CAT Control and Rig Control Software
CAT — Computer Aided Transceiver — control is the serial or USB interface that allows your computer to read and control your radio's frequency, mode, and other functions. Once your radio is connected via CAT, your logging software automatically records the band and mode of every contact, your digital mode software tunes the radio to the correct frequency with one click, and contest software can instantly QSY to a spotted DX station. CAT control transforms your radio from a standalone device into the centrepiece of an integrated station.
The CAT interface
CAT control uses a serial communication protocol — either over a physical RS-232 serial port (rare on modern PCs), a USB-to-serial adapter, or a direct USB connection on modern radios. The radio and computer exchange commands and responses: the computer can send commands like "tune to 14.074 MHz" or "set mode to USB," and the radio reports back its current frequency, mode, S-meter reading, and other status. Most radios respond to CAT commands within milliseconds, making frequency readout and control feel seamless.
Each manufacturer uses their own CAT dialect. Icom uses CI-V (Controller Interface V), Yaesu uses FIF-232 / CAT-I, and Kenwood uses its own protocol. Software like Hamlib provides a universal abstraction layer so applications can control any supported radio without needing to know the specific protocol.
Modern USB radios
Most current HF transceivers include a USB port that provides both CAT control and audio in a single cable. The Icom IC-7300, IC-705, IC-7610, Yaesu FT-991A, FT-DX10, and Kenwood TS-890S all fall into this category. Connect via USB, install the manufacturer's USB driver if required (Windows), and the radio appears as both a virtual COM port (for CAT) and a USB audio device (for digital modes). This single-cable approach significantly simplifies station setup compared to older radios requiring separate serial and audio connections.
Install the USB driver
On Windows, most radios require a USB driver to create the virtual COM port. Icom radios use a Silicon Labs CP210x or FTDI driver. Yaesu radios typically use a Silabs driver. Download the correct driver from the radio manufacturer's website — not from a generic driver site. On Mac and Linux, the drivers are usually included in the operating system. After installation, the radio appears as a COM port in Device Manager (Windows) or as /dev/ttyUSBx or /dev/cu.usbserial (Mac/Linux).
Identify the COM port
On Windows, open Device Manager and expand Ports (COM and LPT). The radio will appear as "Silicon Labs CP210x USB to UART Bridge (COMx)" or similar. Note the COM port number — you will need it for every software configuration. If two COM ports appear (common with some radios), one is for CAT and one is for firmware updates — the CAT port is typically the lower-numbered one. On Mac/Linux, run ls /dev/tty.usb* or ls /dev/cu.* in a terminal to see available serial devices.
Configure your software
In WSJT-X (for FT8), go to File menu, Settings, Radio tab. Select your radio model from the Rig dropdown (or select Hamlib NET rigctl for Hamlib), enter the COM port, and set the baud rate to match your radio's CAT baud rate setting (typically 9600 or 19200 — check your radio's menu). Enable PTT via CAT or RTS/DTR as appropriate. Click Test CAT — the radio's current frequency should appear. In logging software like Log4OM, the radio setup is in a similar settings area.
Share the CAT port between applications
Only one application can use a COM port at a time by default. If you want both WSJT-X and Log4OM to control the radio simultaneously, use a virtual COM port splitter like VSPE (Virtual Serial Port Emulator) or configure one application to use Hamlib's rigctld daemon as an intermediary — all applications then connect to rigctld, which holds the actual COM port. This is the standard multi-application CAT sharing setup used by most station computers.
| Software | Platform | Primary Use | CAT Support |
|---|---|---|---|
| Hamlib / rigctld | Win/Mac/Linux | Universal backend for other apps | 300+ radios via unified API |
| Ham Radio Deluxe | Windows | All-in-one rig control + logging + digital | Extensive — most popular HRD feature |
| WSJT-X | Win/Mac/Linux | FT8/FT4/WSPR digital modes | Built-in via Hamlib |
| N1MM Logger+ | Windows | Contest logging | Built-in — wide radio support |
| Log4OM 2 | Windows | General logging | Built-in via Hamlib |
| fldigi | Win/Mac/Linux | Digital modes (PSK, RTTY, etc.) | Built-in via Hamlib |
| OmniRig | Windows | CAT sharing server | COM port sharing for multiple apps |
My CAT connection worked once but now shows an error — what happened?
The most common cause is that another application has claimed the COM port. Only one process can hold a serial port open at a time. Check that you have not accidentally opened the radio's programming software, a previous instance of your logging software, or another application that uses CAT. Restart all radio-related software in the correct order: start rigctld or OmniRig first, then start dependent applications. If the issue persists, unplug and replug the USB cable to reset the virtual COM port.
What baud rate should I use for CAT?
Check your radio's CAT or PC speed setting in its menu. Common values are 4800, 9600, 19200, and 38400 baud. The software must match the radio exactly — a mismatch causes garbled or no communication. Higher baud rates give faster response but all standard baud rates are adequate for normal use. The IC-7300 defaults to 9600 baud. The FT-991A defaults to 38400 baud. When in doubt, check the radio's manual for the default CAT baud rate.
Do I need CAT control just for FT8?
Technically no — WSJT-X can operate in split mode where it controls only audio and you tune the radio manually. But CAT control makes FT8 significantly more convenient: frequency readout is automatic, the software can tune to spotted DX stations with one click, band changes are seamless, and logging integration works correctly. If you plan to do any serious FT8 operating, setting up CAT control is worth the 30 minutes of configuration time.