Find a free frequency window
Set the threshold, read the free-channel list, zoom and re-sweep, use the two waterfalls, listen to a carrier, and compare scans.
On this page
A scan is only worth as much as the room it was taken in. Run it with the venue's other gear switched on — video walls, LED, other companies' wireless, the house system. You want to see the band as it will be during the show, not as it is in an empty hall at 9am.
Find a window
- Start a scan and let it run for a few passes.
- If the threshold sits too high or too low for the room, click Suggest threshold or press T. It sets the line to the median level of the current scan plus 6 dB, which lands just above the noise floor. Drag the line to fine-tune.
- Open the Free channels card. Each row is a window with its start, end and width in MHz. Wider windows are listed first.
- Click a row, or drag on the spectrum, to zoom in. Scan this range re-sweeps only the zoomed part with finer resolution.
Run a 3-sweep burst (in Setup) rather than a single pass before you trust a window. Intermittent signals — a comms pack that keys up now and then, a neighbour's mic on standby — show up on the second or third sweep.
If everything reads as occupied, or everything as free, the threshold is wrong for this room rather than the room being unusual. Suggest it again after a fresh sweep.
Use the waterfall
The Live view has two waterfalls, and they answer different questions.
- The live waterfall scrolls in real time at a fixed centre frequency. It shows short bursts a sweep would miss. It works on devices that stream raw IQ: RTL-SDR, HackRF, Airspy, SDRplay, and demo mode.
- The sweep history strip adds one row per full scan, on every device. Leave it running through a soundcheck and you get a picture of how the band changes over an hour.
On a tinySA or RF Explorer the live waterfall card shows a note explaining that it needs an IQ device; the sweep history still works. See Supported hardware.
Listen to a frequency
With an RTL-SDR you can hear what is on a frequency. Click Listen next to any entry in the My equipment card. Spektra RF FM-demodulates it in the app with a squelch and a level meter.
It is a monitor, not a receiver: it tells you whether the signal on 614.400 is your vocal mic or the venue's old system that nobody switched off.
Listen only works on the RTL-SDR path — not on tinySA, RF Explorer or SoapySDR devices. And it demodulates FM, so analogue systems (Shure UHF-R, SLX, BLX; Sennheiser G3/G4) come through as audio, while digital systems (ULX-D, QLX-D, Axient, EW-D, Digital 6000, Sony DWX) sound like noise. That is expected, not a fault — hearing noise still confirms a carrier is there.
Save and compare scans
Press S, or click Save scan, to keep the current sweep under a name. Saved scans live in the Saved scans view. Open one to overlay it on the live spectrum.
That is how you compare an afternoon scan with the situation at doors, or last year's scan of the same venue with today's. You can also bring in a scan somebody else made on different hardware — see Export and import.
Keyboard shortcuts
| Key | Action |
|---|---|
| Space | Start / stop scanning |
| S | Save the current scan |
| T | Suggest threshold (median of the scan plus 6 dB) |
| R | Reset the scan settings |
| + / − | Zoom in / out around the point you last clicked |
| 0 | Reset the zoom |
| Esc | Close a dialog, or drop the zoom anchor |
| ? | Show this list in the app |
The letter keys work on any keyboard layout. Shortcuts pause while a dialog is open.
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