Find the frequency
"Frequency" sounds like physics homework. It's actually just a channel number — a place on the dial where a device shouts. This module turns it into a real number you read off your own remote in about ten seconds.
Goal
By the end of this module you will point a remote at your Flipper, read a number like 433.92 off the screen, and know what that number means. You'll also know why some remotes proudly announce their frequency and others show you a stubborn blank — and why the blank is often the most interesting result of all.
Everything downstream — capturing, decoding, replaying — starts by getting two dials right. This module is the first dial: where the signal lives. Module 2 is the second dial: how it's shaped. Nail the first one here.
Seeing a signal for what it is
A radio remote does not send words. It sends a carrier — a pure tone of radio energy at one specific frequency — and flicks that tone on and off in a pattern. Frequency is simply how fast that carrier wiggles, measured in cycles per second, or hertz (Hz).
The numbers get large fast, so we use prefixes: one kilohertz (kHz) is a thousand cycles per second, one megahertz (MHz) is a million, one gigahertz (GHz) is a billion. A garage remote at "433.92 MHz" is wiggling its carrier about 434 million times a second. You don't feel it, your radio does.
The clearest way to build intuition is to look at the air. The scope below is a stand-in for what a radio "sees": a flat baseline of background noise with occasional spikes where a signal appears. Drag the tuning and press the sample remotes — notice how a signal only shows up when you're tuned near where it actually lives.
Two words to keep from that scope:
- Noise floor
- The low, restless baseline that's always there — the electrical hum of the world. Real signals are the parts that rise clearly above it.
- Peak
- A spike above the floor. A strong, close, correctly-tuned transmitter makes a tall, obvious peak. A weak or mistuned one barely clears the noise.
This is the entire game of "finding a frequency": get tuned close enough that the device's peak stands up out of the floor so the Flipper can measure exactly where it is.
The four bands you'll actually meet
The Flipper's radio can tune a wide range, but consumer gear clusters tightly. In practice, four frequencies cover the overwhelming majority of remotes you'll ever hold:
| Frequency | Where it's common | Typical devices | Notes |
|---|---|---|---|
| 315 MHz | North America | Garage doors, older car fobs, TPMS | The classic US remote band |
| 433.92 MHz start here | Worldwide | Doorbells, LED remotes, weather stations, gates | The global workhorse — a license-free ISM band nearly everywhere |
| 868 MHz | Europe | Alarms, sensors, smart-home gear | The EU counterpart to 915 |
| 915 MHz | North America | Sensors, IoT, industrial remotes | A US/Americas ISM band |
Region matters. The same product sold in Denver and Düsseldorf may ship on different frequencies to fit local rules — a US doorbell on 315, its EU twin on 433.92 or 868. There is no universal "doorbell frequency"; there's only "what this device does," which is exactly why you measure instead of guess.
The clustering is a gift to a beginner. Because manufacturers crowd onto the same handful of free bands, your guesses have great odds and your search space is tiny. You are not hunting across the Flipper's full 300-to-928 MHz range one channel at a time; you're checking four likely addresses, and one of them is almost always home. That's the difference between "radio is an ocean" and "radio is a short street with four houses on it."
It also explains a frustration you'll eventually hit: on a busy band like 433.92 MHz, lots of devices share the same address. Your doorbell, a neighbor's weather station, and a car's tire sensors may all live there. The band tells you the neighborhood; the protocol and code (Module 3) tell you which house — which is why frequency is the start of identifying a signal, never the end of it.
Two ways to find it: Analyzer vs Test
Compare the real Frequency Analyzer with this course’s synthetic spectrum display. They illustrate related ideas but are not the same instrument.
Frequency Analyzer measures
Sub-GHz → Frequency Analyzer hunts for the strongest signal nearby and reports a detected frequency from its configured scan list. Hold your remote almost touching the Flipper, press the button, and it prints a number.
Use it to discover a frequency you don't know.
Spectrum simulator models
The browser spectrum scope displays synthetic peaks and a noise floor. It is not a real Flipper firmware screen or a calibrated measurement.
Use it to learn how to read a plot, then record real analyzer observations separately.
Why proximity matters so much. The Analyzer works by finding the loudest thing in the room. If your remote is across the desk, the loudest thing might be a neighbor's doorbell, a nearby sensor, or plain noise — and you'll get a wrong or wandering answer. Held a centimeter away with a fresh battery, your remote is overwhelmingly the loudest thing, and the reading snaps to the truth. Close and pressed is the whole technique.
Practice the reflex
Before you chase your real remotes, play a few rounds here. A "remote" transmits somewhere on the dial; your job is to name its band. It trains the exact instinct the Analyzer rewards.
Score five in a row and you'll earn the Tuned In badge — a small nudge that the reflex is sticking.
The gentle math: frequency and wavelength
You can complete this whole course without touching a formula. But one relationship pays for itself, because it quietly explains antennas, range, and why 433 gear looks the way it does. Here it is, once, gently.
A radio wave travels at the speed of light, c ≈ 299,792,458 m/s — call it "about 300 million metres a second." Its wavelength (λ) is the physical distance one full wiggle covers before the next begins. Faster wiggling (higher frequency) packs the wiggles closer, so higher frequency means shorter wavelength. The formula is just that sentence in symbols:
Run 433.92 MHz through it and you get about 69 centimetres — roughly arm's length. A useful antenna is often a neat fraction of that; a quarter-wave for 433.92 MHz is about 17.3 cm, which is why 433 antennas tend to be a few finger-lengths long. Higher frequencies have shorter waves and shorter antennas; that's the whole reason a 915 MHz sensor's stub is stubbier than a 315 MHz remote's whip.
Rather than do arithmetic in your head, poke the calculator — type a frequency and watch the wavelength (and quarter-wave) update:
Why should a beginner care about wavelength at all?
Two payoffs, later. First, antennas: in Module 4 you'll see why the right little antenna dramatically improves range — it's cut to match the wavelength. Second, sanity checks: if a "reading" implies an antenna the size of a room or a grain of sand, you know something's off. You don't need to calculate; you just need the instinct that frequency and physical size are linked.
Lab 1: read three frequencies
Analyze your own remotes
Gear: Flipper + at least three remotes you own (doorbell, LED remote, fan remote, old garage remote…)
- Open Sub-GHz → Frequency Analyzer.
- Hold your first remote almost touching the top of the Flipper.
- Press and hold the remote's button. Read the frequency the Analyzer prints. Write it down next to the device's name.
- Repeat for a second and third device. You're building your first personal frequency map.
- Cross-check a reading against the training remote’s label or manufacturer documentation. Record whether they agree and keep any uncertainty explicit.
Check yourself
Verify the details
Read the primary sources: Flipper: regional frequencies · Flipper: reading signals and presets. Course review: 10 September 2026.