RF interference is affecting my node — how do I diagnose it

RF Interference Is Affecting My Node — How to Diagnose It

LoRa spread-spectrum modulation gives it excellent resistance to narrowband interference, but it is not immune. If your node is experiencing unexplained packet loss, poor RSSI from nearby nodes, or erratic behavior that does not correlate with distance or obstacles, RF interference may be the culprit.

Symptoms of interference

• High SNR variation: A node 500m away that normally delivers SNR of -5 dB suddenly shows -15 dB or worse for no physical reason. If SNR fluctuates wildly over minutes without any change in node position, an external RF source is likely corrupting packets.
• Unexpectedly poor RSSI from nearby nodes: RSSI that is 20–30 dB worse than expected given distance and antenna gain suggests wideband noise is raising the noise floor.
• Time-of-day failure patterns: If failures cluster during business hours, when appliances run, or at regular intervals (e.g., every 30 minutes), a duty-cycling device such as a smart meter network is a likely source.
• One direction fails more than others: If nodes in one geographic direction consistently perform worse, a directional interference source may be oriented toward your antenna.

Diagnosis tools

The most effective way to see what is happening in the 902–928 MHz band is with a Software Defined Radio (SDR):

• Hardware: An RTL-SDR dongle (~$25 USD) with a 915 MHz antenna is sufficient. Higher-end options like HackRF or Airspy offer better sensitivity.
• Software: SDR# (Windows) or GQRX (Linux/macOS) — both are free. Open the spectrum analyzer view and zoom to 902–928 MHz.
• What to look for: Constant carriers (a vertical spike that never moves) indicate a narrowband source. Sweeping signals suggest frequency-hopping devices such as cordless phones. Periodic bursts at regular intervals suggest smart meter networks (ITRON, Sensus, etc.) which use this band extensively in North America.

Common interference sources in the 902–928 MHz band

• Baby monitors (many analog and digital models use 900 MHz)
• 900 MHz DECT cordless phones (older models)
• Smart meter networks (AMI/AMR systems from utilities)
• Industrial wireless sensors and SCADA equipment
• Some older Wi-Fi extenders and video senders

Mitigation strategies

• Change channel number in Meshtastic: Meshtastic allows you to select different channel frequencies within the ISM band. If a specific frequency is congested, switching to an alternate channel preset (e.g., LongFast vs. LongSlow vs. MedFast) shifts your center frequency away from the interference.
• Use a directional antenna: A Yagi or patch antenna pointed toward your intended mesh nodes, and away from the interference source, provides front-to-back rejection of 15–20 dB.
• Relocate the antenna: Moving the antenna even a few meters can place a building or terrain feature between your node and the interference source, providing significant shielding.
• Reduce antenna height: Counter-intuitively, lowering an antenna can reduce pickup of distant interference while maintaining adequate coverage of nearby nodes.