USB Mode

USB Mode

The radio's USB port can serve two different purposes, and you can switch between them right from the front panel:

• CAT mode — the USB port acts as a rig‑control (CAT) interface, so an external computer can read and set your frequency, mode, and PTT for logging and digital software.
• Mouse/Keyboard mode — the USB port acts as a keyboard/mouse input, so you can plug in (or act as) input devices for the Pi.

Open it with Menu → USB.

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Switching modes

1. Menu → USB (shown on the button as USB_Mode).
2. Each tap toggles between the two modes.
3. The button shows the current mode — CAT or MOUSE — so you can see which one is active at a glance.

That's it — the switch takes effect immediately.

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When to use CAT mode

Choose CAT when you want an external computer to control the radio:

• Running a logging program that reads your frequency and mode.
• Running WSJT‑X, JS8Call, FlDigi, or similar on a laptop/PC connected to the radio.
• Any software that expects a hamlib/rig‑control connection.

In CAT mode, point your software at the radio as a hamlib‑compatible rig. The radio's built‑in CAT server handles frequency, mode, and PTT.

If you'd rather run digital software on the Pi itself instead of an external computer, you don't need CAT mode — use the Pi desktop via VNC. CAT mode is specifically for an external computer over USB.

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Configuring your software for CAT

CAT mode presents the zBitx to your computer as a standard USB rig connection. When you plug in, your computer sees two things:

• a virtual COM port (serial port) for rig control, and
• a USB audio interface for sending and receiving audio.

Remember to set the mode to DIGI on the front panel.

Set your logging or digital‑mode software up like this:

Rig / CAT control

• Radio model: select Icom IC‑746.
• CI‑V address: set to 56, if your software asks for one.
• COM port: choose the virtual COM port that appeared when you connected the radio. (The port number varies by computer; pick the one that showed up when you plugged in.)

Audio (for digital modes and voice)

• Input (from radio): Microphone (Source/Sink)
• Output (to radio): Speaker (Source/Sink)

With those settings, programs like WSJT‑X, JS8Call, and FlDigi — and most loggers — will control the radio and pass audio correctly.

The Icom IC‑746 / CI‑V 56 selection is a compatibility profile — you're not telling the software you own an IC‑746, you're picking the control protocol the zBitx emulates so the two speak the same language.

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⚠️ Important: use a data‑only cable for CAT

When connecting an external device for CAT, use a USB cable that does not supply power to the zBitx Pi Zero during normal operation.

The Pi Zero 2 W does not isolate its USB power input from the 5 V rail on the header pins. If a second power source (your external computer, through the USB cable) is connected at the same time as the radio's own supply, the two can backfeed — one supply pushing current into the other. That can cause:

• instability and random resets,
• overheating, and
• potential hardware damage.

How to avoid it — block the power wires on the CAT cable:

• Use a "data‑only" USB cable (the 5 V power wires are absent). These are ideal but can be hard to find.
• Or add a USB power blocker (a data‑only adapter) inline, which passes data but blocks the 5 V. This is the easy, reliable option.

A data‑only adapter that works: https://a.co/d/0d9IruKX

This only matters for CAT mode with an external computer, where a second cable to a powered device is involved. It's the single most important thing to get right before wiring the radio to a PC — do this before your first CAT connection.

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When to use Mouse/Keyboard mode

Choose MOUSE (Mouse/Keyboard mode) when you want the USB port to handle input devices — for example, using a keyboard/mouse with the Pi's desktop environment.

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How it works (briefly)

Behind the scenes, the front‑panel button asks the Pi to run its USB‑mode helper, which reconfigures the port and reports back the new mode. The button then updates to show CAT or MOUSE. Because the radio remembers and displays the active mode, you always know which role the USB port is currently playing.

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Troubleshooting

After switching USB mode, reboot the radio for the change to fully take effect. The mode switch is applied immediately, but the USB port's new role isn't always fully active until the Pi restarts — especially the first time you switch, or when moving between CAT and Mouse/Keyboard. If your external computer or input device doesn't behave as expected right after switching, shut down cleanly (Menu → SHUTDOWN → OK, wait for the LED) and power back up, then reconnect.

Symptom	Fix
Mode change didn't seem to work	Reboot the radio — the new USB role may need a restart to fully apply (see the note above).
Button doesn't change mode	Make sure your Pi software and panel firmware are current — USB‑mode control is a newer feature. See Upgrading.
External software can't see the radio	Confirm the button reads CAT, check your USB cable, reboot after switching, and point your software at the correct port as a hamlib device.
Software connects but won't control the rig	Check the CAT settings: radio model Icom IC‑746, CI‑V address 56, and the correct virtual COM port.
No audio to/from digital software	Set the audio devices: input Microphone (Source/Sink), output Speaker (Source/Sink).
Keyboard/mouse not working	Confirm the button reads MOUSE, and reboot if you just switched from CAT.
Radio resets, overheats, or acts unstable on CAT	You may be backfeeding power through the CAT cable — use a data‑only cable or USB power blocker (see the warning above).

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Related: Voice & Digital Modes » · VNC & Remote Desktop »