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SDRLAB Troubleshooting Hub

The golden rule: always debug in this order — hardware first, then driver, then settings. Ninety percent of SDR problems are an unplugged antenna, an old driver, or a wrong setting hiding in plain sight.

Problem index​

CategoryProblems covered here
RTL-SDR V4Not detected ・ Strange signals / aliasing ・ Bias tee not working
TRX-duoWeb UI unreachable ・ Boot loop / no DHCP ・ No receive signal
H4MApps missing after update ・ Does not power on ・ No audio
Flipper modulesModule app says "no module" ・ NRF24 sees nothing ・ WiFi board won't connect ・ Ethernet module no link

RTL-SDR not detected​

Symptom​

rtl_test prints No devices found. or GQRX lists no devices.

Diagnosis​

lsusb

Expected output shows the dongle:

Bus 001 Device 004: ID 0bda:2838 Realtek Semiconductor Corp. RTL2838 DVB-T

If lsusb shows nothing, the USB connection itself is the problem (cable, port, hub). If it does show the device, continue.

Root cause​

The kernel's DVB-T driver (dvb_usb_rtl28xxu) grabbed the dongle before the SDR driver could — the classic RTL-SDR failure mode.

Fix​

  1. Blacklist the DVB driver:
echo 'blacklist dvb_usb_rtl28xxu' | sudo tee /etc/modprobe.d/blacklist-dvb_usb_rtl28xxu.conf
  1. Reboot, or sudo modprobe -r dvb_usb_rtl28xxu if the module is loaded.
  2. Re-run rtl_test — expect Found 1 device(s).
  3. Still nothing? Install the current driver from source — see RTL-SDR V4 → Linux install.

RTL-SDR picks up images of other signals​

Symptom​

You tune to one frequency but hear stations from other frequencies mixed in, especially on HF.

Root cause​

Overload from strong broadcast stations, or tuning below ~24 MHz where old-style dongles fold signals (aliasing). The RTL-SDR Blog V4 handles this differently from older dongles — it has a built-in 28.8 MHz upconverter for HF and a triplexer + notch filters for strong FM/DAB interference.

Fix​

  • On HF, make sure your driver supports the V4 (R828D). With an outdated driver the upconverter isn't activated and HF behaves like an aliasing mess.
  • Turn the gain down (start at 20–30 dB) — most "ghost signals" are overload.
  • Add attenuation or use a band-specific antenna instead of a wideband one.

Bias tee won't turn on​

Symptom​

An active antenna that needs DC power doesn't get it.

Root cause​

The V4 bias tee is software-controlled (4.5 V, 180 mA). In SDR# / SDR++ it is mapped to the "Offset tuning" option; it must be enabled per session.

Fix​

Enable "Offset tuning" in the device config (this is the bias-tee switch on V4). In GQRX, click the device icon → enable Bias-T. Note the tee can't supply heavy loads — 180 mA max.

TRX-duo web UI unreachable​

Symptom​

Browser won't load the TRX-duo dashboard; ping fails.

Diagnosis​

ip neigh show
arp -a

Look for an address like 192.168.1.100 or a trx-duo-alpine hostname.

Root cause​

Network misconfiguration: the device expects DHCP, or you are on a subnet where its default static address doesn't fit.

Fix​

  1. Connect the TRX-duo to the same switch/router as your PC.
  2. Prefer a network with DHCP — the device requests an address automatically.
  3. If no DHCP server exists, the Red Pitaya-compatible default is http://192.168.1.100 — set your PC to a static 192.168.1.x address and try that.
  4. See TRX-duo → First boot and network for the full official procedure.

TRX-duo boots but never appears on the network​

Symptom​

Power LED on, but no link light on the Ethernet jack, or link light on but no address.

Diagnosis​

  • Check the Ethernet link LED on the RJ45 jack — if it's dark, the cable/port is the problem.
  • Check the SD card: a corrupted or wrong image means the OS never boots far enough to configure networking.

Root cause​

Usually one of: bad cable, card not fully seated, or an image written for the wrong board variant.

Fix​

  1. Try another cable/port.
  2. Re-seat and re-write the microSD card with the official image (see Firmware and SD image).
  3. If it still won't appear, test the card on a PC — a card that fails fsck or reads as near-empty is suspect.

TRX-duo RX shows noise only​

Symptom​

The waterfall is alive but you hear nothing, even on strong HF broadcasters.

Diagnosis​

Check the input: is the antenna on the RX1/RX2 SMA port? Is it the correct band (10 kHz – 60 MHz)?

Root cause​

No antenna / wrong port, input attenuator engaged, or a receive app with gain set to minimum.

Fix​

  1. Attach a proper HF antenna (a long wire or a tuned loop — a 2.4 GHz WiFi antenna is nearly useless here).
  2. In the app, raise the RX gain / disable attenuators.
  3. Confirm the app you launched is an SDR receiver app, not the VNA.

H4M apps missing after firmware update​

Symptom​

The PortaPack boots, menus look right, but many apps are gone.

Root cause​

Since Mayhem 1.8.0, most applications live on the microSD card, not in flash. A missing or out-of-date SD card means missing apps.

Fix​

  1. Get a microSD card (16 GB is comfortable), format it FAT32.
  2. Download the release's COPY_TO_SDCARD archive from the Mayhem releases page — see H4M → Mayhem firmware.
  3. Extract the archive to the card root.
  4. Insert and reboot. Apps appear.

H4M won't power on​

Symptom​

No display, no LEDs.

Diagnosis​

  • Charge via USB-C for 10+ minutes, then try the power switch (the H4M has a proper on/off button).
  • Try booting with the USB-C cable connected to a PC.

Root cause​

Flat battery is the usual suspect; occasionally a stuck DFU/flash mode.

Fix​

  1. Charge until the charging indicator shows progress.
  2. Hold the power button ~3 seconds.
  3. If it still won't start, connect USB-C and check if the PC sees a HackRF device — if yes, flash Mayhem again per H4M → Mayhem firmware.

H4M no audio from speaker or jack​

Symptom​

Signal in the waterfall, silence in the ear.

Root cause​

Mode/gain settings, or audio routed to the wrong output (the H4M auto-switches between the built-in speaker and the 3.5 mm jack when headphones are plugged in).

Fix​

  1. Raise the RX gain and re-check the demod mode (WFM for broadcast FM).
  2. Unplug headphones to re-route audio to the speaker, or vice versa.
  3. Check the volume setting in the audio menu.

Flipper app says "no module"​

Symptom​

An expansion app (NRF24, Marauder, GPS) reports the module isn't present even though it's plugged in.

Root cause​

The GPIO pins are not set for the module, or the Flipper firmware doesn't bundle the app. Most modules need a custom firmware (Momentum / Unleashed / Xtreme) and an explicit pin assignment.

Fix​

  1. On Momentum: Protocol Settings → GPIO Pin Settings — set the module's pins (exact pins per product page).
  2. On Unleashed/Xtreme: the equivalent GPIO config lives in the app's own settings or firmware settings.
  3. Reboot the Flipper and retry.

See the specific module pages: 5G board, NRF24, WiFi multiboard, Ethernet.

NRF24 sees nothing on channel scan​

Symptom​

The sniffer shows zero activity even with a wireless mouse/keyboard nearby.

Diagnosis​

Confirm the module's SMA antenna is attached and the mouse is actively moving (idle mice transmit little).

Root cause​

No antenna, wrong SPI pins, or simply no traffic: many 2.4 GHz devices use frequency hopping and are quiet when idle.

Fix​

  1. Attach the antenna.
  2. Verify pins per the NRF24 page.
  3. Move/jiggle the mouse or keyboard while scanning — you should see channel bursts.
  4. Try channel range 1–126 at 2 Mbps, then 1 Mbps and 250 kbps (different devices use different rates).

WiFi board web interface unreachable​

Symptom​

After flashing the deauther, you can't reach 192.168.4.1.

Root cause​

Your phone/PC auto-joined another network, or the board's AP didn't start.

Fix​

  1. Connect to the board's access point (default SSID pwned, password deauther).
  2. Disable mobile data / auto-join on the client.
  3. Browse to http://192.168.4.1.
  4. Still nothing? Re-flash the firmware per the WiFi multiboard page.

Symptom​

The RJ45 port LEDs stay dark after plugging in a cable.

Diagnosis​

  • Try another cable and another switch port (the module is 10/100 — some 1G-only "smart" ports are picky).
  • Confirm wiring to the Flipper per the Ethernet module page.

Root cause​

Bad cable/port, or the SPI wiring (CS/RESET) is wrong so the W5500 never initializes.

Fix​

  1. Test the cable with any known-good device first.
  2. Double-check every SPI wire — one swapped wire kills the link.
  3. Launch the app; the header should show LAN [UP 100M FD] when connected.

Still stuck?​

When bringing a problem to us (or a forum), include:

  • Device + firmware version: e.g. "RTL-SDR V4, osmocom driver 2.x"; "H4M, Mayhem nightly 2026-07-26"; "Flipper Zero, Momentum 8.x".
  • Environment: OS and version, USB hub or direct, network topology for networked devices.
  • Evidence: lsusb / dmesg output, rtl_test errors, hackrf_info output, screenshots of the app.
  • What you already tried: this prevents duplicate advice and shows the debug order was followed.

Related: Quickstart ・ Firmware & drivers ・ SDR software.