Antenna Gain & Link Budget Calculator
Enter your transmit power, antenna gains, frequency, and path distance to get free-space path loss, EIRP, received signal level, and link margin. Works for ham radio, LoRa, IoT, and FPV links. Nothing uploaded.
Link Parameters
Link Budget
Learn more: RF link budgets and the Friis equation
What is link budget and why it matters
A link budget is an accounting of all gains and losses in a radio transmission path. It starts with the transmitter power, adds antenna gains, subtracts free-space path loss and cable losses, and compares the received signal level to the receiver sensitivity. The link margin (dB above sensitivity) determines how reliable the link will be in practice. Whether you are planning a LoRa sensor network, a ham radio repeater link, or a long-range FPV drone system, the question is the same: is there enough signal at the receiver?
Free-space path loss and the Friis equation
Free-space path loss is the signal attenuation between transmitter and receiver assuming no obstacles, reflections, or absorption. It increases with the square of distance and the square of frequency. The formula is FSPL (dB) = 20*log10(d_km) + 20*log10(f_MHz) + 32.44. Doubling the distance adds 6 dB of loss; doubling the frequency adds another 6 dB. The Friis equation (also called the Friis transmission formula) uses this to predict the signal level at the receiver given all gains and losses.
Link margin and reliability
Link margin is the received signal level minus the receiver sensitivity - how many dB above the minimum detectable signal you are. A link margin of 10 dB or more is considered reliable for most outdoor applications. 6 dB is the minimum acceptable for a clear line-of-sight link. Below 0 dB the link will not work. For links with obstructions or in challenging urban environments, aim for 15-20 dB margin.
FAQ
What is link budget in RF communications?
A link budget is an accounting of all gains and losses in a radio transmission path. It starts with the transmitter power, adds antenna gains, subtracts free-space path loss and cable losses, and compares the received signal level to the receiver sensitivity. The link margin (dB above sensitivity) determines how reliable the link will be in practice.
What is free-space path loss (FSPL)?
Free-space path loss is the signal attenuation between transmitter and receiver assuming no obstacles, reflections, or absorption. It increases with the square of distance and the square of frequency. The formula is FSPL (dB) = 20*log10(d_km) + 20*log10(f_MHz) + 32.44. Doubling the distance adds 6 dB of loss; doubling the frequency adds another 6 dB.
How much link margin do I need for a reliable link?
A link margin of 10 dB or more is considered reliable for most outdoor applications. 6 dB is the minimum acceptable for a clear line-of-sight link. Below 0 dB the link will not work. For links with obstructions or in challenging environments, aim for 15-20 dB margin.