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: 109

Antenna calculators

Flower Pot antenna calculator

A coaxial vertical dipole with a choke and no radials: leg lengths, choke cable length, resonance and velocity factors.

Ground Plane antenna calculator

Radiator and radial lengths for a quarter-wave vertical on any frequency, with the formulas and a live drawing of your dimensions.

J-pole antenna calculator

Radiator and matching-stub lengths for any VHF/UHF frequency, a half-wave vertical with no radials, with a live drawing of your dimensions.

Yagi antenna calculator (DL6WU)

Element lengths and spacing with boom correction and mounting type, plus a live drawing of your dimensions.

Kharchenko (BiQuad) antenna calculator

Two square loops in front of a reflector for Wi-Fi, 3G/4G and TV: element, reflector and spacing for your frequency.

Log-periodic antenna calculator (LPDA)

Element lengths and spacing, element count and gain for a wideband directional antenna, with a live drawing.

Dipole and Inverted-V calculator

Leg length corrected for wire thickness, feedpoint impedance versus height and the SWR to expect.

Magnetic loop calculator

Tuning capacitance, efficiency, Q, bandwidth, loop current and capacitor voltage, with a drawing.

Loaded vertical calculator

Loading coil inductance at the base, centre or 2/3 height, radiation resistance, efficiency and the effect of a capacitance hat.

Full-wave loop calculator

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

Receive loop calculator

Multi-turn loop inductance, tuning capacitance, effective height, induced EMF and the Q of the tuned circuit.

Capacitance hat calculator

Capacitance of a disc or spoked ring, how much smaller the loading coil gets and the rise in radiation resistance.

Radial system calculator

Ground loss resistance versus the number and length of radials, antenna efficiency and the gap to the reference 120 radials.

Coaxial trap calculator

Turns, inductance, capacitance, resonant frequency and the voltage across the trap, with a drawing of the coil.

EFHW and 49:1 transformer calculator

End-fed half-wave wire length, counterpoise, and a check that the 49:1 transformer has enough inductance on your ferrite core.

Random wire length calculator

Wire lengths for a 9:1 unun that avoid a multiple of a half wave on every band you select. A ready list for your band set.

Helical antenna calculator

Helix diameter and pitch, gain from Kraus, beamwidth, feedpoint impedance and axial ratio, with a drawing.

Parabolic dish calculator

Gain, beamwidth, focal length and depth, illumination angle and surface accuracy tolerance, with a drawing of your dish.

Patch antenna calculator

Patch width and length, effective permittivity, the 50 Ω feed point and bandwidth on FR-4 or Rogers, with a live drawing.

Waveguide and horn calculator

TE10 and TE20 cutoff, guide wavelength, wave impedance and working range, plus the gain of a pyramidal horn antenna.

Moxon antenna calculator

Dimensions A, B, C, D, E for any frequency and wire size, plus gain and F/B, with a live drawing.

Broadband HEX-beam calculator

Driven element and reflector lengths, the gap and turning radius, scaled to any band, with a drawing.

Discone calculator

Cone slant length, disc and base diameters, the gap and the upper frequency limit from the lowest frequency, with a drawing.

Hairpin match calculator

The reactance a shortened driven element needs, hairpin inductance and length, and the two-wire line impedance.

Transmission lines and measurement

Coaxial line impedance calculator

Characteristic impedance from the inner and shield diameters, cutoff frequency and per-metre parameters, with formulas.

Balanced two-wire line calculator

Characteristic impedance from wire diameter and spacing. What impedance your home-made ladder line will have.

Balanced line with square conductors calculator

Characteristic impedance for busbars, extrusions and rigid feeders.

Coaxial line with a square shield calculator

Characteristic impedance and dimensions of a round conductor inside a square shield, for rigid lines.

Stripline in a rectangular shield calculator

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

Stub matching calculator

Distance from the load and the length of a shorted or open stub, with both possible solutions and a drawing of the line.

SWR, Γ and return loss converter

VSWR ↔ reflection coefficient (S11) ↔ return loss in dB ↔ reflected power, plus mismatch loss and load impedance. What your SWR means.

Additional loss from SWR calculator

Extra feedline loss from mismatch, total loss, the watts that reach the antenna and why SWR at the radio looks better than at the antenna.

Cable velocity factor calculator

Measure a cable’s VF from a NanoVNA resonance: vf, insulation permittivity, capacitance per metre and a check against the datasheet.

Cable fault distance calculator

Find a cable break or short from NanoVNA resonance spacing, reflection delay or S11 phase, using the cable’s velocity factor.

Microstrip line calculator

Impedance from geometry, trace width for 50 Ω or any impedance, εeff and guided wavelength.

Coplanar waveguide calculator

Characteristic impedance from complete elliptic integrals, εeff and the guided wavelength, with a drawing.

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

How many watts a coaxial cable will take: the dielectric breakdown and heating limits, corrected for SWR and temperature.

Coaxial cable loss calculator

Attenuation in the cable and connectors at your frequency and length, and how many watts reach the antenna. Popular cable presets.

Transmission line length calculator

For transformers, stubs and phasing lines.

Matching and baluns

L-network calculator

Inductor and capacitor values for the low-pass and high-pass versions, Q, bandwidth and load reactance compensation.

Pi-network calculator

C1, L and C2 for a chosen Q, bandwidth, harmonic suppression and capacitor voltages, with the circuit.

T-network tuner calculator

L1, C and L2, the virtual impedance, bandwidth, and efficiency as a function of coil Q.

Impedance equivalents calculator: series ↔ parallel

Equivalents of a complex impedance plus Γ, SWR, return loss and equivalent L and C, for working with a NanoVNA.

Quarter-wave transformer calculator

The line impedance and section length to match two impedances, and the bandwidth over which the match holds.

Wilkinson divider calculator

Branch impedance, section length, balancing resistor and the lumped LC equivalent.

Filters and crystals

LC low-pass and high-pass filter calculator

Component values, nearest E12 values and stopband attenuation, with the circuit.

LC bandpass filter calculator

Series and parallel tuned-circuit values transformed from a low-pass prototype, with a warning when the bandwidth gets too narrow.

Crystal ladder filter calculator

Coupling capacitors, termination impedance, external Q and how closely the crystals must be matched, with the circuit.

Quartz crystal parameters calculator

Motional Cm, Lm, Q and parallel resonance from measured fs and fp or the G3UUR method, plus the pulling range.

Diplexer calculator

First- and third-order low-pass and high-pass branch values, and why the unwanted branch must be terminated.

Notch filter calculator

Notch depth as a function of coil Q, notch width at several levels, and both series and parallel circuits.

Oscillators and synthesis

LC oscillator calculator: Colpitts, Clapp, Hartley

Frequency, feedback ratio, the condition for oscillation and sensitivity to device capacitance.

PLL calculator: dividers and loop filter

Divider ratios, loop natural frequency and damping, in-band phase noise and lock time.

DDS calculator: tuning word, images and spurs

Frequency tuning word, resolution, first image frequency, sinc roll-off and SFDR.

VXO calculator: pulling a crystal

How far a crystal oscillator can be pulled with load capacitance, the theoretical maximum, and extending the range with a series coil.

Receive path

Cascade noise figure calculator

Each stage’s contribution, noise temperature, and where to put the preamplifier in your receive chain.

Receiver sensitivity and MDS calculator

MDS noise floor from bandwidth and noise figure, conversion to microvolts and a comparison with external band noise.

IP3, intermodulation and dynamic range calculator

Intercept point from a two-tone test, third-order product levels, the DR3 dynamic range and how an attenuator changes it.

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

S-units ↔ dBm ↔ microvolts ↔ dBµV on the IARU scale for HF and VHF. What S9 really means in microvolts.

Power and safety

ERP and EIRP calculator

EIRP and ERP calculator: the difference between them, dBi to dBd conversion, cable and connector losses, and the effective area of the antenna.

Safe distance from an antenna calculator

Safe distance from an antenna under ICNIRP and the Ukrainian DSanPiN limits, time averaging and the far-field boundary.

mW to dBm converter

Power in milliwatts to dBm and back, with a reference table of typical levels from receiver sensitivity to transmitter output.

Propagation and location

QTH locator calculator

Convert coordinates to a locator and back, up to 10 characters, with the cell’s centre, bounds and eight neighbouring squares.

Great-circle bearing and distance calculator

Great-circle distance between two Maidenhead locators or coordinates, short and long path, forward and reverse bearing.

Radio link budget calculator

EIRP, free-space path loss, received level and margin above receiver sensitivity: will the link work over your path?

Urban path loss calculator: Hata and COST-231

Urban, suburban and open terrain, with a check that your inputs are within the model’s range of validity.

Two-ray model and breakpoint calculator

Breakpoint distance, path loss beyond it, the path difference between the rays and a loss-versus-distance table.

MUF and hop length calculator

Maximum usable frequency from foF2, the secant factor, the working frequency, the number of hops and the longest single hop.

Satellite link parameters calculator

Orbital velocity and period, slant range, footprint radius and Doppler shift across the amateur bands.

Sunrise, sunset and grey line calculator

UTC and local times, grey-line windows, solar declination and the equation of time.

Fresnel zone calculator

The Fresnel zone is the ellipsoid around a line-of-sight path that has to stay clear of obstacles. Work out its radius for your frequency and distance: Wi-Fi, LTE, VHF.

Line-of-sight range calculator

Line-of-sight range between two antennas from their heights, with atmospheric refraction. How high your mast needs to be.

Point-to-point radio link calculator

Maximum range from transmit power, antenna gain and receiver sensitivity. Will your bridge reach?

Coil calculations

Single-layer inductor calculator

Turns for the inductance you need and the inductance of a given coil, from Lundin’s formula with Rosa’s corrections.

Multilayer inductor calculator

Turns, layers, wire length and resistance for a multilayer inductor, computed 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 for a printed spiral coil, with a drawing of the spiral.

Flat spiral Tesla coil calculator

Turns, outer diameter and wire length, with inductance by Maxwell’s method. For Tesla coils and flat inductors.

Rectangular loop inductance calculator

A single-turn rectangle of round wire from Grover’s formula, for loop antennas and tuned circuits.

Triangular loop inductance calculator

The inductance of an isosceles single-turn loop of round wire, for loop antennas and tuned circuits, with formulas.

Foil-wound coil calculator

Turns, diameter and foil length for a coil wound from strip or tape, using the geometric mean distance, with formulas and a drawing.

LC resonance calculator

Resonant frequency from L and C, or the L or C you need for a target frequency, plus characteristic impedance, from f = 1/2π√LC.

Ferrite toroid coil calculator

The number of turns from the AL factor for the inductance you need, and the length of wire to wind it, with formulas and a drawing.

Ferrite toroid permeability calculator

Μr and AL from the inductance you measured with a few turns. Find the material of an unmarked core.

Ferrite rod coil calculator

Coil turns on a ferrite rod, allowing for where the coil sits along the rod. For LW, MW and HF receivers.

Amidon ferrite toroid calculator (FT series)

Turns for the inductance you need from the catalogue AL value, with a reference table of ferrite materials.

Amidon iron-powder toroid calculator (T series)

Turns from the catalogue AL value, with tables of mixes and the colour code of the cores.

Ferrite toroid at radio frequencies

Impedance, Q and self-capacitance of a coil on a ferrite core from Fair-Rite complex permeability data.

E-core ferrite coil calculator

Turns, effective parameters and saturation current to IEC 60205, with a drawing of the core.

Binocular transformer calculator

Primary and secondary turns, inductance and reactance, with a drawing of the core.

Common-mode choke calculator

R, X and |Z| from Fair-Rite complex permeability on every HF band. How many turns you need.

Inductor colour code calculator

Read the inductance from the coloured bands (color code), including the military standard. Pick the colours, get the value.

Inductive reactance calculator

X = 2πfL for any coil at any frequency, with careful conversion between nH, µH, mH, kHz and MHz.

Conical Tesla coil calculator

Inductance computed numerically by Maxwell’s method instead of Wheeler’s approximations, accurate where those formulas drift.

Wire-above-plane inductance calculator

Inductance and characteristic impedance of a length of line at UHF, for printed and wire-built RF circuits.

Helical resonator filter calculator

A two-section bandpass filter worked out from the passband to every dimension of the shield and helix. For VHF and UHF.

AWG to millimetres converter

Wire gauge to diameter in millimetres, cross-section in mm² and resistance, and back from mm to AWG.

Coil resistance calculator

Winding resistance from turns and wire diameter: at DC with temperature correction and at radio frequency with the skin effect. Skin depth, Q and heating.

Coil self-capacitance calculator

Find C₀ and the true inductance by regression over a series of resonances measured with different capacitors.

SMD and capacitor marking calculator

Decode resistor markings (3-digit, 4-digit, R notation, EIA-96) and capacitor codes, both ways: code to value and value to code.

Air variable capacitor calculator

Capacitance from plate geometry, breakdown voltage from the gap, and a reverse fit for the capacitance and voltage you need.