RADIOMETEO · IZ6CLV

Radio Lab Tools

RADIOMETEO · RF LAB

From frequency to results.

Radio lab tools for amateur radio: RF calculators for wavelength, power, SWR, coaxial cable loss, dipoles and LC circuits. Enter your own values and explore related technical guides.

6 calculatorsOn-device calculations · No simulated readings

RF calculators

Wavelength

Theoretical free-space lengths from frequency.

Enter values and select Calculate.

Formula: λ (m) = 299.792458 / f (MHz). Actual antenna dimensions depend on design and surroundings.

Power and dBm

Convert power in watts and level in dBm.

Enter values and select Calculate.

dBm = 10 log10(P in mW). A theoretical conversion, not an instrument reading.

SWR from power

Estimate SWR from forward and reflected power.

Enter values and select Calculate.

SWR = (1 + √(Pr/Pf)) / (1 − √(Pr/Pf)). Requires reliable measurements; not a substitute for an instrument.

Cable attenuation

Calculate loss using your cable’s specified attenuation.

Enter values and select Calculate.

Loss (dB) = dB/100 m × length (m) / 100. Use the manufacturer’s specification at your frequency; connectors excluded.

Antennas and circuits

Half-wave dipole

Estimate a starting wire length for a single-band half-wave dipole.

Enter values and select Calculate.

Starting estimate for an HF wire dipole: 468 / f (MHz) in feet, converted to metres. Leave trimming margin and tune with an analyzer: height, wire and surroundings affect resonance.

LC resonance

Calculate ideal resonant frequency from an inductor and a capacitor.

Enter values and select Calculate.

f = 1/(2π√(L·C)). Ideal model: resistance, stray capacitance and component tolerances affect real circuits.

Explore all radio lab tools

Each lab page has calculators and guides dedicated to its topic.

SDR LabSDR receivers, setup and checks.Open page → Grid Locator & DistanceMaidenhead locators and distances between stations.Open page → QRM TroubleshootingIdentify interference and radio noise.Open page → Antennas & MeasurementsAntenna projects and test instruments.Open page → CAT/PTT ConfigurationRadio control, serial ports, PTT and troubleshooting.Open page → WEFAX ReceptionFrequencies, stations and reception of weather charts by radio.Open page → WebSDR ReceiversListen from your browser and NCDXF beacons on air now.Open page →

How to use the radio lab tools

Units and decimals

Enter the frequency in MHz (7.1 for 40 m, 145.5 for 2 m). Both comma and point work; results are rounded for reading but the calculation uses all digits.

From calculation to measurement

The calculators give theoretical starting values: a calculated dipole should be cut a little longer and trimmed with an antenna analyzer, because height, wire and nearby objects shift the resonance.

SWR and reflected power

An SWR of 1.5 reflects about 4% of the power, an SWR of 2 about 11%: with a short, good cable the real loss is small. What matters more is that the transmitter works within the limits set by its manufacturer.

Cable matters more up high

Attenuation grows with frequency: the same cable that loses little on HF can dissipate much of the power on VHF and UHF. Always use the manufacturer’s figure at your operating frequency.

dBm and decibels

0 dBm is 1 mW, 30 dBm is 1 W, 50 dBm is 100 W. Every 3 dB the power doubles or halves, every 10 dB it is multiplied or divided by ten.

Theoretical indicative values: always check measurements, equipment ratings and actual operating conditions.

Physical constant source: NIST/CODATA — speed of light in vacuum (c = 299 792 458 m/s).

ARRL — dipole dimensions · Analog Devices — LC resonance