3DR Radio Manual

The 3DR Radio (version 2) is the easiest way to setup a telemetry connection between your 

APM/Pixhawk and a ground station. This article provides a basic user guide for how to connect 

and configure your radio.

3DR Radio v2 

Contents

 1 Overview

 2 Status LEDs

 3 Connecting the radios

o 3.1 Connecting to Pixhawk

o 3.2 Connecting to APM2.x

o 3.3 Connecting to a PC

o 3.4 Connecting to an Android tablet

 4 Configuring using the Mission Planner

 5 Expected range

o 5.1 Diagnosing range issues

 6 Improving the range

 7 Support for different countries/regions

 8 3DR Radio Discussion Forum

Overview

The 3DR Radio is the easiest way to setup a telemetry connection between your APM/Pixhawk 

and a ground station. It is small, light and inexpensive, and typically allows ranges of better than 

300m “out of the box” (the range can be extended to several kilometres with the use of a patch 

antenna on the ground). The radio uses open source firmware which has been specially designed 
to work well with MAVLink packets and to be integrated with the Mission Planner, Copter, 

Rover and Plane.

The radios can be either 915Mhz or 433Mhz and you should purchase the model which is 

appropriate for your country/region.

The main features of the 3DR Radio are listed below (see the Advanced Configuration for more 

information):

 Very small size

 Light weight (under 4 grams without antenna)

 Available in 900MHz or 433MHz (v2 only) variants

 Receiver sensitivity to -121 dBm

 Transmit power up to 20dBm (100mW)

 Transparent serial link

 Air data rates up to 250kbps

 MAVLink protocol framing and status reporting

 Frequency hopping spread spectrum (FHSS)

 Adaptive time division multiplexing (TDM)

 Support for LBT and AFA

 Configurable duty cycle

 Built-in error correcting code (can correct up to 25% data bit errors)

 Demonstrated range of several kilometres with a small omni antenna

 Can be used with a bi-directional amplifier for even more range

 Open source firmware

 AT commands for radio configuration

 RT commands for remote radio configuration

 Adaptive flow control when used with APM

 Based on HM-TRP radio modules, with Si1000 8051 micro-controller and Si4432 radio 

module

Status LEDs

The 3DR Radios have 2 status LEDs, one red and one green. The meaning of the different LED 

states is:

 Green LED blinking – searching for another radio

 Green LED solid – link is established with another radio

 Red LED flashing – transmitting data

 Red LED solid – in firmware update mode

Connecting the radios
The 3DR Radio v2 has interchangeable air and ground modules, meaning that you use them as a 

pair but it does not matter which one goes on the vehicle and which remains on the ground.

The radio has a micro-USB port, and a DF13 six-position port. The following sections explain 

how to connect these to flight controllers and ground stations.

Connecting to Pixhawk

Use the 6 pin DF13 connector that should have come with the radio to connect the 3DR radio to 

your Pixhawk’s “Telem 1′′ (“Telem 2′′ or “Serial 4/5′′ can also be used but the default 

recommendation is “Telem1′′).
Connecting to APM2.x

Use the 6-to-5 pin DF13 connector to connect the 3DR radio to your APM2’s Telem port. 

Because of the limited number of serial ports on the APM2.x, the telemetry radio cannot be used 

while the board is also plugged in with the micro USB port.

Connecting to a PC

Connecting the 3DR radio to your Windows PC is as simple as connecting the micro USB cable 

(which should have been included with the radio) to your PC. The necessary drivers should be 

installed automatically and the radio will appear as a new “USB Serial Port” in the Windows 

Device Manager under Ports (COM & LPT). The Mission Planner’s COM Port selection dropdown should also contain the same new COM port.
To connect the radios:

 Select the new COM port, set the baud rate drop down (which appears between the COM 

port and Connect buttons) to 57600.

 Press the Connect button and if the two radios connect successfully you should be able to 

lean your vehicle left and right and see it’s attitude update on the MP’s Flight Data 

screen’s artificial horizon.

Connecting to an Android tablet

Connecting the 3DR radio to an Android tablet using the L shaped micro USB cable (which 

should have been included with the radio). Then follow the directions in your preferred Ground 

Station app.

Configuring using the Mission Planner

APM Mission Planner supports configuring your 3DR radios using a simple GUI interface.

Tip:

Many users will not need to configure their radios! One case where you might do so is when you 

use your vehicle with others — in which case you will need to specify different radio channels 

(Net ID).

To make changes:

 Connect one of the 3DR radios to your computer using the micro USB cable.

 Power the radio attached to the vehicle by plugging in the vehicle’s battery.

 Open the Mission Planner and go to the Initial Setup >> Optional Hardware >> 3DR 

Radio page.

 Select the correct COM port and set the baud rate to 57600. Ensure the “Connect” button 

is in a disconnected state as shown in the image below..

 Press the Load Settings button and both the Local and Remote areas should fill in with 

values including the firmware Version
 The most common entry to change is the Net ID. The default is 25 for all 3DR radios but 

if you plan to fly in an area with other pilots who may be using the same radio it is best to 

change this to another number.

 After making changes, click the Copy Required Items to Remote and press Save 

Settings

Other parameters you may choose to update:

 Baud (default 57) : the rate at which the mission planner or vehicle communicates with 

the local radio. “57” = 57600 bits per second.

 Air Speed (default 64) : the rate at which the two radios will communicate with each 

other. “64” = 64kbps (kilobits per second). Setting a lower rate will increase the range of 

the radio but reduce the rate of data (i.e. the amount of data that can be sent in a given 

time) across the link.

 ECC (default is “on”): controls whether error correction is on or off. When on “12/24 

Golay error correcting code” is used which involves sending a 16 bit CRC byte along 

with the data to ensure that bad data is thrown away. Unfortunately this also halves the 

data rate across the link but it is recommended to leave ECC on especially when when the 

vehicle is far from home base because transmission errors increase greatly with distance.

 MAVlink (default is “MAVLink”) : this controls whether the transmission is optimised 

for MAVLink packets or not. Set to “Low Latency” if using a joystick or an android 

tablet’s virtual joystick to manually fly the vehicle. Note that information on the radio 

signal strength (rssi) and error rate is only sent if this parameter is set to it’s default, 

“MAVLink”.

 Tx Power (default 20) : the transmission power where 1=1.3milliWats, 2=1.5mW, 

5=3.2mW, 8=6.3mW,11=12.5mW, 14=25mW, 17=50mW, 20=100mW. This should be 

set to conform with your local regulations. Some per-country information is below.

 Duty Cycle (default 100) : the maximum percentage of time that the radio will transmit

packets. Some regions of the world allow for higher transmit power or more frequencies 

if you have a duty cycle below a given threshold. So for example in Europe you can 

transmit on a wider range of frequencies in the 433 band if your duty cycle is below 10%. 
Telemetry traffic is quite ‘bursty’, so the average transmit time is not generally high. 

When you set a duty cycle below 100% then your available bandwidth will be reduced, 

so you will find it will only work well for telemetry at higher air speeds. A radio can be 

set to receive only by setting it’s Duty Cycle to zero.

 Max Window (default 33) : ensure the GCS can send a packet to the vehicle ever 33msec. 

This should be kept as a low number (like 33) when the “MAVLink” setting is “Low 

Latency”

 LBT Rssi (default 0) : holds the threshold used for “listen before talk” which allows it to 

comply with some country’s regulatory requirements. When non-zero the radio listens for 

quiet period of time where no signals from other radios are received before transmitting. 

This parameter holds the receiver signal strength below which the airwaves are 

considered “quiet”. If this param is set to zero then LBT is disabled. Setting this to 25 

(the min) is -121 dBm. Each increment above 25 raises the threshold by about 0.5dB so 

for example 40 equals a signal strength of 7.5dB. The full formula is: 

signal_dBm = (RSSI / 1.9) - 127

The LBT implementation in the 3DR radio uses a minimum listen time of 5ms, plus 

randomised listen time as per the European 9.2.2.2 rules. Note that in many regions you 

need to implement LBT in conjunction with AFA (Adaptive Frequency Agility). The 

3DR Radio implements AFA as long as you have NUM_CHANNELS set to more than 1.

Expected range

Typical range achieved with the 3DR radios using standard configuration and antenna is around 

500m, but the range varies a lot depending on noise sources and antenna setup.

Diagnosing range issues

The first thing you should do when diagnosing range issues is the “one meter test”. Setup the two 

radios one meter apart and look at the local and remote RSSI. You should get a value of over 190 

for a standard 3DR radio. If you don’t then your antennas may be faulty or your radios may have 

been damaged. If you have ever run the radios without an antenna attached them the radio may 

have been damaged.

If that test passes then have a look at your local and remote RSSI and noise from a flight. See the 

advanced setup page for detailed information on diagnosing range issues using telemetry logs.

Improving the range

The range can be improved by:

 Using a small “patch antenna” on the ground like this flat patch antenna or this Yagi 

antenna perhaps mounted on an Antenna Tracker
 Replace at least one of the two 3DR radios with a higher powered RFD900

 Reduce the AirRate parameter which will increase range but at the expense of the rate of 

the data transfer.

The graph below shows the ground and remote receiver strength vs distance from home (in 

meters) for a test flight of a 3DR radio on a SkyFun plane. The ground based radio was attached 

to a 3.5dB flat patch antenna. The SkyFun had a small ‘wire’ antenna. The graph shows the 

vehicle reached a distance of nearly 3km and the link was completely maintained throughout the 

flight.

Although anecdotal, another user provided a Tlog showing a good link kept while the vehicle 

was 4.5km from the base station, using default radio settings for a 3DR 900 radio. The plane 

used a small omni antenna, and a 8dB patch antenna on the ground station.

Support for different countries/regions

It is very important that you configure your 3DR Radios to comply with your regional/country 

regulations for frequency, hopping channels and power levels. The table below provides links to 

the applicable standards for users without any special license. If you are have an application 

specific license or have a HAM license then you should know what rules are applicable to you.

Note:

Compliance is your responsibility. The 3DR radio is a ‘DIY’ radio part and you need to ensure 

what whatever you build meets local regulations. Please check your local rules carefully.

Region Radio 

Model Settings Standard

USA 3DR 

900

MIN_FREQ: 902000

MAX_FREQ: 928000

NUM_CHANNELS=50

FCC 15.247

Canada 3DR MIN_FREQ: 902000 RSS-210 Annex 8.1
900 MAX_FREQ: 928000

NUM_CHANNELS=50

Australia 3DR 

900

MIN_FREQ: 915000

MAX_FREQ: 928000

NUM_CHANNELS>=20

LIPD-2000 item 52

Australia 3DR 

433

MIN_FREQ: 433050

MAX_FREQ: 434790

TXPOWER<=14

LIPD-2000 item 17

Europe (most 

countries)

3DR 

433

MIN_FREQ: 434040

MAX_FREQ: 434790

TXPOWER<8

NUM_CHANNELS>30

ETSI EN300 220 7.2.3

Europe (most 

countries)

3DR 

433

MIN_FREQ: 433050

MAX_FREQ: 434790

TXPOWER< 8

DUTY_CYCLE 10

ETSI EN300 220 7.2.3

United 

Kingdom

3DR 

433

MIN_FREQ: 433050

MAX_FREQ: 434790

TXPOWER<8

DUTY_CYCLE 10

IR2030/1/10

New Zealand 3DR 

900

MIN_FREQ: 921000

MAX_FREQ: 928000 Notice 2007, Schedule 1

New Zealand 3DR 

433

MIN_FREQ: 433050

MAX_FREQ: 434790 Notice 2007, Schedule 1

Brazil 3DR 

433

MIN_FREQ: 433000

MAX_FREQ: 435000

TXPOWER<=8

ANATEL – Resolução no 506/2008

Brazil 3DR 

900

MIN_FREQ: 902000

MAX_FREQ: 907500

NUM_CHANNELS>=11

ANATEL – Resolução no 506/2008

Brazil 3DR 

900

MIN_FREQ: 915000

MAX_FREQ: 928000

NUM_CHANNELS>=26

ANATEL – Resolução no 506/2008

Argentina 3DR 

900

MIN_FREQ: 902000

MAX_FREQ: 928000 Comisión Nacional de Comunicaciones

South Africa 3DR 

433

MIN_FREQ: 433050

MAX_FREQ: 434790

TXPOWER<=10mW

2008 RR 5.138, Government Gazette No 

31127,Notice No 713 of 2008 and Government 

Gazette No 31290,Notice No 926 of 2008 refer