Interference Sources at 433 MHz

The 433 MHz ISM band is shared with a lot of equipment. Knowing the neighbors helps you interpret false hits in SEARCH mode.

The usual suspects

Source	Frequency	Notes
Garage door openers	~433.92 MHz	Classic false hit
Key fobs and car remotes	433-434 MHz	Burst transmissions
Wireless weather stations	433.05-434.79 MHz	Continuous data bursts
Doorbell transmitters	433 MHz	Random bursts
Smart-home sensors	433 MHz	Frequent short packets
LTE/5G harmonics (rare)	Near the band	Usually below noise floor
LED drivers, switching supplies	Broadband	Localized, near the device

What a false hit looks like

In SEARCH mode you see a hit with a rising RSSI, but no Morse. The audio pitch may jump around as the interferer transmits its data bursts. The hit log fills with frequencies that are “busy” but not beaconing.

How to filter

1. Raise the RSSI threshold (e.g. -85 instead of -90) to ignore weaker interferers.
2. Listen: a real beacon repeats a fixed Morse pattern; an interferer’s bursts are irregular.
3. Scan multiple passes; a real beacon appears on every pass at the same frequency, an interferer appears sporadically.
4. Move the receiver; interference is usually local.

When interference is not the cause

If a hit appears only once in twenty passes and never again, it was noise. If it appears every pass at the same frequency with stable RSSI, it is a real transmitter - likely your own beacon or a neighbor’s.

Reducing local noise

• Keep the beacon away from USB chargers and switching supplies during SEARCH.
• The ESP32’s own WiFi/BT are off during SEARCH, so they are not the cause.
• The SX1262’s receive bandwidth is narrow (CW/FSK), which rejects most broadband noise naturally.

The honest view

In a quiet mountain valley, false hits are rare. In a campsite or near houses, expect some. Treat every hit as “check it” rather than “it is them”.