“20km range” is the least useful number you’ll see printed on a radio box. It gets measured over open water, on a clear day, antenna pointed, nothing in the way. Real flights don’t look like that. Stand at the edge of a field with a ridge behind you and the gap between the box claim and the range you actually get comes down to three things: line of sight, antenna gain, and whatever sits between the two ends.
Quick answer: A quoted 20km is measured over open water on a clear day with the antenna pointed and nothing in the way. Real range comes down to three things: line of sight, antenna gain and whatever sits between you and the aircraft. An obstruction counts once it pokes into the first 60% of the Fresnel zone, so height is the single most effective lever. A higher-gain antenna only helps along its beam axis: the AT1400 suits a fixed corridor, the AT2458 an aircraft that orbits. A relay routes around terrain, a TR01 dual-band repeater carries distance on the same path, and dual-band 2.4GHz and 5.8GHz buys steadier behaviour when one band is congested. See the relay guide and the avionics guide.
| Problem | What actually helps | What does not |
|---|---|---|
| Terrain blocks the line | A relay placed on higher ground | More transmit power |
| A long straight corridor | AT1400 high-gain directional antenna | Higher gain off the beam axis |
| An aircraft that orbits | AT2458 mini directional antenna | A narrow beam you cannot track |
| Distance over open ground | TR01 dual-band repeater | A relay with nothing to route around |
| A congested band | Dual-band 2.4 and 5.8 GHz | Pushing one band harder |
| Flying low behind a ridge | Fly higher; the Fresnel zone closes | A bigger antenna on the ground |
So let’s break down what really limits a UAV data link, and then look at how antennas and relays push it past those limits.
Range is a claim about a straight line
Every quoted range assumes free-space propagation: two antennas, nothing between them, no multipath. Put one obstacle in the path and you’re out of that tidy case, and the usable range falls apart. A single tree line, a warehouse wall, the crest of a hill. Any one of those can take a link from kilometres down to hundreds of metres.
Here’s the practical rule. The path decides your range, not the radio. Before you compare two products on their range figure, model the path you’ll really fly.
Line of sight is not the horizon
Radio line of sight is a straight line between the antennas with the Fresnel zone clear. That zone is the football-shaped volume around the line, and an obstruction counts once it pokes into the first 60% of it. Fly low behind a small rise and you’re still blocked, even though both antennas can technically “see” each other’s position on a map.
That leaves you three things you can act on. Height beats power, because lifting the antenna clears the Fresnel zone. Skimming low over undulating ground cuts range hard. And your ground station antenna height matters as much as the aircraft’s, which is why a tripod wins over holding the controller at chest height.
Antenna gain and directivity
An antenna doesn’t create power. It shapes it. A high-gain directional antenna squeezes the available energy into a narrow beam, so range stretches along the beam axis and coverage shrinks off it. A low-gain omni stays roughly even in all directions and gives you less distance for the same power.
Fly a survey aircraft down a fixed corridor and a directional antenna like the AT1400 high-gain directional antenna is the right trade, because the beam points wherever the aircraft is. For an aircraft that orbits, the smaller AT2458 mini directional antenna is easier to keep on target. The pairing we see people get wrong is a high-gain beam on a mission that circles the operator. Now the beam sits on empty sky most of the flight.
Polarisation matters too. Get the orientation mismatched and you’ve given away several dB before anything else goes wrong. Keep both ends on the same orientation and that loss never shows up.
Relays and repeaters: extending past the obstacle
When you can’t see the aircraft from the ground, you carry the link through a second radio sitting in between. That’s a relay, and it works like a hilltop microwave hop: the relay has line of sight to both ends, even when those two ends can’t see each other at all.
The TR01 repeater is a dual-band 2.4GHz and 5.8GHz unit built for exactly this, and the GR02 relay receiver covers the receiving half of the chain. If it’s video you’re pushing, the relay case is walked through in full in the video transmission relay guide.
A relay costs you a hop of latency and a second site to power and position. That’s the price. But it’s the only way we know to fly behind a ridge and keep a stable video feed. On fixed installations, the video transmission boxes YL20 and YL50 let you build the chain with no controller at either end.
Frequency and dual-band behaviour
Lower frequencies push through and bend around obstacles better, but they carry less bandwidth. Higher frequencies carry more data and need a cleaner path. That’s the whole reason dual-band links exist: 2.4GHz for penetration and control margin, 5.8GHz for video bandwidth when the path is clean. The radio hops between them as conditions change, which holds up far better than either band on its own.
What that means when you’re picking a link in the first place is covered in telemetry radios for UAVs, and the controller half of the same decision sits in the Skydroid controller and video link guide.
A practical range checklist
Raise the ground antenna. A tripod and two metres of height usually buy you more than any amplifier will.
Point the beam. Fitted a directional antenna? Keep it on the aircraft, not on the operator.
Check the path. Fly the route on a terrain map first. Every obstruction you can predict is one you won’t find out about the hard way, in the air.
Separate the antennas. Park video and control antennas too close together and they eat into each other’s range.
Match polarisation. Both ends, same orientation.
Test before you commit. Fly the far corner of the mission on a calm day before you ever fly it loaded.
Frequently asked questions
Will a higher-gain antenna always give more range?
Only along the beam axis. A higher-gain antenna narrows the beam, so an aircraft that manoeuvres off-axis loses the link sooner rather than holding it longer, as the relay guide explains.
Does more transmit power fix a blocked link?
Rarely. Power helps at the margin. Obstruction is the loss that dominates, and no legal power level climbs over a hill.
Why does range drop when the aircraft descends?
Because the Fresnel zone closes down against the terrain. Height is the single most effective range lever you have.
Is a relay worth the latency?
If the mission needs video from behind an obstacle, yes. On a clean line-of-sight mission a relay just adds complexity and buys you nothing.
Should control and video share one antenna?
No. Keep them physically apart and on different bands where you can. Close together, they interfere with each other, which is the separation we describe in the avionics guide.
Tell us the route and the terrain and we will match the antenna, the relay and the radio combination that holds the link over it. The range sits on our Skydroid systems page, and the pillar guide is the UAV avionics guide.
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