High Background Noise Error and How to Resolve it

What is the High Background Noise error?

If the transponder reports a high background noise level, it typically indicates that the vessel is in an area with a high background noise level or an AIS channel blocker. It is more likely a noise source onboard the vessel.

The high background noise error is an international standard for the Class B AIS IEC 62287 and is a requirement. The purpose is to alert the user of a blocker, local noise on the channel, or adjacent channel. The alert notifies the user as it affects the AIS system integrity. It averages the noise levels over a minute, so a high level in itself doesn't mean all messages are necessarily blocked. The user may notice that the AIS receiver performance will degrade.

Causes of high background noise

The LED noise created in the power supply switching of a tri-color masthead can end up in the VHF marine bandwidth and add a significant amount of noise on AIS channels when the location of the LEDs are near the VHF antenna.

Troubleshooting background noise level source using the advanced AIS settings screen (Vision, iOS app) or the status page in vmAIS. Look for high levels of RSSI on either channel. If both channels report high (>-77dBm), the noise source is likely wideband. Possible sources are a tri-color LED or other electronics on board. Turn potential noise sources on and off and look for any difference in the RSSI reading (allowing time to settle its average).