[Bug]: RAK6421+RAK13302: 30 dBm txPower request resolves to low Tx gain index (femLnaMode correctly enabled, GPIO confirmed high)

[amarand]

Category

Hardware Compatibility

Hardware

Linux Native, Other

Is this bug report about any UI (https://meshtastic.org/docs/configuration/device-uis/) component firmware?

• Meshtastic UI aka MUI
• InkHUD
• BaseUI

Firmware Version

2.7.26.54e0d8d

Description

Body

Hardware: RAK8623 WisMesh Station HP (RAK6421 HAT + RAK13302 1W module)
meshtasticd: 2.7.26.61-obs54e0d8d-beta (OBS beta channel)
OS: Raspberry Pi OS Trixie 64-bit, custom image, RPi 4

Summary

Requesting max txPower (30 dBm, US915) results in meshtasticd logging Requested Tx power: 30 dBm; Device LoRa Tx gain: 8 dB. The active config.d file's TX_GAIN_LORA table is:

[9, 9, 10, 11, 9, 8, 9, 10, 10, 10, 11, 12, 12, 12, 12, 12, 12, 12, 12, 10, 9, 8]

Gain value 8 sits near the bottom of this table (table peaks at 12, indices 11–18). A max-power request landing on a near-minimum gain value suggests a mapping/index bug between requested dBm and the corresponding TX_GAIN_LORA slot.

Ruled out

• HAT EEPROM detection: confirmed via /proc/device-tree/hat/product → 6421 Pi Hat
• config.d loading: confirmed via journalctl, file active at startup
• GPIO enable state: Enable_Pins [12, 13] confirmed out hi continuously via /sys/kernel/debug/gpio while daemon runs normally — PA enable is not the issue

Real-world symptom

Node is reliably outbeaten in range by a cheap SX1262-only tracker (no PA) on the same network, consistent with the 1W unit transmitting at bare-chip ceiling power rather than boosted output.

Config file

lora-RAK6421-13302-slot1.yaml, official RAK-shipped file bundled in meshtasticd package, unmodified.

Question

Is the 8 dB gain value correct for a 30 dBm request given this table, or is there an off-by-N indexing issue between requested power and the TX_GAIN_LORA array?

Cross-reference

Related RAK forum thread: https://forum.rakwireless.com/t/rak8623-wismesh-station-hp-rak13302-pa-not-engaging-at-full-1w-on-meshtasticd-2-7-15/17250

Relevant log output

INFO  | 10:13:17 0 Requested Tx power: 30 dBm; Device LoRa Tx gain: 8 dB
INFO  | 10:13:17 0 Set RX gain to boosted mode; result: 0
INFO  | 10:13:17 0 Applied SX1262 register 0x8B5 patch for RX improvement

[github-actions]

@amarand, Welcome to Meshtastic! 👋

Thanks for opening your first issue. If it's helpful, an easy way
to get logs is the "Open Serial Monitor" button on the Web Flasher.

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in the discussions tab
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Welcome to the community! ❤️

[jp-bennett]

The LoRa chip itself is set to 22 dB. At 22 dBm (the 22nd value on table) the TX gain is 8 dB. 22 + 8 is the 30 you requested.

This doesn't mean that there isn't another problem, but the numbers reported are expected.