RAK6421 + RAK13302 not outputting 1W

WisBlock
1

Please include the following information, in order for us to help you as effectively as possible.

  • What product do you wish to discuss? RAK6421 + RAK13302

  • Computer OS? (MacOS, Linux, Windows) Linux (Raspberry Pi)

  • What Computer OS version? Debian GNU/Linux 13.4 (trixie)

  • How often does the problem happen? consistently

  • How can we replicate the problem?

  1. Put the RAK13302 module on a RAK6421 pi hat, and set the jumper pins for the EXT option
  2. Connect the external battery connector to the RAK13302 and connect to a 5V 2.5A+ power supply (not turned on yet) and connect an antenna using a UFL to SMA or N cable adapter
  3. Image a microSD card with the raspian OS - Debian trixie 13.4 and put it in the raspberry Pi
  4. Put the 6421 on the raspberry Pi GPIO pins, connect the RPi to a video monitor and keyboard/mouse, and network cable connected to an internet router and turn on the power supply
  5. Set up the raspberry Pi with local settings (mine is US/english)
  6. Install the pyMC_repeater: GitHub - pyMC-dev/pyMC_Repeater: A lightweight Repeater Daemon implemented in Python, built using the pymc_core library. · GitHub
    follow instructions to enable SPI on the RPi and then git clone the code
    A) set it up for the RAK6421+1330x option
    B) use the US/Canada radio settings option
    c) Finish the configuration from the web interface http://[RPi IP address]:8000
  7. Look at the power consumption with the system idle
  8. Advert the repeater and look at the power consumption
    9.Under “Configuration”, “Radio configuration”, adjust the tx power and repeat - try using small increments from 18dbm to 30 dbm
  9. Check the current usage with an advert transmission after each adjustment

In my case, the power sits at ~290mA while idle, and only goes up to a max of around 400mA on transmit. This means the RAK board is only using ~110mA, which is way too low for having the power amplifier engage.

I have sufficient current available, so it isn’t a power supply issue.
I suspect either something is missing in the pyMC code to actually get the PA to engage, or there is an issue with my RAK13302

Please help me understand what the problem might be,
Thank you,

Brett-

2

Welcome to RAK forum @bps94945 ,

It seems that RAK6421 is supported. However, it is best to check with pyMC/MeshCore about this issue. There might be other settings needed to fully use the 1W module via its control pins.

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3

Hey Brett, I’m planning a similar build and ran into this thread while researching.

I was looking at the RAK13302 schematic and noticed there’s a pin called ANT_SW on pin 31 (IO3) that goes to PA_CSD on the SKY66122 — which I think is the chip shutdown pin for the power amplifier. On IO Slot 1 that maps to GPIO13.

I could be wrong, but it looks like that pin might need to be held high to actually wake up the PA. The current pyMC_Repeater profile for the RAK6421 doesn’t seem to include any enable pin, which might explain why the PA isn’t engaging and you’re only seeing the bare SX1262 output.

Not sure if that’s something that would go under rxen_pin or txen_pin in the config, or if there’s something else going on. Just thought it was worth mentioning in case it helps.

Did you ever get this sorted out?

4

Hardware:

  • Raspberry Pi 3B
  • RAK6421 WisBlock Pi HAT
  • RAK13302 (SX1262 + SKY66122 1W booster) in IO Slot 1
  • External 5V/2A power supply connected to RAK13302 Jx connector
  • 915MHz antenna

Software:

  • Debian GNU/Linux 13 (trixie), aarch64
  • meshtasticd 2.7.15

Problem:

The SKY66122 power amplifier does not appear to be engaging. A nearby node consistently reads RSSI -103 to -104dBm from my node regardless of configuration changes. At 2 feet distance with a 1W transmitter I would expect -20 to -40dBm.

What I’ve tried:

  1. Jumper on EX_5V position (right two pins) — RSSI got worse (-116dBm)
  2. Uncommented Ant_sw: 13 in the config — no improvement
  3. Added Enable_Pins: [12, 13] and TX_GAIN_LORA from the official lora-RAK6421-13302-slot1.yaml — RSSI got worse (-117dBm)
  4. Reverted to original config — back to -104dBm baseline

Current working config (lora-hat-rak-6421-pi-hat.yaml):

yaml

Lora:
  Module: sx1262
  IRQ: 22
  Reset: 16
  Busy: 24
  # Ant_sw: 13
  DIO3_TCXO_VOLTAGE: true
  DIO2_AS_RF_SWITCH: true
  spidev: spidev0.0

Question:

What is the correct configuration to actually engage the SKY66122 PA under meshtasticd on Linux? Is Enable_Pinssupported in meshtasticd 2.7.15, or is this a feature in a newer version? Does the jumper position matter when using meshtasticd vs the official RAK image?

5

I think I found a solution. Seems the Meshtastic implementation doesn’t hold the PA pins 12 and 13 high so you have to force them using a gpiochip0 daemon. RSSI jumped from -103dBm to -49dBm — (a 54dB improvement!) and SNR went from -2.75dB to +7.00dB!! Big improvement!

Here’s what I used that seems to do the trick:

sudo tee /etc/systemd/system/rak13302-enable.service << 'EOF'
[Unit]
Description=Enable RAK13302 PA pins
Before=meshtasticd.service

[Service]
Type=forking
ExecStart=/usr/bin/gpioset --daemonize --chip gpiochip0 12=1 13=1

[Install]
WantedBy=multi-user.target
EOF

sudo systemctl daemon-reload
sudo systemctl restart rak13302-enable.service
sudo systemctl status rak13302-enable.service

Check from another node and should see a good boost on the signal.