BPQ / LinBPQ setup

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.

WARNING

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

Prepare the TNC

Open a serial monitor at 115 200 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:

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

Expected stats timing:

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

Serial device

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

Prefer /dev/serial/by-id/... over /dev/ttyUSB0 for a stable path after reboot. Use that path as COMPORT in bpq32.cfg.

Recommended BPQ port settings

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

• TXDELAY=0 — avoids a long wait before BPQ transmits.
• PERSIST=255 — allows immediate transmit when the TNC queue is ready.
• FULLDUP=0 — keeps the link half-duplex, important for LoRa.
• MAXFRAME=1 — 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.
• NOKEEPALIVES=1 — reduces unnecessary KISS chatter.

Complete bpq32.cfg

A complete example is in examples/bpq32-axloratnc.cfg. Copy it and edit:

NODECALL   NODEALIAS   LOCATOR   COMPORT
IDMSG / BTEXT / INFOMSG / CTEXT

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

Restart LinBPQ after editing.

Basic test

From another AX.25 / BPQ node:

C YOURCALL-7

Useful diagnostics on the AXLoRaTNC console:

console
stats
radio
mheard
mode kiss

Watch these counters: txq queued deferred qdrops raw_tx raw_rx duty_drops.

If deferred grows quickly, CSMA or duty-cycle is holding back frames. For the fast lab profile, duty_drops should stay at zero.

Extending range / robustness

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

radio bw 62.5
radio sf 8
radio cr 8

Adjust BPQ to be more patient:

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