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RF Link Budget Calculator

Calculate the complete RF path from transmitter output to receiver input, including feed-system losses, antenna gains, free-space path loss, receiver sensitivity and required fade margin. Reverse mode estimates the maximum ideal free-space distance.

Link inputs

Carrier or centre frequency.
Choose the broad area surrounding the terminals. The automatic clutter correction uses antenna height and frequency where the ITU-R P.2108 height-gain model applies.
Automatic vegetation loss uses an ITU-R P.833 mixed-forest reference model. Low and moderate vegetation use transparent planning-density factors rather than pretending to be separate ITU vegetation classes.
Automatic building entry uses the median ITU-R P.2109 model where applicable. Intervening buildings along the path are highly site-specific; use Custom for a measured or engineered obstruction allowance.
Optional extra allowance for known local obstructions or conditions not captured by the selections above.
Optional non-environmental allowance for filters, polarisation mismatch, implementation loss and similar system effects. Environmental loss is calculated separately above.
The available presets change with frequency. Automatic mode chooses a sensible starting reference, but you can override it.
Minimum received signal level required by the receiver.
Used for µV ↔ dBm conversion. Broadcast FM tuner specifications commonly use 75 Ω; communications receivers commonly use 50 Ω.
In reverse mode, this becomes the minimum margin the calculated maximum distance must still provide.
End-to-end RF link budgetLive calculation

How the link budget works

The RF link budget simply adds gains and subtracts losses in decibels as the signal travels from the transmitter to the receiver.

EIRP = PTX − LTX + GTX
PRX = EIRP − FSPL − Lother + GRX − LRX
Link margin = PRX − Receiver sensitivity

Worked example

Enter values above to see the complete link budget worked through here.

Maximum-distance mode

In reverse mode, the calculator first determines the maximum allowable free-space path loss that still leaves the selected required margin, then solves the FSPL formula for distance.

Environment model

The Environment section adds losses separately from free-space path loss. Broad terminal clutter uses the ITU-R P.2108 height-gain correction for 30 MHz to 3 GHz, including the standard open/rural, suburban, urban/trees/forest and dense-urban categories. If the antennas are above the representative clutter height, the terminal correction falls to zero.

Vegetation uses the ITU-R P.833 mixed-forest excess-loss relationship. The dense-woodland option uses the mixed-forest reference directly; the low and moderate vegetation selections deliberately apply smaller planning-density factors and are labelled as estimates rather than formal ITU vegetation classes.

If a terminal is inside a building, the traditional and thermally-efficient options use the median ITU-R P.2109 building-entry model. The thermally-efficient class is intended for structures with features such as metallised glazing, foil-backed panels, thick reinforced concrete or metal cladding. A custom building loss remains available for measured or site-specific situations.

Receiver sensitivity presets

The receiver presets are planning references derived from published equipment specifications, not universal standards. Sensitivity depends on receiver type, modulation, bandwidth and the measurement criterion such as 10 dB S/N, 12 dB SINAD or digital BER. The calculator therefore suggests receiver families from frequency but always allows a custom value.

µV and dBm sensitivity

The calculator can express receiver sensitivity as either dBm or microvolts. Conversion assumes RMS voltage across the selected resistive reference impedance. Some equipment manuals use different voltage conventions such as source EMF, so use the manufacturer's own specification convention when an exact equipment comparison is required.

About fade margin

A positive margin simply means the predicted signal is above the receiver sensitivity. Real links normally need additional margin to survive fading, obstruction, weather, antenna misalignment and other variability.

Free-space limitation

The distance result is an ideal free-space result, not a terrain-coverage prediction. Add realistic extra losses where appropriate, and remember that line-of-sight, Fresnel clearance, antenna height and clutter can dominate real-world performance.