Link Budget Calculator
Compute received signal power and link margin from TX power, antenna gains, feeder losses and path loss, with a built-in free space path loss (FSPL) helper.
What a link budget is
A link budget totals every gain and loss between a transmitter and a receiver to predict how much signal actually arrives, and whether that is enough for the receiver to decode it reliably. It is the core calculation behind coverage planning, microwave backhaul design and any point-to-point RF link.
The link budget formula
Rx power(dBm) = TX power(dBm) - TX losses(dB) + TX antenna gain(dBi) - path loss(dB) + RX antenna gain(dBi) - RX losses(dB). Subtract the receiver sensitivity from that result to get the link margin: how much headroom the link has before it drops below a usable signal.
Free space path loss (FSPL)
FSPL models the unavoidable signal spreading loss over a clear line-of-sight path: FSPL(dB) = 20 × log10(distance km) + 20 × log10(frequency MHz) + 32.44. Doubling the distance or the frequency each add about 6 dB of loss. This calculator's FSPL mode fills in the path loss field automatically from distance and frequency.
Reading the link margin
A positive link margin means the predicted receive power clears the receiver sensitivity; the larger the margin, the more headroom against fading, rain, seasonal foliage or model error. A negative margin means the link is predicted to fail under the entered conditions. FSPL alone ignores terrain and clutter, so real deployments should budget extra margin on top of it.
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Frequently Asked Questions
What is a link budget?
A link budget adds up every gain and loss in a radio link, transmit power, antenna gains, cable losses and path loss, to predict the signal power arriving at the receiver, and how much margin that leaves above the receiver sensitivity.
What is the link budget formula?
Rx power(dBm) = TX power(dBm) - TX losses(dB) + TX antenna gain(dBi) - path loss(dB) + RX antenna gain(dBi) - RX losses(dB). Link margin(dB) = Rx power(dBm) - RX sensitivity(dBm).
What is free space path loss (FSPL)?
FSPL is the signal loss over a line-of-sight path with no obstructions, computed from distance and frequency: FSPL(dB) = 20 x log10(distance in km) + 20 x log10(frequency in MHz) + 32.44. Real-world paths usually have additional loss beyond FSPL from terrain, buildings and vegetation.
What link margin is considered safe?
A positive link margin means the received signal is above the receiver sensitivity threshold. Field engineers commonly target 10 to 20 dB of margin to absorb fading, rain attenuation and modeling uncertainty, the exact target depends on the system and reliability requirement.
Does FSPL account for obstructions?
No. FSPL only models loss in unobstructed free space. Real terrestrial links usually experience additional loss from terrain diffraction, foliage, buildings and multipath, so a real link budget should add a clutter or fade margin on top of FSPL.
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