ESP32 + RFM95: What Voltage & Which Antenna?

Common Issues with Incorrect Power or Antenna Setup

When the RFM95/RFM96 is powered improperly or paired with a mismatched antenna, you may see:

• Brownouts or weak supply voltage → leads to dropped packets, reduced output power, or sudden module resets.

• Over-voltage stress (>3.9 V) → can permanently damage the RF front end.

• Under-powered regulator during TX → module fails to reach full +20 dBm, resulting in lower range.

• Improper or missing antenna → reflected power (high VSWR) causes poor RSSI and risks damaging the PA.

• Random SPI communication faults → especially when VCC noise couples into the SPI clock/data lines.

Good Practices for Powering the RFM95 with ESP32

• Stable 3.3 V Regulation
  Use a regulator capable of at least 500 mA headroom. The RFM95 itself can draw up to 120–150 mA at TX peak.

• Decoupling & Bulk Capacitors
  Place 100 nF + 10 µF ceramics at the VCC pins. A 47–100 µF electrolytic helps handle TX current spikes.

• Shared vs. Separate Rails
  If the ESP32 is pulling heavy current (Wi-Fi, BLE + LoRa), consider isolating the RFM95 with a dedicated low-noise LDO.

Choosing the Right Antenna

• Match Frequency to Module → e.g. 868 MHz, 915 MHz, or 433 MHz. Using the wrong band severely reduces range.

• Impedance Matching → Stick with 50 Ω antennas to avoid reflections and power loss.

• Form Factor → Whip antennas generally outperform PCB traces; SMA connectors are recommended for testing.

• Keep RF Path Clean → Short coax, no sharp bends, good ground plane for stability.

A Practical Alternative

If you want to avoid the trial-and-error of power supply design and antenna matching, consider a ready-made LoRa-enabled board. For example, the STMicroelectronics board integrates a sub-GHz transceiver with stable power management and optimized RF layout—helping you skip common hardware pitfalls while getting reliable long-range wireless right away.