Tutorial ANTplus sensors

Tutorial: ANT+ sensors

What it is. ANT+ is a low-power wireless protocol used by heart-rate straps, bike speed, cadence and power sensors, footpods, environment sensors and sports watches, on 2457 MHz. OnAir hears the open broadcasts a watch or bike computer would hear and shows the device, its data pages and its battery.

Read this first. Receive only: nothing is sent, paired or acknowledged. Heart rate and other body data belong to the wearer; do not share what you receive from other people. Check your local rules. See Legal and Privacy.

What you need

• A radio that reaches 2.4 GHz at 4 Msps. The mode asks for and needs 4 Msps. An RTL-SDR cannot do it; a HackRF, PlutoSDR, LimeSDR or BladeRF can.
• A 2.4 GHz antenna.
• Frequency: 2457 MHz (ANT+, in the database as sports and fitness sensors). The mode tuning range is 2400 to 2524 MHz for other ANT networks.

Before you start

Sensors are close and low power. The 2.4 GHz band is crowded with Wi-Fi and Bluetooth, so keep gain moderate. Sensors only transmit when worn or moving; a strap needs to be on the skin to report a heart rate.

Step by step

1. In the mode list open IoT & sensors and choose the ANT+ entry (ANT+ sensors on 2457 MHz).
2. Choose the radio at 4 Msps and start the receiver.
3. Press ANT+ 2457 MHz to tune the ANT+ channel. Tick Also other ANT networks (not only ANT+) to hear sensors on other ANT channels in your tuned range.
4. Move the sensor (start a bike wheel, wear the strap).

What you should see

Sensors list with a device number and type, then the data pages: heart rate with beat count and R-R interval, plotted over time; power, cadence, speed, temperature; manufacturer, serial and battery.

Reading the screen

• Sensor view: Sensors table (Type, device number, Heard, Value) and a plot (with Auto range). If a strap is not worn, the panel says there is no heart rate (the strap is not on the skin) or waiting for a second frame.
• Frames view: UTC, Channel, Payload, Decoded and dBFS for each message.

Options and settings

Auto range scales the plot. Clear forgets the sensors. A synthetic source can be chosen to try the screens.

Troubleshooting

• Nothing heard. Check the radio really reaches 2.4 GHz at 4 Msps. Bring the sensor closer.
• Device seen but no heart rate. The strap is not worn or sends other pages first.
• Many errors. Wi-Fi interference; change position.
• Different frequency. Tick Also other ANT networks.

Tips

Start with a bike speed sensor: spin the wheel and watch it appear.

Legal and privacy notes

Passive. Personal health data of others is private.

Under the hood

GFSK at 1 Mbit/s on 2457 MHz; messages of eight bytes (a data page). Device pages follow the ANT+ device profiles.

Related

Mode-ANTplus-sensors, Tutorial-Bluetooth-LE, Tutorial-Zigbee-802-15-4, Tutorial-ISM-sensors, Modes, Main-window, Supported-radios, Troubleshooting, FAQ, Legal.