Part of our Getting On The Air: Modes, Operations, and Making Contacts guide.
If you run any station software (logging, digital modes, or a full suite like Ham Radio Deluxe) you have run into the term CAT control. It comes up constantly, and it is the invisible glue that lets your computer and your radio work together. Here is what CAT control is, in plain language.
What CAT control is
CAT stands for Computer Aided Transceiver. CAT control is simply the two-way communication link between your computer and your radio. Over that link, software can read what the radio is doing and tell the radio what to do. It is a data connection carrying commands and status, separate from the audio your radio sends and receives.
Through CAT, your software can:
- Read and set the frequency
- Read and change the mode (SSB, CW, FM, digital, and so on)
- Key the transmitter (tell the radio to transmit, often called PTT)
- Adjust settings like power, filters, and VFOs
- Report signal strength and other status back to the software
Why it matters
CAT control is what makes a lot of modern operating possible. A few examples:
- Logging. Because your logging software can read the radio’s frequency and mode over CAT, every contact you record is automatically stamped with the correct details. No manual entry.
- Digital modes. Programs like WSJT-X and Fldigi use CAT to set your frequency and key the transmitter at exactly the right moment. Without it, running FT8 would be a manual mess.
- Remote and computer operation. CAT lets you control the whole radio from the screen, which is the basis for operating remotely or from a fully computer-driven station.
- Band and frequency sync. Click a spot in a spotting program or a DX cluster and CAT can instantly put your radio on that frequency.
How it connects
Physically, CAT control usually runs over a serial connection. On older radios that often meant a dedicated CAT or CI-V port and a special cable, sometimes with a USB-to-serial adapter in between. On many modern radios, a single USB cable carries everything, and the radio presents a virtual serial port to your computer for CAT alongside its built-in sound card for audio.
Each manufacturer has its own command set. Yaesu, Icom (which calls its system CI-V), Kenwood, and others each speak their own dialect, which is why software asks you to select your specific radio model. Once you tell the software what radio you have and which serial port and speed to use, it knows how to talk to it.
CAT versus audio: two separate jobs
It is worth being clear on this because it trips people up. For digital modes, your computer needs two connections to the radio: CAT control (the data link for commands and keying) and an audio path (to send and receive the actual sounds). These are separate functions. On a radio with a built-in USB interface, both travel down one cable. On a radio without one, you might use a CAT cable for control and a device like a Digirig or other sound-card interface for the audio. Knowing they are two different jobs makes troubleshooting much easier: if the radio changes frequency but you get no decode, your CAT is fine and your audio is the problem, and vice versa.
The takeaway
CAT control is the command-and-status link that lets software drive your radio. It is what allows your logging program to stamp contacts automatically, your digital software to key up on cue, and your whole station to be operated from a computer. Once you have it set up (the right radio selected, the right serial port and speed), it largely disappears into the background and just works, quietly powering most of the software features you rely on.