What is a good fade margin for a wireless link?

Aim for at least 10 dB of fade margin, and 20 dB or more for links that must stay up in rain, wind and seasonal foliage. Fade margin is how much stronger your received signal is than the receiver's minimum sensitivity — headroom for real-world conditions.

Do point-to-point wireless links need line of sight?

Yes — and not just a visible path but a clear Fresnel zone, the football-shaped space around the line of sight. Trees, buildings or terrain intruding into the Fresnel zone add loss beyond the free-space figure, so real links need margin and clearance, not just a sightline.

Wireless Link Budget Calculator

Q: What is free-space path loss?

Free-space path loss (FSPL) is how much a radio signal weakens travelling between two antennas with clear line of sight. It grows with distance and frequency: FSPL(dB) = 20·log10(distance) + 20·log10(frequency) + a constant. Higher frequencies lose more, which is why 5 GHz links need more gain than 900 MHz over the same distance.

For point-to-point wireless links — building to building, camera to base. Enter the radios, antennas and distance to get free-space path loss, received signal strength and fade margin, with a clear pass/fail.

Link parameters

Frequency

Distance

Distance units

TX power (dBm)

RX sensitivity (dBm)

From the radio datasheet at your target data rate (more negative = better).

TX antenna gain (dBi)

RX antenna gain (dBi)

Cable / connector losses (dB, both ends)

Link budget

—

fade margin → —

Free-space path loss—

EIRP (TX + antenna − loss)—

Received signal strength—

Receiver sensitivity—

Fresnel zone radius (60%, midpoint)—

Fade margin is received signal minus sensitivity — the headroom for rain, wind and foliage. Aim for ≥10 dB, ≥20 dB for critical links.

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Reading a link budget

A wireless link works if the signal arriving at the far radio is comfortably stronger than the weakest signal that radio can decode. The math adds up everything that helps — transmit power, both antenna gains — and subtracts everything that hurts — cable losses and, dominant over distance, free-space path loss. What's left is the received signal; how far it sits above the receiver's sensitivity is your fade margin, the headroom that keeps the link up when weather and seasons work against it.

Two real-world cautions the numbers alone won't tell you: you need a clear Fresnel zone (not just line of sight — obstructions near the beam still cost you), and regulators cap EIRP, so there's a legal ceiling on power-plus-antenna in each band. Design for margin, clearance and compliance together.

Frequently asked questions

What is free-space path loss?

Signal weakening between antennas over clear line of sight: FSPL(dB)=20·log₁₀(dist)+20·log₁₀(freq)+constant. Higher frequency and distance = more loss.

What's a good fade margin?

≥10 dB minimum; ≥20 dB for links that must survive rain, wind and foliage.

Do links need line of sight?

Yes, plus a clear Fresnel zone around it — obstructions near the beam add loss beyond free space.

Connecting two buildings without trenching? We do that.

AMT SYSTEMS LTD. designs and installs point-to-point wireless bridges linking cameras and networks between sites across Toronto & the GTA.

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