Radio range estimator

Work through a link budget, from transmit power to receiver sensitivity, and see roughly how far the link can reach. Useful for comparing radios, bands, and antennas before you build anything.

Frequency

Band

Frequency

MHz

Transmitter

Transmit power

dBm

Antenna gain

dBi

Losses

Losses: matching network, cable, connectors, and the enclosure. A small antenna inside a product often radiates well below its datasheet gain; count that here or in the gain.

Receiver

Sensitivity

dBm

Antenna gain

dBi

Losses

Sensitivity from the radio’s datasheet, at the data rate and packet error rate you need.

Or estimate sensitivity from bandwidth and noise figure

Bandwidth

kHz

Noise figure

Required SNR

Sensitivity ≈ −174 dBm/Hz + 10·log₁₀(bandwidth in Hz) + noise figure + required SNR. Spread-spectrum schemes such as LoRa can work below the noise, with a negative required SNR.

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Path

Environment

Path-loss exponent

Fade margin

The exponent sets how fast the signal falls with distance: 2 in free space, higher with walls and clutter. Fade margin covers fading, people, and day-to-day variation.

Estimate

Estimated range

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Free space

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Clear line of sight, antennas well above the ground

Your environmentFree spaceSensitivity plus margin

How the estimate works

The link budget adds up what the signal gains and loses between the two radios. Transmit power, less transmit-side losses, plus antenna gain, is the equivalent isotropically radiated power (EIRP). Add the receive antenna gain, take away the receive-side losses, and compare with the receiver’s sensitivity plus a fade margin: what is left is the most path loss the link can tolerate.

Range comes from a path-loss model. Up to 1 m the signal follows free space. Beyond that it falls by 10 × exponent dB for every tenfold increase in distance. With an exponent of 2 this is the free-space (Friis) equation, where each doubling of distance costs 6 dB.

Real links vary widely around any model. Treat the result as a way to compare options, not a promise of range.
Outdoors, keep the first Fresnel zone mostly clear of the ground and obstacles. Antennas close to the ground lose range quickly, even with clear line of sight.
Transmit power and antenna gain are limited by the rules in each market and band. Check the limits before you count on them.
Both directions of the link need to close. Run the numbers each way if the two ends differ.

Test where the product will be used

Antennas detune near batteries, metal, displays, and people, and buildings differ. Measure range with the product in its enclosure, in the places it will be used, and keep the margin you planned for.

Choosing a radio for a product?

If you are choosing a radio for a product and want a second opinion, get in touch.

info@westlakesys.com How to get started

Based in southern Indiana. Working with clients anywhere.