Quick Answer
A telemetry radio sends flight data, such as GPS position, battery voltage, and speed, from a drone to a ground station using a low-frequency radio link. It uses a pair of radios, one on the drone and one on the ground, and works alongside the separate radio that controls the drone.
What Telemetry Actually Sends
Telemetry is a stream of small data packets. On most autopilot drones, this data uses a protocol called MAVLink, which packages readings like altitude, heading, GPS lock, and battery level into a format ground stations can read.
MAVLink also carries commands the other way, such as changing a flight mode or sending a new waypoint. This two-way flow is what lets you watch and manage a drone from far away, not just fly it.
Why Telemetry Needs Its Own Link
A drone already has a control link for steering it. Telemetry could ride on that same link. Many builders instead add a separate telemetry radio, because dedicated telemetry radios reach further and carry more data than a typical RC radio's telemetry feature.
Autopilot systems like ArduPilot and PX4 are built around this separate telemetry link. It plugs into a serial port on the flight controller, often labeled TELEM1 or TELEM2 on a Pixhawk-style board.
Frequency Bands and Why They Matter
Telemetry radios commonly run on 433 MHz, 868 MHz, or 915 MHz, depending on your region's rules. Lower frequencies travel further for the same power because they bend around obstacles and buildings better than higher frequencies.
The trade-off is data rate. Lower frequencies and longer range usually mean less data per second. A radio built for range will send position updates less often than one built for speed.
Regional rules decide which bands you can legally use, and at what power. Always check your local telecom authority before choosing a radio, since a band that is legal in one country may be restricted in another.
Data Rate vs Range
Every telemetry radio balances two things: how much data it sends, and how far that data can travel. Push the data rate up, and range usually drops. Push the range up, and you send less data per second.
For most drone missions, a modest data rate is enough. You mainly need position, battery status, and basic health data, not a video feed. That is why telemetry radios can achieve much longer range than video links running at the same power.
Air Unit and Ground Unit
Every telemetry radio setup has two halves. The air unit mounts on the drone and connects to the flight controller's telemetry port. The ground unit connects to a laptop, tablet, or dedicated ground station running software like Mission Planner or QGroundControl.
Both units must match on frequency, air data rate, and Net ID, which is a code that keeps nearby radios from talking to the wrong drone. Mismatched settings are the most common reason a telemetry link fails to connect. Our RFD900 setup guide walks through matching these settings step by step.
Choosing a Radio for Your Range
Start by asking how far you actually need the link to reach. A radio built for a few kilometers is lighter, cheaper, and simpler than one built for tens of kilometers.
| Need | Good Fit |
|---|---|
| Short range, simple setup | Basic 433 MHz or 915 MHz telemetry radio |
| Mid to long range | RFD900-class radio |
| Video and telemetry together | IP-based radio such as Microhard |
If you need both telemetry and control on one link, look at combined solutions like the RFD TXMOD. If you want to compare specific radio models, see our RFD modem comparison.
Whatever radio you choose, confirm its transmit power and frequency are legal in your country. Power limits and license rules are set locally, not by the radio maker.
Setting Realistic Expectations
No telemetry radio guarantees a fixed range in every setting. Trees, hills, buildings, and even the angle of your antennas all change real-world performance. Manufacturer range figures are usually measured in open, flat terrain with a clear line of sight.
Build in a safety margin. Test your link at a shorter distance first, watch how the signal quality changes as you move away, and never fly further than you have already proven the link can handle.
Logging Telemetry for Later
Most ground station software can save telemetry data to a log file as you fly. This log records the same data your screen shows: position, altitude, battery voltage, and flight mode, all with a time stamp.
A saved log is useful after the flight, not just during it. You can review a flight path on a map, check where battery voltage dropped fastest, or spot the exact moment a link had trouble. This is especially helpful when you are still tuning a new long-range setup, since it shows you real numbers instead of guesses.
Keep your logs organized by date and by which drone or radio setup you used. Over time, comparing logs from different flights helps you see if a change to your antenna, radio settings, or flight route actually improved your range or link quality.