Telescopic Masts for UAV Antennas: Why Raise the Antenna and How to Choose the Height

A telescopic mast lifts the antenna of a ground controller, signal booster or repeater to between 2 and 19 metres above the ground. For drone control at 2.4 and 5.8 GHz, the height of the ground antenna often matters more than transmitter power: signals at these frequencies bend poorly around obstacles, and an antenna held at head height loses the drone behind the first tree line. This article explains where the gain from height comes from, how a mast relates to countering electronic warfare (EW) and protecting the crew, and how to match mast height to a given position.

Why antenna height determines link range and stability

Line of sight

Drone control and video links operate in the 2.4 GHz, 5.8 GHz and 900 MHz bands, among others. The higher the frequency, the weaker the diffraction, meaning the wave's ability to bend around the edge of an obstacle. At 5.8 GHz, a hill, a building or a strip of trees between the antenna and the drone effectively breaks the link, and leaves and branches absorb additional signal. A stable link therefore needs line of sight between the antennas, and anything that provides it gives more than adding power.

Radio horizon

Even over perfectly flat terrain, line of sight is limited by the curvature of the Earth. The standard estimate, which accounts for normal atmospheric refraction, is:

d ≈ 4.12 × (√h₁ + √h₂), where d is in kilometres and h₁, h₂ are the antenna heights in metres.

Some examples for a ground antenna at 1.5 m (operator holding the controller) and at 12 m (on a mast):

For a reconnaissance drone flying at several hundred metres, the radio horizon is rarely the limit. For an FPV drone that flies its final approach a few metres above the ground, the height of the ground antenna becomes the dominant factor, because the drone's own contribution to the sum is close to zero. In practice the limit is set by terrain and vegetation rather than Earth curvature, and the same principle applies: an antenna raised above treetops and rooftops sees further.

Fresnel zone

A clear straight line between the antennas does not yet guarantee a clean signal. The radio wave occupies a volume shaped like an elongated ellipsoid around that line, called the first Fresnel zone. If ground, trees or buildings intrude into this zone, part of the energy is reflected and cancelled, even when the antennas can "see" each other. A reliable link needs at least 60% of the zone's radius to stay clear.

The radius at its widest point (mid-path) is calculated as:

r = 17.32 × √(d₁ × d₂ / (f × D)), where d₁, d₂ are the distances to each antenna in km, D is the total path length in km, f is the frequency in GHz, and r is in metres.

For a 10 km path this gives:

This shows why an antenna at head height underperforms its calculated range even in an open field: the lower part of the Fresnel zone lies in the ground and grass. An antenna raised to 8–12 m lifts most of the zone above the surface. Lower frequencies have a wider zone and depend even more on mounting height.

The mast, EW and crew safety

EW systems jam a drone's receiver by producing an interfering signal stronger than the useful one. The outcome is decided by the ratio of jamming power to control signal power at the receiver input. A mast does not make the signal "stronger" in terms of power, but it removes losses along the path: with no obstructions in the Fresnel zone and a margin of line of sight, a larger share of the radiated signal reaches the drone. The same transmitter with a raised antenna tolerates stronger jamming before the link drops. This is why masts are supplied together with signal boosters (Alientech, Avenger) and are also used to raise the antennas of EW systems themselves.

The mast's second function concerns crew survival. A transmitting antenna gives away the position: the enemy takes a direction-finding bearing on the source and can strike it. With the antenna on a mast and the operator working from cover a cable length away, a strike on the bearing lands on the antenna site. For the same reason masts are camouflaged: matte paint and camouflage covering reduce the structure's visibility from the air.

Beyond drone control, antenna masts are used for repeaters, Wi-Fi bridges, field radio stations, surveillance cameras and signals intelligence equipment. The requirement is the same in every case: put the antenna or sensor above obstacles and separate it from where people are.

Telescopic mast design

A mast consists of aluminium sections nested inside one another. Collapsed length is determined by the length of a single section, so even the 19-metre model measures 2.3 m in transport position. Each section is locked with a clamp once extended, and the quality of these clamps decides whether the mast sags under wind.

The base stands on a wide tripod. For shorter models this, together with ground stakes, is enough. From 10 m upward, wind load on the upper sections is high enough that without guy wires the mast sways and the antenna drifts off its bearing. Guy wires are attached in tiers: one tier holds the middle of the mast, and a second is added on tall models to keep the upper part from bending. For stability the wires are spaced evenly around the mast, at 120° when three wires are used.

Equipment is mounted on a removable mast head. The standard head fits most antennas and cameras, and a separate head is available for Alientech boosters. The removable design lets the antenna come down together with the head, without undoing the mount at height.

Accessories are selected to match the mast height: a transport cover, camouflage covering, powder coating in the required colour, guy wires and additional mast heads.

Mast range

The catalogue includes telescopic masts of 2, 4, 6, 8, 10, 12, 15, 17 and 19 m. Parameters for the models with verified data:

All models come with a standard removable mast head and sections with locking clamps.

Cable: what is lost between the mast and the controller

Raising the antenna means running coaxial cable up to it, and at microwave frequencies cable loss is significant. For reference, LMR-400 class cable (a low-loss replacement for RG-8) loses about 22 dB per 100 m at 2.5 GHz and about 35 dB per 100 m at 5.8 GHz, according to Times Microwave. Over 20 metres that is roughly 4.4 dB and 7 dB respectively. Every 3 dB halves the power, so at 5.8 GHz a 20-metre cable delivers less than a fifth of the signal to the antenna. Thinner cables lose more over the same length.

The takeaway for choosing height: a mast taller than needed brings no gain, only more metres of cable. The gain from lifting an antenna above an obstacle usually far outweighs the cable loss, but only if the obstacle is actually there. In an open field, the difference between 12 and 19 m is smaller than the loss over an extra 7 metres of cable at 5.8 GHz. Cable length should be measured from the controller to the mast head, with extra to reach cover, and when choosing a booster kit keep in mind that its cables come in fixed lengths. The Avenger Booster 2.4/5.8/5.2 GHz remote antenna kit, for example, includes two 20 m RG-8 cables with N-Type and QMA connectors.

The cable should be tied to the mast sections so that its weight does not hang on the antenna connector. LMR-400 weighs about 0.1 kg/m, so 20 m of cable weighs roughly 2 kg, and an unsecured run pulls the connector down and sways the top section.

Choosing the height for the task

2–6 m. Mobile positions, frequent relocation, open terrain without tall obstacles nearby. The 6-metre mast weighs 9 kg and collapses to 1.7 m, so one person can carry it and it fits in a car boot. The height is enough to lift the antenna above grass and scrub and clear the lower part of the Fresnel zone.

8–12 m. Positions near tree lines, in villages, or in broken terrain where the antenna has to clear treetops or rooftops. This is the most common range for FPV positions and remote boosters. At 10 and 12 m a tier of guy wires is added, so setup takes longer and needs space around the mast for the wires.

15–19 m. Long-term positions, repeaters, long-range links across difficult terrain. A weight of 20–24 kg and two tiers of guy wires on the 15-metre model make such a mast a fixed installation rather than something to move quickly. Cable calculation matters most here: at 5.8 GHz the loss up to the mast head becomes noticeable, and for this band a booster or repeater at the antenna is often better than a long feeder.

When siting a mast of any height, check for overhead power lines nearby: a metal mast that falls onto a line or touches it during setup is a lethal hazard. A mast in open ground is also the highest point around, so it should be lowered during thunderstorms.

Summary of selection parameters