Attenuation (RF)

Attenuation (RF) is the reduction of signal power as a radio wave travels from transmitter to receiver. It accumulates from several mechanisms: the natural spreading of energy over an expanding wavefront, absorption and reflection by obstacles such as walls, terrain, and vegetation, loss in feed cables and connectors, and weather effects such as rain fade. Because it is measured in decibels, attenuation is logarithmic: every 3 dB of loss halves the power, and every 10 dB cuts it to a tenth, so losses that look small on paper compound brutally along a real path.

Free-space path loss

The dominant component on a clear line-of-sight link is free-space path loss — the weakening caused purely by the wave spreading out as it propagates, with no obstacle involved at all. Power density falls with the square of distance, following an inverse-square law: doubling the range costs 6 dB before anything gets in the way. Free-space loss also rises with frequency, so higher-band links shed more signal over the same distance — one reason sub-GHz bands like those used by LoRa reach so much farther than Wi-Fi at the same power, and penetrate buildings and foliage better besides. On a well-built link this single term usually swamps cable and connector losses combined.

The other losses that eat your link

Beyond free-space spreading, every element between radio and sky takes a bite. Coaxial feedline loses signal per metre — cheap thin coax can quietly cost more dB than an extra kilometre of distance — and every connector and adapter adds a fraction of a dB. Obstructions in the path add much more: vegetation soaks up RF (wet leaves worse than dry), and terrain or buildings intruding into the path's Fresnel zone impose losses even when you can nominally "see" the far end. Attenuation is also a tool: deliberate attenuators protect receivers during bench testing, and understanding loss lets you diagnose a weak link by walking the signal chain element by element.

Managing attenuation off-grid

For sovereign mesh operators running Meshtastic nodes, attenuation is the adversary every deployment fights. You counter it with placement first: keeping the path clear, raising antennas above clutter, and shortening or upgrading feedlines. Antenna gain is the honest multiplier — it focuses power where the link needs it — whereas simply cranking transmit power hits regional legal caps quickly and does nothing for the receive direction. Understanding where each dB goes is what lets a few hundred milliwatts of LoRa cross a valley, and it is the same discipline a node runner applies to any infrastructure they own end to end: measure the losses, fix the biggest one, repeat.

Decibel arithmetic worth memorizing

Because attenuation compounds multiplicatively, decibels turn it into simple addition, and a few anchors make field estimates fast: 3 dB is half the power, 10 dB is one tenth, 20 dB is one hundredth. A link budget is just a ledger — transmit power, minus feedline and connector losses, plus antenna gains, minus path loss, must land above the receiver's sensitivity floor with margin to spare for rain and fading. Work an example on paper before climbing a ladder: if the numbers say the link closes with 2 dB of margin, weather will eat it; aim for a comfortable buffer. And when a previously solid link degrades, think like a repair tech — water in a connector, a corroded crimp, or new foliage are far more common culprits than a failing radio.

Attenuation is the central loss term in path planning. See link budget for how it is tallied against transmit power and receiver sensitivity, Fresnel zone for obstruction loss, and dBm for the units everything is counted in.