Antenna placement

A LoRa radio is a few centimetres of circuit board. Where its antenna sits decides how many neighbours it reaches far more than which board you bought.

Line of sight comes first

At 868 MHz, radio waves travel in straight lines for practical purposes. Hills, buildings and dense trees block or weaken the signal. A node that can "see" another across open ground or rooftops will work; one behind a terrace of houses may not. We have no sourced range figures for urban or suburban UK use, so we do not give any: range depends heavily on line of sight. Meshtastic's antenna testing guide offers one data point: a tuned quarter-wave stubby antenna (under 10 cm) "should have a real-world range of a couple of km without significant obstacles". The condition at the end matters.

Use Meshtastic's Range Test module to measure instead of guessing, and the Site Planner (linked from Meshtastic's software page) to predict.

The Fresnel zone

Radio energy does not travel along a pencil-thin line. It occupies an ellipsoid ("football shape") between the two antennas. Meshtastic's guide notes this zone must be kept clear of obstructions. The radius of the first Fresnel zone at distance d1 from one end and d2 from the other is:

r = sqrt( λ × d1 × d2 / (d1 + d2) )

where λ is the wavelength (c divided by frequency). At the midpoint, d1 = d2 = D/2, so r = 0.5 × sqrt(λ × D).

For 868 MHz, λ = 299,792,458 / 868,000,000 = 0.345 m (a quarter wave is about 8.6 cm). Worked example for a link of length D:

A common engineering rule is to keep at least 60% of the first zone clear. Notice what this implies: a 2 km link needs roughly 8 m of clearance around the straight line at the midpoint. A node at window height on a ground-floor street will almost never achieve that. A node high on a roof, or a repeater on a hill, can.

Why height beats power

Free-space path loss in dB is 20 log10(d in km) + 20 log10(f in MHz) + 32.44. At 868 MHz that is about 91.2 dB at 1 km, 97.2 dB at 2 km, 105.2 dB at 5 km and 111.2 dB at 10 km. Every doubling of distance costs 6 dB, whereas doubling transmit power buys only 3 dB. These are the ideal, unobstructed numbers. Obstructions in the Fresnel zone add loss on top.

In the UK you also cannot raise power much (see below). So the two levers you control are antenna height and a clear path. In practice:

Glass and building materials

We have no direct measurement of low-E (low-emissivity) glass at 868 MHz. What we found:

• Low-E coatings are thin metallic layers. A study of low-E double glazing found it attenuates by at least 20 dB more than standard glazing, but that was at 8 to 12.5 GHz, not 868 MHz. Other work cited 7 to 9 dB (2.4 GHz) and 14 to 17 dB (5 GHz) differences in shielding.
• Do not extrapolate those figures to 868 MHz. The safe reading is qualitative: metallised coatings attenuate more than clear glass, so a window with such glazing may cost you signal.

We found no sourced attenuation figures for brick, concrete or foil-backed insulation at 868 MHz, so we give none. The practical test is to move the node and check with the Range Test module.

Stock antennas

Boards usually ship with a small stub or spring antenna. Their quality varies, and we have no sourced figure for how much a replacement helps. Meshtastic's guide recommends aiming for a VSWR (standing wave ratio) below 2 at the tuning frequency, and its antenna index lists community-favourite antennas and SWR test reports. Two cautions:

1. Buy an antenna for your band. At least one antenna listed in Meshtastic's index (the Alfa AOA-915-5ACM) is a 915 MHz part, which is the wrong band for the UK.
2. Keep antennas vertical. A node lying flat or antennas at mixed angles can cost signal, because LoRa antennas are normally vertically polarised.

Cable loss

If you place the antenna away from the radio, the cable between them attenuates the signal in both directions. Loss in dB scales with length, thinner coax loses more, and every 3 dB of loss halves the power. Keep the run short and use low-loss cable; mounting the radio close to the antenna and running power or Ethernet instead is often better than a long RF cable.

The UK power limit: e.r.p. includes antenna gain

Under Ofcom IR 2030 (v1.16, published 7 April 2026), the 869.40 to 869.65 MHz slot used by Meshtastic's EU_868 setting allows 500 mW e.r.p. with spectrum-access techniques per EN 300 220 (such as listen before talk) or, alternatively, a duty cycle of 10% or less. 500 mW e.r.p. is about 27 dBm e.r.p., or about 29.1 dBm e.i.r.p. The e.r.p. is measured relative to a half-wave dipole, and it includes antenna gain. Antenna gain quoted in dBi converts to dBd by subtracting 2.15 dB.

So the legal figure is: radio output, minus cable loss, plus antenna gain in dBd.

Cable loss in the table is an assumption for illustration. If your radio can reach 28 dBm, set the transmit power in the app so that radio output minus loss plus gain stays at or below 27 dBm e.r.p. That limit is our reading of IR 2030, not legal advice, and Ofcom can issue newer versions of the document.

Checklist

1. Fit the antenna before power.
2. Match antenna band (868 MHz in the UK) to your board.
3. Get the antenna as high and as clear of obstacles as is safe.
4. Keep any coax short; note its loss.
5. Calculate e.r.p. if you use a high-gain antenna or a 28 dBm radio.
6. Test with Range Test and adjust.

Next: power, hardware buyer's guide, find a local mesh.