Radio Modems

Radio modems are used to transmit the current position, battery voltage and similar properties to the ground. The PX4 autopilot can be flown without in manual mode, but for setup and advanced features a telemetry link is absolutely necessary.

A radio modem always needs a base station, so at least one pair is required. Depending on the type of the radio modem one base station per vehicle or per group of vehicles is required.

Experiencing issues on Windows where the radio modem is detected as mouse? Unfortunately this is a defect in the way Windows handles serial mice and not a problem of the radio modem. Either connect the radio modem to the Windows machine before sending any data from the aircraft, or disable the support for serial mice in Windows.

433 MHz Antennas

The antennas here fit all 433 MHz radios. Some might need adapters (e.g. 3DR's odd choice of RP-SMA for the connector requires an adapter).

Diamond SRH771 1/2 wavelength monopole

A great monopole for usage on the ground:

  • Diamond SRH771 (TBS Store)
  • IMPORTANT: For the use with a 3DR radio, get one of these RP-SMA adapter:

1/4 Monopole

This small and light antenna is great for onboard usage.

  • 1/4 Monopole (TBS Store)
  • IMPORTANT: For the use with a 3DR radio, get one of these RP-SMA adapter:

433 MHz / 868 MHz / 900 MHz Long Range / Outdoor

3DR USB Radio

Firmware Upgrade Reference for Developers (Mac OS)

Install SDCC

brew install sdcc
# in case there is a link error, you can resolve it by issuing:
# brew link --force xdcc

compile the firmware

git clone https://github.com/tridge/SiK.git
cd SiK/Firmware
make install

upload it to the radio (adjust the serial port name):

tools/uploader.py --port /dev/tty.usbserial-CHANGETHIS dst/radio~hm_trp.ihx

Note: The red led first blinks, then becomes solid during programming. After the successful reboot the green led should come on (blinking if the 2nd radio of the pair is off, solid if they are in sync).

AT Commands / Set the net ID

Connect to the radio modem serial port with these settings:

* 57600 baud rate * No parity * 8 data bits * 1 stop bit

On a *nix system screen does the job:

screen /dev/tty.usbserial-CHANGEME 57600 8N1

Then start command mode:

DO NOT TYPE ANYTHING ONE SECOND BEFORE AND AFTER

+++

List the current settings:

ATI5

Then set the net ID, write settings and reboot radio:

ATS3=55
AT&W
ATZ

You might have to power-cycle the radio to connect it to the 2nd radio


jDrones Long-Range Telemetry Set

jDrones offers long-range RFD sets as fully ready made, Plug-N-Play sets for Pixhawk and other users. Modules have all power filtering, level and USB adapter eg. everything needed to connect them to your vehicle. Their firmware is optimized for MAVLink communications and low-latency telemetry use.

These long-range modems are based RFDesign modules and offers easily over 5km ranges with normal antennas without dropping signal.

There are two versions available:

RFDesign RFD900

The RFDesign RFD900 is protocol- and firmware-compatible with the 3DR Radio, but offers substantially greater range. You can mix and match the two (e.g. a 3DR Radio on the vehicle and an RFD900 at the base station) as well.

RFDesign RFD900


2.4 GHz 3DR WiFi telemetry

The 3DR WiFi telemetry module is running a Lua-based firmware, NodeMCU, and three .lua files stored in the module memory. init.lua, config.lua, setup.lua

Change the module configuration

Download the ESPlorer program, follow the instruction on the website to install it and then run it.

To run it on Linux type:

java -jar ESPlorer.jar


  1. Connect your module by USB, set baud rate to 9600 and click open.
  2. Under NodeMCU+MicorPython select the tab Snippets, and Edit the Snippet0 to Config with the command advancedconfig and click Run.
  3. Download the configuration file: config and extract it.
  4. In the tab Scripts open the early downloaded file config.lua.
  5. Set your desired SSID and password.
  6. Click save to ESP.

Restart the module, you should now be able to connect with the module with your new SSID and password.


2.4 GHz Short Range / Indoor / Vicon

For indoor or short range setups, the use of the Lairdtech PRM123 module is recommended for control channels, since its very reliable and has a low latency. The Roving Networks WiFly modules are recommended for sending back the telemetry data, as its bandwidth is very high and multiple modules can be easily set up with one Wifi Router.

Adapters

All modules listed below use the XBee pinout. These adapters can be used to connect them onboard or offboard via USB:

Lairdtech Proprietary

Developer Kit

More resources and Firmware files

Roving Networks WiFly UART to WIFI bridge

The Roving Networks WiFly modules deliver up to 1 MBit/s (921600 baud) of UART to UDP or TCP/IP bandwidth. The range is limited (as with any Wifi device), but the modules are very helpful for high-bandwidth tests if a lot of telemetry data has to be pushed through the link.

Digi XBee Proprietary

Wiring

Wiring these modules to the adapter is standard and straightforward:

  • Pixhawk 5V ↔ Module 5V (make sure to use a regulated adapter!)
  • Pixhawk RX ↔ Module TX
  • Pixhawk TX ↔ Module RX
  • Pixhawk RTS ↔ Module CTS
  • Pixhawk CTS ↔ Module RTS
  • Pixhawk GND ↔ Module GND

NOTE: Leave RTS and CTS unconnected if the module does not support hardware flow control or its disabled (if it does support it, connecting them is highly recommended). The standard Pixhawk pinout is on this page: Pixhawk Autopilot.

WIFI Access Points

The PIXHAWK and sFly ETH projects have tested a wide range of access points (including multiple models from Linksys, Cisco, Netgear and D-Link. The most reliable model and the one with the best range is the D-Link DIR-825.

ASUS RT-AC66U

Rock-solid ASUS router with great reviews. Extra long antennas:

This model is rock-solid and well-proven even in outdoor setups at -15 deg. Celsius.

There are a number of important settings on this device, see the D-Link DIR-825 Settings page.

Ground Stations

An example for a ground station / radio tripod can be found here.

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