Most common causes
- Wrong ESP32 module variant for external antenna.
- Poor antenna clearance on PCB.
- External antenna cable or U.FL connector is damaged.
- Board is mounted close to metal or large battery.
- Power supply noise affects RF performance.
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.