Enter your radio and antenna parameters below to see received signal strength, link margin and maximum range — updated live as you type, right in your browser.
↓ Or read the full engineering guide below"Other losses" covers polarization mismatch, rain, foliage or any general safety allowance you want folded into the path.
A link budget is the complete accounting of every gain and every loss a radio signal passes through on its way from a transmitter to a receiver. It is the single calculation that tells you, before you ever power on a radio, whether a link will close at a given distance — and by how much margin.
In practice, the link budget answers one question: is the signal that arrives at the receiver stronger than the receiver's noise floor, by a comfortable margin? Every variable below — transmit power, cable loss, antenna gain, path loss, receiver sensitivity — exists to answer that question more precisely.
The power delivered to the transmitting antenna, boosted by that antenna's gain. Effective Isotropic Radiated Power (EIRP) is what a receiver actually "sees" leaving the transmit site in the direction it's pointed.
The unavoidable spreading of RF energy over distance, as the wavefront expands outward. This is the dominant loss term in almost every long-range link, and it grows with both distance and frequency.
A directional antenna doesn't create energy — it concentrates it into a narrower beam. Higher gain (dBi) means more signal on-axis, at the cost of a narrower beamwidth that demands better aim or tracking.
Sensitivity is the weakest signal a receiver can still decode reliably. Fade margin is the extra headroom, in dB, kept above that threshold to absorb multipath fading, weather and antenna misalignment.
Every professional link budget reduces to one balance sheet: what you transmit, minus what you lose, plus what your antennas add. Below is the exact form the calculator uses.
Where EIRP = PTX − LTX cable + GTX. Every term is in decibels, so the whole equation is simple addition and subtraction — no multiplication required.
This is the standard form for distance in kilometres and frequency in megahertz. Doubling the distance adds 6 dB of loss; doubling the frequency adds another 6 dB.
SRX is receiver sensitivity in dBm. A positive margin means the link closes; the size of that margin above your target fade margin tells you how reliable it will be.
| PTX | Transmit power delivered to the radio's RF output, in dBm. |
| LTX cable | Loss in the transmit coax, connectors and any filters, in dB. |
| GTX | Transmit antenna gain in the direction of the receiver, in dBi. |
| EIRP | Effective Isotropic Radiated Power — the equivalent power an isotropic antenna would need to match your directional signal, in dBm. |
| FSPL | Free-space path loss over the link distance at the operating frequency, in dB. |
| Lmisc | Additional losses: polarization mismatch, rain, foliage, or a general safety allowance, in dB. |
| GRX | Receive antenna gain, in dBi. |
| LRX cable | Loss in the receive coax and connectors, in dB. |
| PRX | Signal power actually delivered to the receiver input, in dBm. |
| SRX | Receiver sensitivity — the weakest signal it can decode reliably, in dBm. |
When the calculator shows a negative or marginal result, these are the levers that move the number the most — roughly in order of impact.
Gain is added on both ends of the link and costs nothing in transmit power or battery life. Moving from an 8 dBi patch to a 14 dBi EGLE-16C-1R, or up to the 19 dBi EGLE-64C-R, is usually the single biggest, cheapest improvement available.
Every extra dB lost in coax and connectors comes straight off your margin. Keep RF cable runs short, use low-loss coax, and minimize the number of connector pairs between the radio and the antenna feed point.
Free-space path loss assumes a clear line of sight. Terrain, foliage or structures that intrude into the first Fresnel zone add loss the equation doesn't capture — mount antennas as high as practical and check the path profile for long links.
Mismatched polarization (linear to circular, or opposite senses of circular) can cost 20 dB or more. Match RHCP to RHCP end-to-end, and if you need to share a frequency between two co-located links, pair an RHCP antenna with its LHCP counterpart for natural isolation instead.
Doubling transmit power buys only 3 dB, is limited by regulation and battery budget, and shortens flight time on airborne systems. It's a smaller and more expensive lever than gain, so use it last — and check local RF power regulations before increasing it.
A link that just barely closes on paper will drop out in the field. Design toward 10–20 dB of margin above sensitivity so multipath fading, temperature drift and imperfect aiming don't turn a calculated success into a real-world dropout.
Short, direct answers to the questions that come up most when planning an RF link.
If the calculator shows your link is marginal, the fastest fix is usually more antenna gain. Every EGLE antenna is designed and measured in Lithuania — tell us your distance, frequency and radio, and we'll help you pick the right model.