Most common causes
- Switching regulator noise couples into RF path.
- Poor grounding creates return current problems.
- Long unshielded wires act as antennas.
- Digital clocks or displays create interference.
- Receiver front-end is overloaded by nearby transmitters.
How to test
Start with antenna placement, cable loss, power supply noise and final enclosure testing. Then compare RSSI, SNR, packet loss or return loss before and after each change.
What to verify
Check antenna frequency, matching network, connector type, ground plane, cable routing, supply ripple and nearby sources of interference.