Field Guide · protocol

Also known as: ANT, ANT+, ANT plus

ANT+ is an ultra-low-power 2.4 GHz wireless protocol built for fitness and health sensors, layering standardised “device profiles” on the underlying ANT radio, which uses GFSK modulation.1 It is the technology that links a heart-rate strap, cycling power meter, or cadence sensor to a bike computer or watch, and it long predated (and now coexists with) Bluetooth LE in the same role.

HRsensor watch bike computer phone app one broadcast sensor → many receivers
An ANT+ sensor broadcasts once and can be received by several displays at the same time, unlike a one-to-one paired link.

Overview

ANT is a proprietary but openly documented protocol from Dynastream (a Garmin company). Its radio sends short (~8-byte) messages using GFSK at 1 Mbit/s on the 2.4 GHz band, coordinated by an “adaptive isochronous” scheme: channels transmit in scheduled slots and shift timing to avoid colliding, letting many independent sensor networks share the air. A hallmark is broadcast operation — a heart-rate sensor can transmit to a watch, a bike computer, and a phone simultaneously, without pairing to each. ANT+ is the interoperability layer: agreed device profiles (heart rate, bike power, speed/cadence, running dynamics) that guarantee any ANT+ display understands any ANT+ sensor of that type.

Technical characteristics

Property Value
Band 2.4 GHz ISM
Modulation GFSK
Bit rate 1 Mbit/s (short messages)
Access Adaptive isochronous TDMA channels
Message size ~8 bytes payload
Topology Broadcast, star, mesh, shared channels

The extreme frugality — a sensor can run for years on a coin cell — comes from tiny, infrequent messages and a very simple radio, trading throughput for battery life.

History

Dynastream introduced ANT in 2004 and the ANT+ interoperability profiles around 2008. Garmin’s acquisition entrenched it across sports electronics. Many modern sensors now transmit ANT+ and Bluetooth LE at once so they work with both ecosystems.

Deployment

ANT+ is ubiquitous in cycling, running, and fitness equipment — power meters, heart-rate straps, indoor trainers, and gym machines — where its broadcast-to-many model and low power suit multiple simultaneous displays. BLE has eroded its exclusivity but not displaced it in serious sports gear.

Decoding it with GopherTrunk

GopherTrunk does not decode ANT+. Its 2.4 GHz GFSK, adaptive channel timing, and proprietary framing sit outside GopherTrunk’s land-mobile decode chain; enthusiasts use dedicated ANT USB sticks or SDR flow graphs for it. It is unrelated to GopherTrunk’s trunking and aeronautical targets.

Sources

  1. ANT (network) — Wikipedia, on the ANT/ANT+ ultra-low-power sensor protocol, its 2.4 GHz GFSK radio, adaptive isochronous channels, and device profiles. ↩

See also