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AXLoRaTNC with LinBPQ / BPQ32

This guide documents the working BPQ setup for AXLoRaTNC in KISS mode.

AXLoRaTNC behaves like a serial KISS TNC. BPQ sends complete AX.25 frames to the ESP32 over USB serial. AXLoRaTNC adds the AX.25 FCS, sends one complete AX.25 frame per LoRa packet, receives LoRa packets, checks FCS, and returns KISS frames to BPQ.

Tested Fast Setup

Use the same RF settings on every AXLoRaTNC node:

Frequency: 869.480 MHz
Bandwidth: 125 kHz
SF:        7
CR:        4/5
KISS baud: 115200

For bench/lab testing, the fastest working TNC profile is:

radio reset
profile fast
mode kiss

profile fast sets:

txdelay=0
persistence=255
slot=1
fulldup=0
duty=off

Important: profile fast disables the firmware duty-cycle guard. Use it only on a dummy load or shielded lab setup. For normal RF operation, enable a legal duty-cycle setting again.

Prepare The TNC

Open a PlatformIO monitor or serial terminal at 115200 baud:

./venv/bin/pio device monitor -b 115200

Configure the node:

mode console
callsign YOURCALL-0
radio reset
profile fast
radio
stats
mode kiss

Expected radio output should show roughly:

freq=869.480 bw=125.0 sf=7 cr=4/5

Expected stats timing should show:

kiss_txdelay=0 p=255 slot=1 fulldup=0

In KISS mode, type plain text console followed by Enter to return to the local console.

Serial Device

Find the ESP32 serial port:

ls -l /dev/serial/by-id/

Prefer /dev/serial/by-id/... over /dev/ttyUSB0, because it stays stable after reboot. Use that path as COMPORT in bpq32.cfg.

Recommended BPQ Port Settings

These settings are the important part:

TYPE=ASYNC
PROTOCOL=KISS
SPEED=115200
FULLDUP=0
TXDELAY=0
PERSIST=255
SLOTTIME=10
TXTAIL=0
MAXFRAME=1
PACLEN=80
FRACK=8000
RESPTIME=1000
RETRIES=10
NOKEEPALIVES=1

Notes:

  • TXDELAY=0 avoids the long wait before BPQ transmits.
  • PERSIST=255 allows immediate transmit when the TNC queue is ready.
  • SLOTTIME=10 is fast enough for local LoRa bench testing.
  • FULLDUP=0 keeps the link half-duplex, which is important for LoRa.
  • MAXFRAME=1 is more reliable on LoRa. Try MAXFRAME=2 only after the link is stable.
  • PACLEN=80 keeps LoRa airtime short. Increase slowly if RSSI/SNR are strong and retries stay low.
  • NOKEEPALIVES=1 reduces unnecessary KISS chatter.

Complete bpq32.cfg

A complete example is provided in:

examples/bpq32-axloratnc.cfg

Copy it to your BPQ config location and edit:

NODECALL
NODEALIAS
LOCATOR
COMPORT
IDMSG / BTEXT / INFOMSG / CTEXT

Example install path:

sudo cp examples/bpq32-axloratnc.cfg /opt/linbpq/bpq32.cfg

Restart LinBPQ after editing.

Basic Test

Start BPQ, then from another AX.25/BPQ node connect to the BPQ node call:

C YOURCALL-7

On AXLoRaTNC console, useful diagnostics are:

console
stats
radio
mheard
mode kiss

Watch these counters:

txq
queued
deferred
qdrops
raw_tx
raw_rx
duty_drops

If deferred grows quickly, BPQ or the TNC is waiting because of CSMA or duty-cycle. For the fast lab profile, duty_drops should stay at zero.

If raw_rx increases but BPQ does not see frames, check:

mode kiss
SPEED=115200
COMPORT=...

If raw_tx increases but the other node hears nothing, check both nodes have the same:

freq
bw
sf
cr
sync word

More Range / More Robustness

For longer range, use slower LoRa settings on every node:

radio bw 62.5
radio sf 8
radio cr 8

Then adjust BPQ to be more patient:

MAXFRAME=1
PACLEN=60
FRACK=12000
RESPTIME=1500
RETRIES=15

This costs speed but improves weak-link behavior.