If you find that your wattage is fluctuating (dropping to zero and/or spiking), or you see your sensors showing up as having "no signal" on the pairing screen, it's likely that Zwift isn't receiving all of your data packets due to your ANT+ signal receiving interference.
ANT+ is locked to a single frequency, and much like other wireless signals, operates on the 2.4 GHz band - and because it's a low power lossy protocol, it's more likely to lose packets the more "noise" there is around it. Any time eight packets are missed in a row, the radio considers itself "disconnected" and goes into search mode to resync. This shows up in Zwift with the symptoms described above.
As ANT+ signal interference isn't a Zwift problem, but a problem with your setup/environment, this isn't an issue we can fix (as much as we wish we could!). Zwift only reads the data that's being sent to it.
While we can't solve this on our end, we've included the most common causes for interference and dropouts that we've seen so you can try going through a process of elimination and find the issue.
Here are the 8 most common causes we see for ANT+ dropouts:
Note that many of these issues can be solved by moving your ANT+ dongle closer to your sensors with a USB extension cord, and we highly recommend trying this first.
- Physical distance: We highly recommend keeping your ANT+ dongle and sensors less than three feet apart - and the closer, the better. A USB extension cable is an easy way to do so.
- Dying battery: If you haven't replaced your battery recently, try swapping in a new one.
- Wireless signal interference: This includes any devices that transmit wireless signals or electromagnetic fields. See our example list at the bottom of the article.
- Fans: These generate an electromagnetic field around them that can block signals if located between your ANT+ dongle and sensors. Position it so it's not in a direct line or near either one of these.
- Wireless computer accessories: The USB dongle for your wireless mouse, keyboard, or other accessory can cause interference, especially if it's next to the ANT+ dongle on the computer.
- Loose USB connection: Make sure your ANT+ dongle is firmly plugged in.
- Physical barriers: Any object that obscures line of sight from your ANT+ dongle to your sensor can cause packet loss. Try to keep a clear path from your dongle to your sensors.
- Hardware failure: If you still experience issues after eliminating these factors, it's likely that your ANT+ dongle, sensors, or USB cord (if applicable) is dying/dead. In this case, you may want to try borrowing a replacement from a friend to test with and verify. Or if your device supports Bluetooth, you can try connecting over BLE to eliminate the possibility that the problem is with the ANT+ dongle or USB cord.
Here's a list of potential wireless signal interference sources:
- Bluetooth headphones, speakers, or hearing aids
- WiFi router (if possible, set the router to a fixed channel on the low end of the spectrum, like channel 3, to prevent potential conflicts between your computer/iOS and ANT+ devices)
- Microwave ovens
- Direct Satellite Services (the coaxial cables and connectors can cause interference)
- Power sources (includes power lines or a breaker box in a wall)
- Cordless telephones
- Wireless video transmitters (e.g. Chromecast, AirPlay, etc.)
- Wireless speakers
- Certain external monitors and LCD displays
- Any devices that use a cable to connect to a computer or power source
- Anything else that transmits a wireless signal, from routers to baby monitors
If you're still experiencing dropouts after eliminating those causes, we can try and help you investigate. Just send all the files located in your \Documents\Zwift\Logs folder, along with some pictures of the location of your trainer, your sensors, and your ANT+ dongle, to https://support.zwift.com/hc/en-us/requests/new. If we can't solve the problem, we may be able to at least point you in the right direction.