Tools

Terrestrial radio link budget calculator

For links between terrestrial stations: estimate the received signal, signal‑to‑noise ratio, link margin and range of a point‑to‑point or point‑to‑area link. The notes below explain each step; enter your own values in the left‑hand panel and the results on the right update immediately.

How the calculation works

The calculation follows the signal from the transmitter to the receiver, adding gains and subtracting losses in decibels, then compares the received signal with the receiver noise.

EIRP is the transmitter power less filter and feeder losses, plus the transmit antenna gain.

Free‑space loss is 20·log(4πd/λ). It rises with the square of frequency and of distance.

Log‑distance model: free‑space loss is used up to the reference distance d₀, and the loss then increases by 10·n dB per decade of distance. Typical values of n are 2 for line of sight, 3 to 4 in suburban and urban areas, and more within buildings.

Two‑ray model: over flat ground the direct and ground‑reflected waves begin to cancel beyond the breakpoint distance d_b = 4·h_t·h_r/λ. Free‑space loss is used up to d_b, and n (classically 4) beyond it.

Fade margin: with log‑normal shadowing of standard deviation σ, the margin needed for reliability R is z·σ, where z is the standard normal value exceeded with probability 1 − R (1.645 for 95 %, 2.326 for 99 %).

Link margin is the signal‑to‑noise ratio at the chosen reliability, less the ratio the modulation needs.

Inputs

Enter or change these values

Transmitter

Transmitter power Filter and combiner loss dB Transmit antenna gain dBi Feeder loss dB

Path

Frequency MHz Path length km Path‑loss model Path‑loss exponent beyond the reference n Reference distance m Transmit antenna height m Receive antenna height m

Receiver

Receive antenna gain dBi Cable loss dB Filter / diplexer loss dB Receiver bandwidth kHz Receiver noise figure dB Required signal‑to‑noise ratio dB

Fading

Compute the margin from reliability Specify the margin

Shadowing standard deviation σ dB Required reliability % Fade margin dB

Results

Calculated from the inputs

–Link margin

–Range for 0 dB link margin

Transmitter power
Net transmitter power
EIRP
Free‑space path loss
Path loss used

Net receive antenna gain
Median signal at receiver input
Fade margin
Reliability (time / locations)
Signal exceeded at that reliability
Thermal noise, kTB
Receiver noise floor (kTB + NF)
Signal‑to‑noise ratio
Required signal‑to‑noise ratio
Link margin

Terrestrial links only. Assumes log‑normal shadowing, a noise temperature of 290 K (−174 dBm/Hz), and no co‑channel interference. The results are estimates for planning; a real link also depends on terrain, clutter, antenna patterns and installation. Ask about a detailed study.