Troubleshooting field guide

Goal

By now you can find a frequency, pick a modulation, decode a protocol, replay to your own gear, and handle raw and rolling signals. This module is a repair manual. When something refuses to work, you should be able to name the failure, run a short checklist, and know within a minute or two whether you have a fixable mistake or a signal behaving exactly as designed.

Six problems catch beginners over and over: nothing decodes in Read, the Frequency Analyzer stays blank, a capture replays but does nothing, a replay that works once then stops, terrible transmit range, and a .sub file that won't load. Each one below is written as problem → likely causes → fixes.

How to diagnose: change one thing at a time

The fastest way to stay confused is to change three settings at once. The fastest way to a fix is boring and disciplined:

1. Confirm the signal exists. Before fighting with decoding, open Sub-GHz → Frequency Analyzer, hold the remote a few centimetres away, and press. A frequency means there's a signal to work with; nothing means the problem is upstream of decoding.
2. Change one variable, then re-test. Frequency, then modulation, then distance, then battery — one at a time, noting what you changed.
3. Separate "can't hear it" from "can't name it". Read failing tells you nothing alone. Read RAW records the pulses whether or not the Flipper knows the protocol, so it's your ground truth: if RAW captures and Read doesn't, the signal is fine and the protocol is just unknown.
4. Write down what fixed it. The same remotes will misbehave again next month. A one-line note ("garage remote: it was on 310.0, not 315") saves the hunt twice.

Keep the three Sub-GHz tools straight in your head, because most of troubleshooting is picking the right one:

Problem: nothing decodes in Read

You open Sub-GHz → Read, press the remote, and the screen just sits there. This is the single most common beginner report, and it has six usual causes. Walk them in order — the flowchart below is the same order, top to bottom.

1 · Wrong frequency

Read only listens on one frequency at a time. If you left it on 433.92 MHz and your remote is a North-American keyfob on 315 MHz, you will hear silence. The fix is to stop guessing: use Sub-GHz → Frequency Analyzer to read the actual frequency off the remote, then set Read to that. The four numbers you will meet most are 315, 433.92, 868 and 915 MHz.

2 · Wrong modulation

Even on the right frequency, Read has to be on the right modulation preset or the pulses look like noise. Sweep the four stock presets deliberately: AM650 AM270 FM238 FM476. Most cheap OOK remotes (garages, barriers, plug sockets) land on AM650; narrower or noisier ones want AM270; FSK devices want one of the FM presets. Change the preset in Read's configuration, re-press the remote, repeat.

3 · Too far, or too weak

Sub-GHz receiving falls off fast with distance and through walls. A remote pressed across the room, or a low-power sensor, may not reach the Flipper's small internal antenna. Hold the remote within a few centimetres, point it at the top of the Flipper, and press firmly. A dying battery in the remote also weakens its signal — swap it if you can.

4 · It's a protocol the Flipper can't decode

Read only prints a name, bit count and key for protocols it recognises, and plenty of real devices use variants it has never been taught. That's not a failure of the capture — it's a gap in the decoder. Switch to Sub-GHz → Read RAW, which records the pulse timings regardless. If RAW captures a clean burst on every press, the signal is fine and you simply have an unnamed protocol. (You can still replay a RAW capture of a fixed-code device — see Module 5.)

5 · It's rolling, and that's not a bug

If Read does decode it — say Nice FloR-S or a KeeLoq-based protocol — but a Cnt (counter) value climbs by one every press, you're looking at a rolling code. It decoded perfectly; it just won't replay, because the counter makes every press different. See Module 5 for the full story — the short version is "the security feature doing its job."

6 · A noisy band

Some frequencies, 433.92 MHz especially, are crowded — weather stations, tyre sensors and other remotes all chatter there. If Read keeps triggering on junk or the analyzer keeps jumping, move away from other electronics, or capture the exact instant you press with Read RAW so you can pick your burst out of the noise later.

Not sure which of the three tools to pick for a given situation? Poke at this — describe the symptom and it points you at Read, Read RAW or the Frequency Analyzer:

Problem: Frequency Analyzer shows nothing, or jumps around

The Frequency Analyzer is your "is there even a signal?" tool. When it misbehaves, it is usually one of these:

If your device really does sit on an odd frequency outside the analyzer's default list, that's exactly what Momentum's extended-frequency options are for — see Module 8.

Problem: you captured it, but replay does nothing (or works once)

These two symptoms feel the same in the moment but have completely different causes, so keep them separate.

Replay works once, then stops

This is the classic. You save a gate or garage remote, it works the first time, and after that the real remote works but yours doesn't. That's a rolling code — the single most important thing to recognise on this whole course.

Rolling-code remotes (families like Nice FloR-S, KeeLoq, and Chamberlain/LiftMaster's Security+ 2.0) include a counter that increases every press. The receiver remembers roughly where the counter should be and rejects any code that isn't ahead of what it has already seen. Your replay sends an old counter value the receiver has already burned, so it's ignored. You can spot these on the Read screen before you even try: they decode fine but show a Cnt that climbs by one each press.

Replay does nothing at all — even on a fixed-code device you own

If you're sure it's a simple fixed-code device (it decodes with a stable key and no climbing counter) and replay still does nothing, work this checklist:

1. Weak transmit or range. The Flipper's internal antenna is modest. Get close to your receiver and try again before assuming the capture is bad.
2. Wrong device, or too far. Double-check you're aiming at the right receiver and that it's actually powered and in range.
3. Partial or noisy capture. If you recorded with Read RAW in a crowded band, you may have grabbed only part of the burst or mixed in noise. Re-record cleanly, close to the remote, pressing once and deliberately.
4. The device expects several presses. Some receivers only act after two or three repeats, or a press-and-hold. Send the capture a few times, or hold as your real remote would.
5. It was rolling after all. If it worked exactly once and never again, go back up a section — that's a counter, not a range problem.

Problem: terrible range on transmit

Your capture is good and your device is fixed-code, but you have to be almost touching the receiver for it to react. Sub-GHz range on a stock Flipper is genuinely limited, and several things stack up:

antenna

The Flipper has a small internal PCB antenna tuned to work broadly, not brilliantly. It is a compromise across a huge band, so no single frequency is optimal.

orientation

Antennas are directional. Try holding the Flipper flat, then upright; keep it roughly parallel to the receiver's antenna. Small changes in angle can matter more than distance.

obstacles

Walls, metal, and especially a car body soak up Sub-GHz energy. Line of sight helps enormously. A gate motor inside a metal box is a worst case.

battery

A low Flipper battery can reduce transmit power. Charge it before you blame the capture.

external module

A proper external CC1101 radio module with a real whip antenna is the biggest single upgrade for range. That's covered in Module 8.

The physics explains the compromise: wavelength is λ = c / f, so 433.92 MHz has a wavelength of about 69 cm and an ideal quarter-wave antenna of roughly 17 cm — too big for a pocket. The internal antenna trades length for portability; an external module lets you fit an antenna closer to that ideal.

Problem: the .sub won't load, or the SD card acts up

Sub-GHz captures live as .sub text files on the microSD card, and RFID and NFC files live there too. When files vanish, won't open, or the Flipper complains about storage, the cause is almost always the card itself, not your capture. Keep this generic and low-drama:

1. Re-seat the card. Power down, remove the microSD, blow out any dust, push it back until it clicks, and boot again. A card that's a hair loose looks exactly like a dead card.
2. Check the format. The Flipper expects the card formatted as FAT32. A card that came as exFAT, or one that got corrupted, can fail to mount. Back up anything you care about, then reformat to FAT32 (on a computer, or with the Flipper's own storage tools).
3. Sanity-check the filename. Keep names simple: letters, numbers, dashes, and the .sub extension. Odd characters or a wrong extension can make a file refuse to open. If you edited a capture on a computer, make sure you didn't save it as .sub.txt.
4. Look at the file's insides. A valid Sub-GHz key file starts with lines like Filetype: Flipper SubGhz Key File, Version: 1, a Frequency:, a Preset:, and either protocol fields or a RAW_Data: block. If those top lines are missing or mangled, the file is the problem, not the reader.
5. Try a known-good card. If nothing loads and even fresh captures won't save, the card may be failing. A different, decent-quality microSD is a cheap test.

Filetype: Flipper SubGhz Key File
Version: 1
Frequency: 433920000
Preset: FuriHalSubGhzPresetOok650Async
Protocol: Princeton
Bit: 24
Key: 00 00 00 00 00 8C 5A 3B
TE: 400

Lab

Field notes: the one-glance table

Tape this to the inside of your skull. When something breaks, start at the symptom and read across.

Check yourself

Verify the details

Read the primary sources: Flipper: reading signals and presets · Flipper: demodulated RAW recordings. Course review: 10 September 2026.