KevsRobots Learning Platform
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By Kevin McAleer, 5 Minutes
Your antenna matters more than your transmit power. A £5 antenna change can do more for your range than any setting in the firmware. This lesson covers what to buy, what not to do, and what the rules are in the UK.
Never power on a LoRa board without an antenna connected.
Why this matters: With no antenna, the RF energy the SX1262 generates has nowhere to go. It reflects straight back into the power amplifier. Do this repeatedly and you will damage the radio - permanently, and in a way that looks exactly like “my board mysteriously has terrible range now”.
Fit the antenna before you plug in the USB cable. Every time. It is a two second habit that saves £15 boards.
Tuned for the band. An antenna cut for 433MHz or 2.4GHz will radiate badly at 868MHz. Buy one explicitly sold as 868MHz or 863-870MHz.
Vertical. LoRa nodes almost universally use vertical polarisation. If your repeater’s antenna is vertical and your client’s is lying flat on a desk, you throw away up to 20dB. That is most of your range, gone, for free.
Gain, honestly stated. A cheap “stubby” is typically 1-2dBi. A half-wave whip is around 2-3dBi. A collinear on a mast might be 5-6dBi. Higher gain squashes the radiation pattern flatter - which is ideal for a rooftop repeater covering a town, and bad for a handheld you carry up a hill.
Height beats everything. Seriously. Getting an antenna 5 metres higher will usually beat any upgrade you can buy, because LoRa at these ranges is dominated by line of sight and Fresnel zone clearance.
If you have limited budget, spend it in this order:
If you mount the antenna on a pole and run cable to the board, remember that thin coax is lossy. Cheap RG174 loses roughly 1dB per metre at 868MHz. Five metres of it throws away over half your transmit power and half your receive sensitivity.
Better plan: put the whole board in a small weatherproof box right at the antenna, and run the USB power up the pole instead. Power over a long cable is much more forgiving than RF over a long cable.
The 868MHz band is a licence-exempt Short Range Device band. You do not need an amateur radio licence, but you do have to stay inside the rules, which Ofcom publishes in Interface Requirement IR 2030.
The sub-band MeshCore uses in the UK and EU is 869.4 - 869.65MHz, and in that slice you are allowed:
How does that compare to your board? The Heltec V3 puts out around +21dBm - Heltec quote 21 ±1dBm - which is roughly 125 to 160mW. With a typical 2-3dBi antenna your ERP lands comfortably under the 500mW ceiling, so a stock board on stock settings is fine.
The duty cycle is the one to respect. It is not usually a problem for text messaging, but it is exactly why the community keeps settings narrow and fast - and why a badly configured node that adverts every few minutes is genuinely antisocial.
You may see MeshCore nodes on 433MHz. In the UK, 433MHz is a licence-exempt SRD band too, but with a much lower power allowance (typically 10mW ERP) and it shares space with car key fobs and weather stations. Stick to 868MHz unless you know exactly why you are not.
Not legal advice
Rules change and this is a summary, not a substitute for the actual document. If you are building anything beyond a hobby node - especially anything on a mast or with an amplifier - read the current version of Ofcom IR 2030 yourself.
Problem: My range is terrible even though both nodes are outside.
Solution: Check antenna polarisation and get at least one node higher.
Why: Mismatched polarisation and obstructed Fresnel zones cost far more than any firmware setting.
Problem: I powered the board up without an antenna once - is it dead?
Solution: Probably not, if it was only briefly and it had not transmitted. Test the range against a known good board.
Why: Damage is cumulative and comes from transmitting into an open circuit. Booting and immediately powering down is usually survivable - just do not make a habit of it.
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