Channels

A channel takes a Device's IQ and turns one frequency into audio, messages, or pictures. The channel you pick decides the mode: AM, WFM, ADS-B, and so on. Decoders lists them all.

Add a channel

1. Press + Add and pick a mode.
2. Wire Device iq to the channel's iq.
3. Set the channel frequency.
4. Wire the outputs you need:

To swap the mode, right-click the channel and choose Replace with…. The frequency and squelch stay; wires the new mode has no port for are dropped. m and M cycle NFM, WFM, AM and SSB.

Tuning

Use the channel dial, drag its marker on the Scope, or use the keyboard. Scroll or press the arrow keys over a dial digit to step it. Typed frequencies are in MHz unless you add Hz, kHz, or GHz. You can set frequencies before a radio is connected.

Auto and manual

Every Device starts on Auto, shown by the lit radar button next to its dial. It places its window over as many wired channels as its sample rate can hold, and keeps its own DC spike off them. The count on the Device, such as 2/3, shows how many it hears. To hear more, raise the sample rate or move some channels to another radio.

Tuning the Device itself, from its dial, the keyboard, or the Scope, asks first and then switches it to Manual. The radio then stays put, and channels outside its window wait until it covers them again. Press the radar button to return to Auto. Use Manual to watch a fixed band, or when no channel is wired.

The lock beside a dial freezes that frequency. Locking a channel does not lock its Device.

Several radios

Wire a channel to more than one Device and it runs on whichever radio hears it. Radios on Auto split their channels so as many as possible are heard. The channel face names the radio carrying it. While a scanner, signal hunt, recording, or network export uses a channel, it stays on its radio until that stops.

Sample rate

Each channel runs at a rate set by its mode. The Device's IQ is resampled to match, so any Device rate works as long as the channel's full bandwidth fits inside the Device's window.

When the Device rate equals the channel rate, resampling is skipped: ADS-B runs at 2.4 MS/s, DAB and GNSS at 2.048 MS/s, ATV at 16 MS/s. Use the lowest rate that covers your signals. It saves USB bandwidth and CPU.

Squelch

Squelch mutes audio when nothing is there. Only channels with audio have it.

The level meter marks the threshold. Auto learns the floor while the channel is quiet, so a signal that never stops can be mistaken for noise. Once squelch is open, the floor cannot rise and cut off a long transmission. Turning Auto off keeps the threshold it reached. Analog channels report calls on events only with squelch on.

NFM also has Tone squelch:

Scrambler undoes voice inversion: set the Carrier, 1.5 to 4.5 kHz, or pick Auto. Compander expands audio 2:1 for links that compress it. Leave it off for ordinary NFM.

Noise blanker

The Blanker on audio channels removes impulse noise from the IQ before filtering. A lower threshold removes more, but can damage the signal.

IF filter

The IF chip shapes the IQ ahead of the demodulator, so a neighbour is gone before it can capture an FM receiver or swamp a decoder.

• Edges move either side of the passband in, one side at a time. Cut the side a stronger adjacent station sits on.
• Notches remove narrow interferers such as carriers and birdies. Each sits at a radio frequency, so it stays on its interferer when you retune.

The spectrum shades the narrowed passband and marks each notch in red.

Audio FX

Wire a channel's audio through an Audio FX node to process what you hear. The raw audio stays available on the channel's other wires, so a recorder can keep it while a Speaker plays the cleaned version. Chain several nodes to stack effects. Stages run in this order, all off by default:

DPDFNet is trained on speech. Leave it off for music, data tones and CW.

Pick a DPDFNet model, then press the download button next to it. DPDFNet 2 is light; 8 sounds better and costs more CPU. The button next to a downloaded model removes it.

Speaker output

Out on a Speaker picks its sound device. Give each decoder program its own Speaker and virtual device:

In a browser, press Show device names once to list devices by name.

Filter events

Put an Event filter between a decoder and its outputs. Every rule you set must match.

A rule that does not apply to an event is ignored: a talkgroup rule never judges an aircraft. A drop filter with no rules drops nothing. Chain filters to combine them, for example keep POCSAG, then drop messages containing TEST. A filter only affects events that arrive after it is set.