Klar — clear. Funk — radio. KlarFunk sweeps the UHF wireless-mic band in seconds on an SDR from around €40: live spectrum with waterfall, clear free/occupied verdicts, and a Frequency Advisor that turns the measured gaps into an intermod-safe, printable coordination plan in one click. Built in Germany, for stages that do not get a second take.
KlarFunk covers the whole pre-show RF workflow — sweep the band, read what's free, lay out your channel plan, and hand off clean numbers to the stage.
Full 470–700 MHz UHF sweep in a few seconds, ~1-second cold start, band presets for DECT and 2.4 GHz — hardware permitting up to 6 GHz. Live waterfall works on RTL-SDR and in demo mode. Every other device gets the sweep-history strip instead — one row per completed sweep, on every device.
Coordinated, intermod-checked suggestions placed inside the actually measured free windows — third-order products of two transmitters (2A−B) and of three (A+B−C), Robust and High-density profiles, and deterministic results: a reprinted plan always matches the printed one.
RTL-SDR (from ~€40), tinySA & tinySA Ultra and RF Explorer — auto-detected on plug-in. HackRF One and Airspy are recognised too (Apple Silicon macOS only — hardware-unverified). No hardware yet? Demo mode generates a synthetic spectrum for training.
Not a dumb threshold: KlarFunk distinguishes your own carriers (green) from contention on your channel (amber) and unknown interference (red) — with a suggest-threshold helper for the noise floor.
Shure, Sennheiser, Lectrosonics, Sony and budget channel-wheel gear — group/channel picks resolve to exact MHz. Regulation overlays for 14 regions tint TV whitespace and give each device a license verdict.
On an RTL-SDR, FM-demodulate and listen to any parked frequency with squelch and level meter (FM only — digital wireless sounds like noise). Save and compare sweeps, export scans as CSV/JSON — and hand guest crews the Advisor's coordination CSV or printable A4 PDF with spectrum snapshot.
The same view you'll run at the venue — captured here in the free browser demo on a synthetic sweep: 10 free channels, 9 occupied ranges, the noise threshold and the channel plan overlaid.
No rack of gear, no lab analyzer, no install marathon. A dongle and a double-click.
Connect a supported analyzer — KlarFunk auto-detects it and cold-starts in about a second. No Python, no Homebrew, nothing to compile; on Windows, run 'KlarFunk - Install RTL-SDR Driver' once from the Start menu first.
Sweep the UHF band in seconds, watch the waterfall (live on an RTL-SDR, sweep history on every device), and read the 3-state verdicts: your carriers green, contention amber, intruders red — every usable gap listed.
One click on the Frequency Advisor places intermod-checked frequencies inside the measured gaps — print the A4 coordination sheet and hand it to the stage.
The interface ships in seven languages and switches instantly — no reload. Dark mode for the FOH position, light mode for daylight load-in, with a tunable accent so it fits your rig.
The coordination work that actually decides your show day — done properly, deterministically, and for a fraction of the cost of a dedicated suite or lab hardware.
| Capability | KlarFunk Best value |
Free manufacturer software | Pro coordination suite | Lab spectrum analyzer |
|---|---|---|---|---|
| Typical cost | €49 + €40 dongle | Free | typically €1,000–4,000 | typically €2,000–10,000+ |
| Live RF scanning + waterfall | ✓ | RF scans | ✓ | ✓ |
| Automatic free-channel detection | ✓ | Not stated | ✓ | — |
| Intermod check (IM3: 2A−B and A+B−C) | ✓ | Not stated | ✓ | — |
| Own-carrier vs. interference detection | ✓ | Not stated | Partial | — |
| Printable coordination sheet (PDF) | ✓ | Not stated | ✓ | — |
| Multi-region regulatory overlays | ✓ 14 regions | Not stated | ✓ | — |
| Listen to a frequency | FM audio, RTL-SDR only (digital systems sound like noise) | Not stated | Not stated | Not stated |
| Absolute dBm | On tinySA / RF Explorer; relative dB on RTL-SDR | Not stated | Not stated | ✓ |
| Controls your receivers | No | ✓ that maker's | Not stated | — |
| Not tied to one maker's receivers | ✓ | Mainly one maker | Not stated | ✓ |
| Runs on a low-cost USB dongle | ✓ | Not stated | — | — |
| Pocket-sized & portable | ✓ | Not stated | Laptop + receiver | Bench unit |
“Not stated” means we make no claim either way. Other prices are typical ranges, not quotes.
DE, AT, CH, UK, EU/CEPT, US, FR, NL, BE, IT, ES, AU, JP and CA. Each region's table comes from its regulator's documents. Every device you register gets a verdict: license-free, registration required or forbidden. The Advisor never suggests a frequency the table marks as forbidden, and a band with no source reads “Outside known regulatory bands”.
A planning aid, not legal advice. Check the current national rules before a show.
An RTL-SDR costs about €40 and covers the whole 470–700 MHz UHF mic band. It is a receiver stick, not a lab instrument.
Live waterfall and Listen. Levels are relative dB, not calibrated dBm: the shape of the trace and where it sits against the threshold is what counts.
Calibrated absolute dBm from the analyzer's own firmware. No live waterfall: you get the sweep-history strip, one row per completed sweep. No Listen.
Less dynamic range and coarser readings than a lab spectrum analyzer. Two scanners on the same antenna can differ by 10–20 dB.
When you need levels you can quote in dBm, use an analyzer. When you need measurements someone signs off, use a lab instrument.
A ~€40 RTL-SDR, a tinySA or an RF Explorer — auto-detected on plug-in. Or start in demo mode with no hardware at all.
Ships as a compact desktop app for macOS (Apple Silicon & Intel) and Windows. No Python, no Homebrew, nothing to compile. On macOS there's nothing to install — the RTL-SDR library ships inside the app. On Windows, run 'KlarFunk - Install RTL-SDR Driver' once from the Start menu (the installer puts it there), then plug in and go.
KlarFunk is not notarised by Apple yet. On first launch, macOS will block it once; the Getting Started guide shows the one-line Terminal command that clears this.
Works fully offline at the venue. No account, no telemetry; it binds to localhost only. It goes online only when you ask: once to activate a licence key with Gumroad, and for the update check, which is off by default.
Download free — no account — and every install runs a 14-day full-feature trial. To keep scanning real RF, buy a key once on Gumroad for €49 and enter it in the app: 3 computers per key, updates for the version you own, no subscription.
One app, two licences. KlarFunk's desktop app — the shell you install and the interface you see — is proprietary software covered by the KlarFunk EULA. The scanning engine inside it is free software under the GNU GPL v3 (or later), and its complete source code is published here with every release, so you can read it, build it and change it.
| Version | Download | SHA-256 |
|---|---|---|
| 4.0.0 | klarfunk-engine-src-4.0.0.zip (188 KB) | ce30a81cab170993247ea4aa08e9b590b0d6386bee1fb3a707a53f8e49aff8ba |
| 3.19.0 | spektra-engine-src-3.19.0.zip (180 KB) | cdbb16a0d7db9af5b1f257f3e2d5ab43afe55df28e8a5c413700ec53b21be224 |
The archive corresponds to the engine bundled in the 4.0.0 installers. Source for the native libraries listed in the third-party notices (librtlsdr, libusb and friends) is available from their upstream projects or on request from support@squaresmile.de.
Questions about licensing: support@squaresmile.de
Download KlarFunk free — no account needed. Every install runs a 14-day full-feature trial; after that, a license key from Gumroad keeps it scanning real RF.
Free download · 14-day full-feature trial · then €49 one-time license, 3 computers per key · updates for your major version · Which Mac? Apple menu → About This Mac
The Squaresmile suite
Tools marked Free are yours the moment you sign up; Premium tools and plugins are paid. One account keeps the whole toolbox with you from gig to gig — the browser tools need no install and no app store.
Show day
Show ClockPremium
Stage timer & run-of-show with 3 s crew sync
Stage Plot GeneratorPremium
Stage plots, input lists & DMX patch in one doc
SetlistForgePremium
Setlists with timing, keys & royalty reports
RiderSmithPremiumComing soon
Tech riders in 11 languages, assembled from your tools
SpectraSenseFree
Ring-out assistant — the ringing frequency, note, GEQ band & a cut to start with
Plan the rig
RF CoordinationFree
Find safe wireless-mic windows for DE / UK / US / EU
PowerSenseFree
Loads per phase, cable checks & distro headroom
RoomSenseFree
Acoustic reference: room modes, SPL, LUFS & EQ
MicSenseFree
Mic reference for live — specs, response curves & polar patterns
Train your senses
SoundSensePremium
Ear training for sound engineers — 33 modules
RiggingSenseFree
Bridle & truss statics, taught step by step
Studio & prep
ClickSmithFree
Turn any song into an L/R click track (WAV)
BPM ForgeFree
Tap tempo, metronome, tuner & per-song setlists
PitchSenseFree
Hz ↔ note converter, cents meter & reference tones
TempoSenseFree
Hears the tempo — live BPM, ÷2 / ÷4 / ÷8 layers, delay times & MIDI out
LoudSenseFree
LUFS, true peak & clips for any file — verdict per platform, nothing uploaded
Desktop & plugins
