What is a link budget?

A link budget is the sum of all gains and losses between a transmitter and receiver. It starts with transmit power, adds antenna gains, subtracts path loss, and compares the result against receiver sensitivity. A positive link margin means the signal is strong enough to be decoded; a negative margin means the link drops out.

What is the free-space path loss formula?

FSPL in dB equals 20·log10(d) + 20·log10(f) + 32.45, where d is distance in kilometres and f is frequency in MHz. It models signal weakening in open air with line of sight. Real FPV flights have extra losses from obstacles, the ground, and antenna polarisation mismatch, so achievable range is always less than the free-space figure.

Why does higher frequency reduce range?

Free-space path loss rises with frequency, so a 5800 MHz (5.8 GHz) link loses more signal over the same distance than a 1300 MHz link. That is why long-range FPV often uses lower bands. Higher frequencies allow smaller antennas and more channels, which is why 5.8 GHz dominates racing despite the shorter range.

What receiver sensitivity should I use?

Analog FPV receivers are typically around -85 to -90 dBm for a usable picture. Digital systems vary; check your goggle or VRX datasheet. A more negative number means a more sensitive receiver and longer range. The tool uses sensitivity as the threshold at which the link margin hits zero.

Does this account for obstacles and interference?

No. This is a free-space, line-of-sight estimate that assumes a clear path and perfectly matched antennas. Trees, buildings, ground reflection, polarisation mismatch, and 2.4 GHz Wi-Fi noise all reduce real range. Treat the result as an optimistic upper bound and apply a safety margin of 6-10 dB for practical flying.

FPV Drone Link Budget Calculator

The FPV Drone Link Budget Calculator estimates the theoretical maximum range of a first-person-view video link using the standard radio link-budget equation. It helps FPV pilots understand how transmitter power, antenna gain, frequency, and receiver sensitivity combine to set the range limit — and why a “1000 mW” VTX does not simply quadruple range over a 250 mW one.

How it works

Every radio link obeys the same accounting. The received signal level in dBm is:

P_rx = P_tx(dBm) + G_tx(dBi) + G_rx(dBi) − FSPL(dB)

where the free-space path loss at distance d (km) and frequency f (MHz) is:

FSPL = 20·log10(d) + 20·log10(f) + 32.45

Transmitter power in milliwatts is converted to dBm with P_dBm = 10·log10(P_mW). The link margin is the received power minus the receiver sensitivity. As long as the margin is positive, the picture holds; when it reaches zero the link is at its theoretical edge.

The tool solves the equation for distance at zero margin to give the maximum range:

FSPL_max = P_tx + G_tx + G_rx − sensitivity
d_max(km) = 10^((FSPL_max − 20·log10(f) − 32.45) / 20)

Worked example and tips

A 600 mW VTX (≈ 27.8 dBm) with a 2 dBi transmit antenna and a 10 dBi patch receive antenna at 5800 MHz, into a -90 dBm receiver:

Effective budget = 27.8 + 2 + 10 − (−90) = 129.8 dB of allowable path loss.
Solving FSPL for distance gives a free-space range of several kilometres — far beyond what trees and ground reflections actually allow.

Practical tips:

Doubling power adds only 3 dB, which extends free-space range by about 40%. Antenna gain and clean line of sight matter far more than raw watts.
A high-gain patch antenna on the receiver is the cheapest range upgrade because gain helps without raising your transmit power or breaking local power limits.
Always check the legal power limit for your band and country. This tool does not enforce regulatory caps.
Apply a 6-10 dB safety margin below the calculated maximum for reliable flying — the free-space figure ignores obstacles, multipath, and polarisation loss.