There seems to be a fair bit of confusion around what CAT control does and what Digimode operation is. Often they are assumed to be the same. On this page, I will put my spin on what it is all about and give you some pointers to useful reference articles and how to get your Radios set up.


CAT Control 

CAT Control is a generic term used to describe how your personal computer can remotely control the frequency and modes of your transceiver. The communications (in general) are bi-directional but some very early transceivers could only receive commands from the PC.

The manufacturers sold products to interface between your PC and the transceiver to allow you access to CAT control. Icom produced the CT-17, Yaesu the FIF-232 plus CT62 interfaces and Kenwood the IF232C.

If you look at my Icom, Yaesu and Kenwood shops, you will see my versions of the interfaces which come in RS232 and USB format.

There are a many free (and paid for) CAT control applications available for PC's running Windows, Linux and MacOS.

As time has gone by, the CAT control feature set of transceivers have become more sophisticated allowing functions such as Tx/Rx switching, filter selection, memory management and much more.

As modern transceivers have bi-directional CAT data, any change to the transceiver settings from the front panel are also picked up by the software keeping the PC software and transceiver in sync. Great for logging applications which are often built into the CAT control applications.

So why the phrase CAT Control?

Yaesu introduced the (C)omputer (A)ided (T)ransceiver protocol in the early 1980's. The name seems to have stuck despite the protocols and interfaces being very different between manufacturers and transceivers.

Yaesu CAT ports on most transceivers are TTL level and so an interface is required between the radio and the RS232 or USB port on your PC which is where my CAT products come in!! Later Yeasu transceivers use RS232 ports for the CAT control.

Icom followed suit with the CI-V interface for their products. CI-V I hear you ask? Well this actually stands for (C)ommunications (I)nterface version 5. Icom took a different route where the Tx/Rx data is on a common wire and up to 4 transceivers can exist on the same port.

The radios and software use a CSMA/CD (Carrier Sense Multiple Access with Collision Detection) and will resend the data if they detect collisions. Again, the levels are nominally TTL and an interface is required to connect between the radio and your PC's RS232 or USB port.

Kenwood transceivers also have a CAT system. Early transceivers required an additional PCB or chips to be installed to enable the function. Once installed, the Kenwood CAT interface was broadly the same as Yaesu with separate Tx and Rx data lines. However, the TTL levels are inverted with respect to Yeasu. Later Kenwood transceivers have an RS232 port.

Digital Modes

This is a general term used to describe the various AFSK (Audio Frequency Shift Keying) modes that can be employed to communicate on the ham bands.

Most digital modes have much in common with RTTY where a terminal unit would toggle the FSK tones on the transceiver and decode the received signals.

In the case of modern Digital modes, your PC's soundcard generates the tones to modulate the transmitter and the software acts as the terminal unit. The performance of the PC is used as a digital signal processor to decode the audio using suitable software.

Having the PC carrying out clever maths (Fast Fourier Transform) on the received audio, the Digimode software can do clever tricks such as employ very tight filtering on the audio allowing the software to decode very low level signals even when there may be high level adjacent transmissions. Much akin to having an expensive CW filter installed.

Generally, you would leave your transceiver in USB mode and let the full audio bandwidth into the soundcard and the software does the rest.

Probably the most popular Digital mode everyone want to start off with is PSK31. This is a phase shift keyed mode unlike RTTY which is frequency shift keyed. The baud rate of PSK31 is just 31 bits per second. The beauty of this sort of mode is that you need very little power, it is very bandwidth efficient allowing multiple signals within the IF passband of your receiver.

What is generally critical with these modes is that you need your transmitter to be operating as linearly as possible. Well out of AGC is desirable. 

There are many more Digital Modes so have a look at the sub-menus from this page.