Troubleshooting

No Position Fix

A cold start under open sky takes 26 seconds. A hot start (ephemeris still cached from recent use) takes about 1 second. If neither is happening, work through these checks.

1. Verify antenna connection

   The L1/L5 antenna plugs into the IPEX socket on the HAT. It should click firmly into place. A loose connection kills signal reception entirely.

2. Check sky visibility

   GNSS signals do not penetrate buildings, metal roofs, or dense tree canopy. The antenna needs a direct line of sight to the sky. L5 signals are more sensitive to obstructions than L1.

   # Check how many satellites the module can see
   lc29h satellites

   You need at least 4 satellites for a 3D fix. Fewer than that means obstructed sky or antenna problem.

3. Watch the PPS LED

   When the PPS LED blinks once per second, the module has a fix. No blink means no fix.

4. Try a cold restart

   If the module has stale ephemeris data (moved a long distance while powered off, or battery died), a cold restart forces it to reacquire from scratch:

   lc29h restart cold

   This resets to a 26-second TTFF under open sky.

5. Check module orientation

   The module label should face downward (toward ground) with the antenna facing sky. Upside-down mounting inverts the antenna pattern.

Tip

If you just need to confirm the module is alive, run lc29h info first. If that returns firmware version and variant info, the serial link is working and the problem is RF/antenna related.

Caution

L5 signals require clearer sky than L1. If you are getting an L1-only fix but no L5 satellites, move the antenna to a more open location. Urban canyons and balconies with partial sky view often block L5 while L1 still works.

Serial Port Issues

Permission Denied

PermissionError: [Errno 13] Permission denied: '/dev/ttyS0'

Add your user to the dialout group:

sudo usermod -aG dialout $USER

Then log out and back in (or reboot). The group change does not take effect in your current session.

Wrong Device Path

Pi 4B

Connection	Device
GPIO UART (jumper B)	/dev/ttyS0
USB (jumper A)	/dev/ttyUSB0

Pi 5

Connection	Device
GPIO UART (jumper B)	/dev/ttyAMA0
USB (jumper A)	/dev/ttyUSB0

Other Linux

Connection	Device
USB (CP210x)	/dev/ttyUSB0 or /dev/ttyACM0

Check dmesg | tail after plugging in to see which device was assigned.

Baud Rate Mismatch

The factory default baud rate is 115200 for GPIO UART and 460800 for USB. If you get no response at 115200, try:

# Try factory default
lc29h --port /dev/ttyS0 --baud 9600 info

# Try USB default
lc29h --port /dev/ttyUSB0 --baud 460800 info

If the baud rate was previously changed and you don’t know the current value, you need to try common rates until one responds: 9600, 38400, 57600, 115200, 230400, 460800.

Caution

The Waveshare sample code sets the baud rate to 115200 on first run. If you have previously run the demo scripts, the module may no longer be at 9600 even if the datasheet says that is the factory default.

UART Not Enabled on Pi

If /dev/ttyS0 (Pi 4B) or /dev/ttyAMA0 (Pi 5) does not exist:

1. Enable serial port

   sudo raspi-config
   # Interface Options -> Serial Port -> Yes

2. Add UART overlay (if raspi-config alone does not create the device)

   Add to /boot/firmware/config.txt (Pi 5) or /boot/config.txt (Pi 4B):

   dtoverlay=uart0

3. Reboot

   sudo reboot

No Data at All

If the device exists but you get zero output:

• Verify the yellow jumper matches your connection method (B = UART, A = USB)

• Check that the antenna is connected (module may not output NMEA without a satellite search in progress on some firmware versions)

• Try reading raw serial data to rule out CLI issues:

  # Read raw bytes from the port (Ctrl+C to stop)
  stty -F /dev/ttyS0 115200 raw -echo
  cat /dev/ttyS0

  If you see NMEA sentences here but lc29h does not work, the issue is in the CLI configuration, not the hardware.

NTRIP Connection Failures

rtk2go.com Rejects Connection

Caution

rtk2go.com requires a valid email address as the username. An arbitrary string like “user” or “admin” will be silently rejected. Use the email you registered with.

lc29h ntrip start \
  --host rtk2go.com \
  --port 2101 \
  --mount YOUR_MOUNT \
  --user your@email.com \
  --password none

Mount Point Not Found

The mount point name is case-sensitive and must exist on the caster. Browse available mount points:

# List all mount points from a caster
lc29h ntrip sources --host rtk2go.com --port 2101

Or check the web status page: rtk2go.com:2101/SNIP::STATUS

Connection Timeout

Common causes:

Symptom	Likely Cause	Fix
Connection refused	Wrong port	Standard NTRIP port is 2101
Timeout after 10s	Firewall blocking outbound TCP	Open port 2101 outbound
DNS resolution failure	No internet	Check ping rtk2go.com
Intermittent drops	Unstable network	Use wired ethernet instead of WiFi

Base Station Too Far Away

NTRIP corrections degrade with distance. As a rule of thumb:

Baseline Distance	Expected Accuracy
< 10 km	1—2 cm (RTK Fixed typical)
10—30 km	2—5 cm (RTK Fixed possible)
30—50 km	Float only in many cases
> 50 km	Corrections effectively useless

Use lc29h ntrip sources to find the closest mount point to your location. If nothing is within 30 km, consider setting up your own base station with the LC29H(BS).

RTK Not Getting Fix

Float vs. Fixed

RTK Float (GGA quality 5) means the module is receiving and applying corrections, but has not resolved the carrier-phase integer ambiguities. This gives decimeter accuracy (~20 cm) rather than centimeter.

RTK Fixed (GGA quality 4) means full ambiguity resolution — centimeter accuracy.

The typical progression after starting corrections:

No Fix (0) -> Autonomous (1) -> RTK Float (5) -> RTK Fixed (4)

If you are stuck at Float:

1. Check baseline distance — move to a closer mount point if possible (see table above)

2. Verify constellation overlap — the base and rover must track the same satellites. A single-band (L1-only) base station paired with the LC29H’s dual-band receiver will still work, but convergence is slower.

3. Confirm RTCM message types — for full dual-band RTK, the base should send:

   Message	Content
   1005	Station coordinates (antenna reference point)
   1077	GPS MSM7 (full observables)
   1087	GLONASS MSM7
   1097	Galileo MSM7
   1127	BeiDou MSM7

   Missing messages reduce the number of satellites used for ambiguity resolution.

4. Wait longer — in marginal conditions (long baseline, partial sky), convergence from Float to Fixed can take 5+ minutes. Do not move the antenna during initial convergence.

5. Check antenna quality — multipath from nearby buildings, metal surfaces, or the ground degrades carrier-phase measurements. Raise the antenna above obstructions.

Tip

MSM7 messages contain full carrier-phase and pseudorange observables. MSM4 is a lighter alternative with slightly less data. If your base only sends MSM4, convergence will be slower but still possible.

Frequent Fix Drops

If the fix oscillates between Fixed and Float:

• Multipath — metal roofs, glass buildings, and vehicles near the antenna cause carrier-phase cycle slips. Move the antenna to a clearer location.
• Baud rate too low — RTCM3 data at 1 Hz with MSM7 for 4 constellations is roughly 2—3 KB/s. At 9600 baud (~960 bytes/s), the serial link cannot keep up. Use 115200 or higher.
• Correction stream interruptions — check your internet connection stability. A 10-second gap in RTCM data can cause the module to drop from Fixed back to Float.

Pi 5 Specific Issues

Different UART Device Path

The Pi 5 uses /dev/ttyAMA0 for GPIO serial, not /dev/ttyS0 like the Pi 4B. This is because the Pi 5 uses the PL011 UART peripheral rather than the mini UART.

# Pi 4B
lc29h --port /dev/ttyS0 info

# Pi 5
lc29h --port /dev/ttyAMA0 info

Bluetooth Conflict

On both Pi 4B and Pi 5, Bluetooth uses the PL011 UART by default, which can conflict with GPIO serial. If you see garbled data or intermittent communication failures:

Disable Bluetooth

Add to /boot/firmware/config.txt (Pi 5) or /boot/config.txt (Pi 4B):

dtoverlay=disable-bt

This frees the PL011 UART entirely for the LC29H.

Move Bluetooth to Mini UART

If you need Bluetooth, move it to the mini UART instead:

dtoverlay=miniuart-bt

This gives the LC29H the full PL011 UART while Bluetooth runs on the less capable mini UART.

Reboot after changing config.txt.

Caution

The Pi 5 GPIO pinout is physically identical to the Pi 4B — the HAT mounts the same way. But the underlying UART peripheral changed, so the device path and Bluetooth interaction are different. Code and scripts that hardcode /dev/ttyS0 will break on Pi 5.

Common Error Messages

$PAIR001,<cmd>,0*XX — Command Acknowledged

This is not an error. Result code 0 means success. The module accepted and executed the command.

$PAIR001,<cmd>,1*XX — Command Failed

The command was recognized but could not be executed. Common causes:

• Sending an RTK command to a non-RTK variant (e.g., PAIR432 to an LC29H(AA))
• Module is in a state that does not support the command

$PAIR001,<cmd>,2*XX — Not Supported

The command ID is not recognized by this firmware version or variant.

$PAIR001,<cmd>,3*XX — Invalid Parameter

A parameter is out of range. Check the PAIR Command Reference for valid ranges.

No Response At All

If you send a command and get nothing back:

1. Check baud rate — the module will not respond if you are transmitting at the wrong speed
2. Check wiring — TX from the host must connect to RX on the module, and vice versa
3. Verify command format — every command needs the $ prefix, * checksum delimiter, and correct two-character hex checksum followed by \r\n
4. Check for echo — if you see your own command echoed back, TX and RX may be swapped

PQTMSVINSTATUS Shows valid=0

During base station survey-in, the module reports status periodically. valid=0 means the survey has not yet converged to the configured accuracy threshold.

$PQTMSVINSTATUS,1,0,3600,542,2.3451*XX

Field	Meaning
1	Survey-in mode active
0	Not yet valid
3600	Target duration (seconds)
542	Elapsed time so far
2.3451	Current 3D accuracy estimate (meters)

This is normal — survey-in for a 1 m accuracy target typically takes the full configured duration. Wait for valid=1 before switching to fixed mode.

Tip

You can monitor survey-in progress in real time with: lc29h --port /dev/ttyS0 monitor. Watch for the accuracy value to decrease over time. If it plateaus well above your target, the antenna placement may have too much multipath.

Quick Diagnostic Checklist

If nothing else has worked, run through this sequence to isolate the problem layer by layer:

# 1. Does the serial device exist?
ls -la /dev/ttyS0    # or /dev/ttyAMA0 on Pi 5

# 2. Can we open the port?
lc29h --port /dev/ttyS0 info

# 3. Is the module producing NMEA data?
lc29h --port /dev/ttyS0 monitor

# 4. How many satellites are visible?
lc29h satellites

# 5. What is the current fix status?
lc29h --port /dev/ttyS0 monitor
# Look for "Fix: 3D" vs "Fix: No Fix"

If step 1 fails, the problem is OS/driver configuration. If step 2 fails, the problem is serial communication (baud rate, wiring, permissions). If step 3 shows data but no fix, the problem is antenna/sky view. If satellites are visible but fix quality is poor, the problem is environmental (multipath, obstructions) or configuration (wrong variant for your use case).