What Is a Link Budget?

A radio-frequency (RF) link budget tallies gains and losses from transmitter to receiver in a wireless communication system. Engineers use it to estimate the power level arriving at the receiver’s input. If the received power falls below the minimum sensitivity of the equipment, the link becomes unreliable or fails entirely. By accounting for variables such as antenna gains, free-space path loss, and cable attenuation, you can design a link that meets performance goals whether it involves satellite relays, terrestrial microwave towers, or everyday Wi‑Fi networks.

Conceptually, a link budget represents a simplified version of the Friis transmission equation, which expresses received power as:

In this equation $\mathrm{P\_r}$ is the received power in dBm, $\mathrm{P\_t}$ is the transmit power in dBm, $\mathrm{G\_t}$ and $\mathrm{G\_r}$ are the antenna gains in dBi, and $L$ represents total losses in dB. Losses include free-space path loss, connector losses, atmospheric absorption, and any obstacles in the signal path. Because the units are logarithmic, adding gains and subtracting losses determines the link margin.

How to Use This Calculator

Enter your transmitter power, transmit and receive antenna gains, and the cumulative loss figure for the link. If you know the free-space path loss separately from other losses, you can sum them before input. After pressing Calculate, the script adds the gains to the transmit power and subtracts the loss to display the expected received power in dBm.

The result offers an instant check of whether the link meets a target threshold. For example, many Wi‑Fi devices require around –90 dBm for basic connectivity. If the calculator shows a received power above this threshold with some margin, your link is likely feasible. If the value is much lower, you may need higher gain antennas, increased transmit power, or shorter distances.

Interpreting RF Numbers

RF engineers often express power on a logarithmic scale using decibels referenced to one milliwatt (dBm). A 3 dB increase represents roughly double the power, while a 10 dB change corresponds to a tenfold difference. Gains from directional antennas, low-loss cables, or amplifier stages add to the link budget, whereas distance, obstructions, and atmospheric effects subtract from it. The key is ensuring that after all gains and losses are considered, sufficient signal remains to overcome the receiver’s noise floor.

The table below lists example components of a typical short-range link:

Element	Value (dB)
Transmit Power	20 dBm
Tx Antenna Gain	5 dBi
Free-Space Path Loss	80 dB
Rx Antenna Gain	5 dBi
Cable + Misc Losses	2 dB
Received Power	−52 dBm

From this budget, you can see that with modest antennas and only 20 dBm of transmit power, the received signal remains far above –90 dBm. Even after accounting for small cable losses, the link has roughly 38 dB of margin. Longer distances or higher frequency bands, however, dramatically increase path loss, necessitating directional antennas or higher transmit power.

Factors Affecting Path Loss

Free-space path loss grows with both distance and frequency. The Friis equation states that path loss in dB is $L=20\mathrm{log\_\{10\}}(d)+20\mathrm{log\_\{10\}}(f)+32.44$, where $d$ is distance in kilometers and $f$ is frequency in megahertz. Other factors such as rain fade, multipath reflections, and foliage absorption further attenuate the signal. These phenomena can be difficult to model precisely, so engineers often include a fade margin—an extra buffer in the link budget to ensure reliability.

Example Calculation

Imagine you are designing a 5 GHz point-to-point link with 23 dBm of transmitter power, 18 dBi directional antennas at both ends, and a free-space path loss of 110 dB at your chosen distance. If miscellaneous losses add another 2 dB, the received power computes as follows:

dBm

That equals –53 dBm—likely strong enough for a stable high-throughput link. If the result were closer to the receiver’s minimum sensitivity, you might shorten the distance or use larger antennas.

Planning for Reliability

A good RF design leaves margin above the sensitivity threshold for expected fading and interference. Urban environments, in particular, suffer from multipath reflections and competing signals. Rural microwave links contend with terrain blockage and weather-related attenuation. By experimenting with values in this calculator, you can explore how much margin remains if the path loss increases or the antenna gains change.

For advanced analysis, you may also consider the signal-to-noise ratio (SNR). Given a receiver noise floor, the SNR equals received power minus the noise level. Many communication protocols require a specific SNR for reliable throughput. Although this calculator focuses on raw received power, you can easily extend the computation with a simple MathML expression for SNR: $\mathrm{SNR}=\mathrm{P\_r}-N$, where $N$ is the noise floor in dBm.

Conclusion

Designing a wireless link involves balancing transmit power, antenna gain, and losses over the path. This RF Link Budget Calculator offers a quick way to estimate received power using straightforward addition and subtraction. Experiment with different scenarios—from short-range Wi‑Fi to long-distance microwave relays—and examine how each variable affects the bottom line. With a solid understanding of link budgets, you can ensure your communications remain clear and reliable in a variety of challenging environments.