Ground-station links
How to choose a UAV telemetry radio: data rate, range and ground-station compatibility
An advertised range figure describes a radio in conditions your aircraft will never fly in. The link you get depends on the margin left after the installation has taken its share, and you can calculate that before ordering.
Three links, and only one of them is this one
An unmanned aircraft usually carries three radio links, and confusing them wastes money in both directions. The RC control link carries pilot input and has to be the most robust. The video link carries the largest data rate and tolerates errors well. The telemetry link is this article's subject: a bidirectional data link carrying MAVLink between the autopilot and a ground control station.
Write down what the telemetry link must do before comparing radios. Live parameter tuning, mission upload in flight and a moving-map display at a useful update rate are a different requirement from a status heartbeat and a position report every second. So is a link that has to carry payload data, which usually should not be on the telemetry radio at all.
Then write the range down as two numbers: the distance at which the link must be reliable, and the distance at which losing it is only an inconvenience because the aircraft carries on and returns. A telemetry link that drops at the far end of a survey line is a nuisance; a control link that drops is an incident. They are not the same specification.
Advertised range and installed range are different numbers
A published range figure is a line-of-sight measurement with favourable antennas, no airframe in the way and no interference. It is a fair way to compare radios, but it does not predict what your aircraft will get. The useful method is a link budget, which is arithmetic you can do on paper in a couple of minutes.
Free-space path loss in decibels is FSPL = 20 log₁₀(d) + 20 log₁₀(f) + 32.44, with distance in kilometres and frequency in megahertz. At 915 MHz over 5 km: 20 log₁₀(5) = 13.98, 20 log₁₀(915) = 59.23, so FSPL = 13.98 + 59.23 + 32.44 = 105.65 dB.
Now spend it. Take a 100 mW transmitter, which is +20 dBm. Lose 1 dB in the aircraft's antenna cable, gain 2 dBi at the antenna, lose the 105.65 dB of path loss, gain 2 dBi at the ground antenna and lose another 1 dB of cable: 20 − 1 + 2 − 105.65 + 2 − 1 = −83.65 dBm arriving at the receiver.
Now the receiver. Holybro publishes the SiK V3's sensitivity as −121 dBm at a 2 kbps RF data rate and −105 dBm at 64 kbps, and 64 kbps is the default. The same radio on the same link therefore has a 16 dB spread in sensitivity, decided by nothing but how fast you asked it to signal.
At the default 64 kbps the margin is −83.65 − (−105) = 21.4 dB. Turned down to 2 kbps it is 37.4 dB: the same hardware and antennas, with 16 dB more margin bought by giving up data rate. That trade is the most useful thing on this page: it is available from a configuration screen after the aircraft is built.
Neither margin is spare capacity. It is the budget from which the airframe blockage, the antenna orientation, the terrain and the interference are all paid, and the next section is the list of what takes its share.
Source: SiK telemetry radio V3What eats the margin, and why more power is the last resort
Airframe blockage. A carbon-fibre airframe is conductive and reflective. An antenna mounted where the fuselage sits between it and the ground station during a banked turn can lose far more than the few decibels people expect.
Polarisation mismatch. Two linearly polarised antennas at right angles to each other are a large loss for free. An aircraft banking through 90° does that to a vertical whip antenna on the ground.
The Fresnel zone. Line of sight is not enough; the radio needs clearance around the straight line too. A link that works at 100 m altitude and fails at 20 m over the same ground usually has this problem. The radio is rarely at fault.
Interference. The shared bands are shared. A site that is quiet on a Sunday morning may not be on a weekday.
Raising transmit power from 100 mW to 1 W adds 10 dB, and is often the most expensive way to get it: it costs current and heat, and in a band with a power limit it may not be legal. Antenna choice, antenna placement and getting the cable run short are usually cheaper and available first. Note too that raising power at one end improves only that direction: the link is only as good as its weaker path.
Frequency band: confirm what you are allowed to use
Holybro sells the SiK Telemetry Radio V3 as separate 433 MHz and 915 MHz part numbers, and they do not work together. A 433 MHz air unit will not talk to a 915 MHz ground unit at any range. Both ends must be the same band, and this is the mistake that turns up when a spare is ordered a year later.
National regulations decide which bands and what transmit power you may use. The product cannot. Confirm the permitted allocation and power limit for your country and for the class of operation before ordering, and record the answer in the project file. In India that is a question for the national spectrum authority and, where the flight is not purely indoor, for the applicable UAS rules.
Physics gives the trade a shape you can reason about: lower frequencies suffer less free-space path loss for the same distance and penetrate obstruction better, while higher frequencies allow smaller antennas and generally more bandwidth. That is why a long-endurance survey aircraft and a short-range inspection quadcopter can both be right with different radios.
Data rate: the number to specify is the one you need
There are two rates in every radio conversation and they are routinely confused. The air data rate is what the modem signals at. The usable throughput is what your MAVLink stream gets after error correction, framing and the return path have taken their share, and it is always the smaller number.
Specify from the ground station's needs. A basic status and position display is undemanding. A full parameter download, a mission upload in flight or high-rate attitude data for tuning is not. On a marginal link you will not see a clean failure. You will see a display that lags, a parameter list that never finishes and a link that seems fine until you need it.
The trade to understand before choosing: a lower air data rate improves receiver sensitivity, and therefore range, at the cost of throughput. A radio that reaches its advertised distance at its lowest rate is not lying, but it is not offering that distance and its highest rate at the same time. Decide which end of that trade your mission is at, and configure both ends to match.
Source: SiK telemetry radio V3Antenna installation is part of the specification
Mount the antenna clear of carbon structure, away from the ESCs and the power harness, with the connector strain-relieved. A coaxial pigtail flexing against a frame edge for fifty flights will start losing the link now and then, which is much harder to diagnose than losing it completely.
Keep the cable run short: loss in a thin pigtail is not negligible at these frequencies, and every decibel spent there is a decibel taken from the margin you calculated. Orient the aircraft and ground antennas to match polarisation in the attitude the aircraft spends most of its time in, and check what happens in a hard turn.
Never power a radio without its antenna connected. And on the ground side, height beats power: lifting the ground station antenna on a mast clears obstruction and Fresnel-zone intrusion in a way that no amount of transmit power will.
Ground-station compatibility and what to send with an enquiry
Check all three interfaces. The aircraft side: which autopilot port, its connector and pinout, and the serial baud rate configured for it. The ground side: how the radio connects to the computer or tablet (USB, serial or a network interface) and whether that computer has a driver and a free port. The software: which ground control station, and whether it is being used with PX4 or ArduPilot.
Radios in our shop are listed as single units and as pairs. A pair is the sensible default for a first aircraft; singles are what you order to add a second ground station, to keep a spare, or to fit a second aircraft to an existing ground unit. Match the band and the firmware configuration across every unit that has to interoperate.
Send us the autopilot and port, the ground station software and host, the intended operating distance and the environment, the band you are permitted to use, and whether you need a single or a pair. That is enough for a shortlist, and for us to spot a mismatch before anything ships.
Source: PX4 companion-computer connectionThe telemetry radios in our shop
Band, power and supply format are what separate these part numbers, and all three are stated in the product listings. Both ends of a link must use the same band, so order the pair or two matching single units.
| Radio | Holybro SKU | Band | Transmit power | Supplied as |
|---|---|---|---|---|
| SiK Telemetry Radio V3 100 mW 433 MHz | 17012 | 433 MHz | 100 mW | Single |
| SiK Telemetry Radio V3 100 mW 915 MHz | 17013 | 915 MHz | 100 mW | Single |
| SiK Telemetry Radio V3 1 W 915 MHz | 17030 | 915 MHz | 1 W | Single |
| SiK Telemetry Radio V3 1 W 915 MHz | 17031 | 915 MHz | 1 W | Pair |
| Microhard P900 | 17035 | 900 MHz band | — see specification | Single |
| Microhard P900 | 17036 | 900 MHz band | — see specification | Pair |
| Microhard P400 | 17037 | 400 MHz band | — see specification | Single |
| Microhard P400 | 17038 | 400 MHz band | — see specification | Pair |
Part numbers, band, power and single-or-pair format are from the Holybro price list behind our shop listings; where the band appears in the model name it is reproduced as the manufacturer states it. A dash means we do not hold the figure; it does not mean zero. For output power, sensitivity and air data rates on the Microhard P400 and P900, use the manufacturer's documentation for your model. The SiK V3 figures used in the worked example above are Holybro's own, cited there. Confirm the permitted band and transmit power with your national regulator before ordering. A manufacturer's product page cannot tell you.
Source: SiK telemetry radio V3Where the link budget is spent
The worked example above, drawn out. Read it left to right: the only figure that improves with a bigger radio is the first box, and the margin at the end is what every installation problem is paid for from.
Products discussed
The parts this guide names.
Specifications on each page are the manufacturer's. Confirm the exact variant and document revision before ordering.
SiK Telemetry Radio V3 1 W 915 MHz (Pair)
Both ends, matched band and power. SKU 17031.
SiK Telemetry Radio V3 100 mW 433 MHz
433 MHz single unit. SKU 17012.
Microhard P900 Pair
900 MHz band pair. SKU 17036.
2.4 GHz / 900 MHz dual-band T antenna
IPEX1 antenna option. SKU 32010.
All telemetry radios and antennas
The full range, with every band and supply format.
Sources & basis
What this is based on.
- Part numbers, band, transmit power and single-or-pair supply format for the SiK Telemetry Radio V3, Microhard P900 and P400 ranges as listed in the Vebix Automation shop.
- Free-space path loss, FSPL(dB) = 20 log₁₀(dkm) + 20 log₁₀(fMHz) + 32.44, from standard radio propagation. The transmit power, cable losses and antenna gains in the worked example are stated assumptions; the receiver sensitivity figures are Holybro's own, cited on the page.
- Permitted frequency bands and transmit power are set by national regulation and are not stated here; confirm them with the relevant authority for your country and class of operation.
- SiK telemetry radio V3 (accessed 2026-09-07)
- PX4 companion-computer connection (accessed 2026-09-07)
Published 7 September 2026. Last revised 7 September 2026. Corrections to sales@
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Specifying a telemetry link?
Send your autopilot and port, ground-station software and host, intended operating distance and the band you are permitted to use, and we will return a compatible component shortlist including antennas and cables. Request a component quotation for supply in India.
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