a rectangular shield.

Stub matching calculator

Online single-stub matching calculator: the distance from the load, the length of a shorted and of an open stub, and both possible solutions.

SWR, Γ and return loss converter

Online converter: SWR ↔ reflection coefficient ↔ return loss ↔ reflected power, plus mismatch loss and load impedance.

Additional loss from SWR calculator

Online calculator of the extra feedline loss caused by mismatch: total loss, how many watts reach the antenna, and why the SWR at the input looks better than the real one.

Cable velocity factor calculator

Online measurement of a cable’s velocity factor from a resonance on a NanoVNA: vf, the permittivity of the insulation, capacitance per metre, and a comparison with the catalogue figure.

Cable fault distance calculator

Online cable fault location: the distance from the resonance spacing on a NanoVNA, from the reflection delay, or from the S11 phase, with the velocity factor applied.

Microstrip line calculator

Online microstrip calculator using Hammerstad’s formulas: characteristic impedance from the geometry, trace width for a wanted impedance, εeff and λg.

Coplanar waveguide calculator

Online coplanar waveguide calculator (CPW and CPWG): characteristic impedance from complete elliptic integrals, εeff and the wavelength in the line.

Coupled lines calculator

Online coupled lines calculator: even- and odd-mode impedances for a wanted coupling, the inverse problem, and the length of the coupled section.

Coax power handling calculator

Online estimate of how much power coaxial cable will take: the dielectric breakdown limit and the heating limit, corrected for SWR and temperature.

Coaxial cable loss calculator

Power lost in the cable and the connectors at different frequencies.

Transmission line length calculator

Quarter-wave and half-wave sections with the velocity factor applied.

Matching and baluns

L-network calculator

Online L-network matching calculator: component values for the low-pass and high-pass versions, the Q, the bandwidth and compensation of load reactance.

Pi-network calculator

Online pi-network output tank calculator: C1, L and C2 for a chosen Q, the bandwidth, harmonic suppression and the voltage across the capacitors.

T-network tuner calculator

Online T-network matching calculator: L1, C and L2, the virtual impedance, the bandwidth, and the efficiency as a function of coil Q.

Impedance equivalents calculator: series ↔ parallel

Everything for working with a NanoVNA.

Quarter-wave transformer calculator

Characteristic impedance, section length and matching bandwidth.

Wilkinson divider calculator

Branch impedance, section length, balancing resistors and the LC equivalent.

Filters and crystals

LC low-pass and high-pass filter calculator

Online LC low-pass and high-pass filter calculator using Butterworth or Chebyshev prototypes: component values, the nearest E12 and a table of stopband attenuation.

LC bandpass filter calculator

Online LC bandpass filter calculator: transforming a low-pass prototype into series and parallel tuned circuits, with a warning when the bandwidth gets too narrow.

Crystal ladder filter calculator

Online crystal ladder filter calculator: coupling capacitors, termination impedance, external Q and how closely the crystals must be matched.

Quartz crystal parameters calculator

Online crystal parameter calculator: Cm, Lm, Q and the parallel resonance from measured fs and fp or by the G3UUR method, plus the pulling range.

Diplexer calculator

Online constant-impedance diplexer calculator for a mixer: first- and third-order low-pass and high-pass branch values, with an explanation of why the unwanted branch must be terminated.

Notch filter calculator

Online notch filter calculator: notch depth as a function of coil Q, the width of the notch at various levels, and both the series and parallel arrangements.

Oscillators and synthesis

LC oscillator calculator: Colpitts, Clapp, Hartley

Online LC oscillator calculator: frequency, feedback ratio, the condition for oscillation, and how sensitive the frequency is to the active device’s capacitance.

PLL calculator: dividers and loop filter

Online PLL synthesiser calculator: divider ratios, the loop’s natural frequency and damping, in-band phase noise and the lock time.

DDS calculator: tuning word, images and spurs

Online direct digital synthesis calculator: the frequency tuning word, the resolution, the first image frequency, the sinc roll-off and the SFDR.

VXO calculator: pulling a crystal

Online VXO calculator: the tuning range of a crystal oscillator from load capacitance, the theoretical maximum, and how a series coil extends it.

Receive path

Cascade noise figure calculator

Online receive-chain noise figure calculator using Friis’s formula: the contribution of each stage separately, the noise temperature, and a comparison of where to put the preamplifier.

Receiver sensitivity and MDS calculator

Online receiver sensitivity calculator: the MDS noise floor from bandwidth and noise figure, conversion to microvolts, and a comparison with external band noise.

IP3, intermodulation and dynamic range calculator

Online IP3 calculator: intercept points from a two-tone measurement, the level of third-order products, the DR3 dynamic range and the effect of an attenuator.

S-meter calculator: S-points, dBm, microvolts

Online signal level converter: S-points ↔ dBm ↔ microvolts ↔ dBµV on the IARU scale, for HF and VHF.

Power and safety

ERP and EIRP calculator

Online ERP and EIRP calculator: dBi ↔ dBd conversion, losses in cable and connectors, and the effective area of the antenna.

Safe distance from an antenna calculator

Online RF exposure safe-distance calculator: the Ukrainian DSanPiN limits and ICNIRP, time averaging, and the far-field boundary.

mW to dBm converter

MW to dBm and back, with a reference table of typical levels.

Propagation and location

QTH locator calculator

Online Maidenhead QTH locator converter: coordinates ↔ locator up to 10 characters, the centre and bounds of the cell, and the eight neighbouring squares.

Great-circle bearing and distance calculator

Online calculator of bearing and distance between two locators or coordinates: short and long path, forward and reverse bearing.

Radio link budget calculator

Online link budget calculator: EIRP, free-space loss, the level at the receiver input and the margin above sensitivity.

Urban path loss calculator: Hata and COST-231

Online path loss calculator using the Okumura–Hata and COST-231 models: urban, suburban and open terrain, with a check on the range of validity.

Two-ray model and breakpoint calculator

Online two-ray propagation calculator: the breakpoint, the loss beyond it, the path difference between the rays, and a table of loss against distance.

MUF and hop length calculator

Online calculator of the maximum usable frequency from foF2: the secant factor, the working frequency, the number of hops and the longest single hop.

Satellite link parameters calculator

Online satellite calculator: orbital velocity, period, slant range, footprint radius and Doppler shift across the amateur bands.

Sunrise, sunset and grey line calculator

Online sunrise and sunset calculator from a locator or coordinates: times in UTC and local, the grey-line windows, solar declination and the equation of time.

Fresnel zone calculator

Online Fresnel zone calculator for the radius of the first Fresnel zone, for planning radio links and wireless networks.

Line-of-sight range calculator

Line-of-sight range between antennas with refraction taken into account.

Point-to-point radio link calculator

The maximum range of a Wi-Fi link from power, antenna gain and receiver sensitivity.

Coil calculations

Single-layer inductor calculator

Number of turns and inductance from Lundin's formula with Rosa's corrections.

Multilayer inductor calculator

Turns, layers, wire length and resistance by Maxwell's method.

Rectangular-former multilayer coil calculator

Turns and layers from Grover's formulas for straight segments.

PCB coil calculator

Number of turns, pitch and track width.

Flat spiral Tesla coil calculator

Turns, outer diameter and wire length by Maxwell's method.

Rectangular loop inductance calculator

Inductance of a single-turn loop from Grover's formula.

Triangular loop inductance calculator

Inductance of an isosceles loop of round wire.

Foil-wound coil calculator

Turns, diameter and foil length via the geometric mean distance.

LC resonance calculator

Frequency, inductance, capacitance and characteristic impedance in four modes.

Ferrite toroid coil calculator

Number of turns, the AL factor and the wire length.

Ferrite toroid permeability calculator

Μr and AL of an unknown ferrite from a measured inductance.

Ferrite rod coil calculator

Turns of a coil on a ferrite rod, allowing for its offset.

Amidon ferrite toroid calculator (FT series)

Turns from the catalogue AL, with a reference table of materials.

Amidon iron-powder toroid calculator (T series)

Turns from the catalogue AL, with tables of materials and the colour code.

Ferrite toroid at radio frequencies

Impedance, Q and self-capacitance from the Fair-Rite complex permeability data.

E-core ferrite coil calculator

Turns, effective parameters and saturation current to IEC 60205.

Binocular transformer calculator

Primary and secondary turns, inductance and reactance.

Common-mode choke calculator

Online common-mode choke calculator on a ferrite toroid: R, X and |Z| from the Fair-Rite complex permeability, for every HF band.

Inductor colour code calculator

The inductance value from the markings, including the military standard.

Inductive reactance calculator

X = 2πfL with careful unit conversion.

Conical Tesla coil calculator

Inductance computed numerically by Maxwell's method instead of Wheeler's formulas.

Wire-above-plane inductance calculator

The inductance and characteristic impedance of a length of line at UHF.

Helical resonator filter calculator

A two-section band-pass filter worked out from the passband to every dimension.

AWG to millimetres converter

Wire gauge to diameter, cross-section and resistance, and back.

Coil self-capacitance calculator

C₀ and inductance by regression over a series of resonances.

SMD and capacitor marking calculator

Code to value and back.

Air variable capacitor calculator

Online air variable capacitor calculator: capacitance from the plate geometry, breakdown voltage from the gap, and a reverse fit to a given capacitance and voltage.

Electronics and construction

PCB trace width calculator

Online trace width calculator to IPC-2221: outer and inner layers, cross-sectional area, trace resistance and voltage drop.

Heatsink calculator

Online heatsink thermal calculator: the thermal resistance needed, the junction temperature, the effect of thermal compound and airflow, and an area estimate.

Divider, LED and zener calculator

Online calculator for three basic circuits: the series resistor for an LED, a voltage divider with its load taken into account, and a zener shunt regulator.

555 timer calculator

Online NE555 timer calculator: frequency and duty cycle in astable mode, component values for a target frequency, and monostable mode.