Listening

Choose Start scanning. The receivers sweep the bands you selected. When a channel is louder than the squelch level, the dashed line on the chart, the channel opens and you hear it.

Up to three channels can be open on one receiver at the same time. They are placed apart in the stereo image, from left to right, so that they can be told apart.

The chart ↑

The chart has one bar per channel. Each bar shows the spectrum inside its channel, with a bright edge along the top. A voice fills its channel. An unmodulated carrier appears as one narrow spike. A signal leaning to one side of its channel may be off frequency.

The white mark across a channel is the channel's level, the value the squelch is compared with. A bar with a label above it is being heard. Dashed bars are channels the scanner passes over: locked out, muted, or skipped for a while.

Not scanned marks the part of a band that no receiver covers. A dimmed tuning is one its receiver is not watching at the moment, because the receiver is holding a channel on another tuning.

Show the waterfall adds the waterfall under the chart: the spectrum over the last half minute, newest at the top. Each transmission appears as a bright streak under its bar, for as long as it lasted. Drag the handle under the waterfall to change its height, up to a few minutes of history. Double-click the handle to restore the usual height.

Settings › Chart sets how often the chart is drawn, 10, 30 or 60 times a second, and how finely each channel is resolved: Normal, Fine or Finest. Drawing less often saves power. Finer resolution shows more of a signal's shape and makes the sweep slightly slower.

Open channels ↑

Each open channel has these controls:

• Stay on this channel: the receiver keeps listening to this channel, also while it is quiet, so that you hear the reply. Choose it again to let the scanner move on.
• Mute: keep receiving the channel without playing it.
• Lock out: never stop on this channel again. Lock out until the app is restarted does the same for this session only.
• Name: type a name, and the channel is saved.

Play speech only, in Settings › Listening, keeps a channel silent until someone speaks on it. Tones, data and empty carriers are not played. The first words are kept and played as well. This setting is off by default.

When every receiver is busy, move on after a while, on the same page, applies when a transmission occupies each of your receivers and nothing else can be heard. The receiver that has been on its channel the longest leaves it after the time you set, one minute by default, and continues sweeping. It does not return to that channel until the transmission has ended. A channel you are holding is never left. Switch the setting off to always hear a conversation to its end.

Morse code ↑

Every open channel is monitored for Morse code: a repeater sending its call sign, an aviation beacon's identifier, radio amateurs in CW. While Morse is being received, the channel is marked ·– and the text decoded so far is shown under the channel's name. When the transmission ends, the text is kept in Heard recently and in Conversation, marked Morse.

A transmission may contain both Morse and speech, for example a call sign followed by a voice. Each part is shown as what it is, in the order received: Morse with the decoded text, Speech with the transcription. When speech to text is on, only the speech is transcribed, never the Morse.

Read Morse code, in Settings › Listening, is on by default.

Radio amateurs send Morse by keying an unmodulated carrier (CW). The CW mode is made for it: the carrier is heard as a steady tone of about 700 Hz through a narrow filter, 500 Hz wide, which keeps neighbouring stations out. A station slightly off the channel's frequency is heard at a slightly higher or lower pitch.

Amateur radio includes the CW segments of 2 m and 70 cm as bands of their own, 2 m CW and 70 cm CW, in the CW mode. For a CW range or channel of your own, choose CW as the mode, enter the carrier frequency, and set a width of 0.5 kHz. CW received through USB or LSB is decoded as well.

The demo includes both cases: a repeater that identifies itself in Morse before a voice follows (Repeater, on 2 m), and a CW station calling on the CW segment of 2 m (CW calling). A scanner arriving in the middle of a transmission omits the letter in progress rather than guess it, so a decoded call may begin one letter late.

What to scan ↑

Settings › What to scan is one list. Everything at the top switches the whole list on or off, except FM radio.

Below it, each group is a kind of listening: Aircraft, Boats and ships, Amateur radio, Walkie-talkies. Each group has a switch. The bands in a group are rows under it, each with its own switch, the number of channels it holds, and, with several receivers, the receiver that scans it.

A group whose bands are partly on shows a mixed mark. Selecting it switches all of its bands on; selecting it again switches them off.

FM radio stands alone. A broadcast station never stops transmitting, so while FM radio is on nothing else is scanned, and switching any other band on switches FM radio off.

My ranges holds your own frequency ranges. Add a range of your own takes a name, the lower and upper frequency in MHz, the channel spacing and width in kHz, and the mode. Other bands holds the bands of your region that belong to no group.

Saved channels has one row per tag used by your saved channels, and Without a tag for channels without one. A row switched on means those channels are scanned, whatever their band's switch says. A band off with a tag on scans only the channels with that tag.

To scan only a handful of frequencies of your own: save them under a tag, switch Everything off, and switch that tag on.

With several receivers, each of these rows has a receiver choice too, which takes precedence over the band's. For example, put the tower's channel under a tag assigned to the receiver with the airband antenna: that receiver listens to the tower while the other scans the rest of the airband. The choice applies while the row is on; a row switched off leaves its channels to their band.

Left out of scanning, below the list, holds frequency stretches that the scanner always passes over, in whichever band they lie.

The lists ↑

• Heard recently: every channel active today, newest first. Recordings can be replayed from here. Earlier days are in the activity log.
• Conversation: the transcriptions, when speech to text is on (Recording and speech to text), and the decoded Morse.
• Saved channels: the channels you have named, with their tags. Each row shows whether the channel is currently scanned, and can lock it out, mute it, or let it in again. The tags' switches are on the What to scan page.
• Locked and muted: where locks and mutes are undone. Each channel is listed with its name, when it has one.
• Set aside: channels that KaikuSDR holds back on its own, separately from your locks. See below.

Set aside

Some channels carry no station. A channel that carries a steady, unmodulated carrier for five seconds; a channel that stays open for eight seconds with no speech on it (on a CW channel, with no Morse); or a channel that opens again and again for a moment with nothing said, five times in two minutes, which is typical of data bursts.

The usual cause is interference from the computer's USB ports, a hub or the dongle itself. Such a channel would otherwise occupy a receiver for as long as the interference lasts. KaikuSDR sets it aside and the list shows the reason and the time.

A channel returns on its own when a much stronger signal appears on it, which is a station over the interference, or, for a carrier, as soon as it is modulated. Let in brings it back at once and never sets it aside again. Lock out turns it into a lock of your own.

Nothing here is decided by the frequency, only by what is received on it at the time.

Audio for other programs ↑

Settings › Sharing has Audio for other programs. When it is on, other programs on this computer, such as a decoder or a recorder of your own, can take the audio you hear from the address shown there: raw 16-bit stereo audio at 48,000 samples a second. Only programs on this computer can connect.

Profiles ↑

A profile is a copy of all settings under a name: what to scan and the region, the stretches left out, squelch and volume, listening, recording, speech to text, chart and sharing.

Set everything up as you want it, open Settings › Profiles and save it under a name, for example "Home". Set things up differently and save "Cottage". From then on, selecting a profile applies all of its settings at once, also while scanning.

The page shows which profile is in use, or that the current settings are not saved as one. Saving under an existing name replaces that profile.

Not part of a profile: the receivers and their own settings, which belong to the connected hardware, and what you have learnt: saved channels, names, your own ranges, locks and mutes. These stay as they are whichever profile is in use.