Over the years, I have noted there is some 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 and useful information.
 

Lets first look at CAT Control

​

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

Manufacturers sold CAT control products to interface between your PC and your transceiver. Icom produced the CT-17, Yaesu the FIF-232 & CT62 interfaces and Kenwood the IF232C.

If you look at my Icom, Yaesu, Kenwood and Xiegu shops, you will see my CAT Interface products are considerably better value than the manufacturer offerings. Many of our Digimode products also have a built-in CAT interface.

 

There are a many free (and paid for) CAT control applications available for PC's running Windows, Linux and MacOS such as Ham Radio Deluxe, Super Control, Commander and many more. Mainstream Digimode Applications such as WSJT-X, Fldigi, MixW etc also include CAT functionality as well as the Tx/Rx audio interfacing.

As modern transceivers have bi-directional CAT data, any change to the transceiver 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 and Digimode 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 can be a mix of TTL, RS232 with later transceivers allowing CAT commands via a USB socket on the radio.

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 CAT data is on a common wire and up to 4 transceivers can exist on the same CI-V bus with each radio having a unique CIV Address.

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.

Kenwood transceivers also have a CAT system. Some 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.

 

Xiegu transceivers such as the X5105 and G90 have a 3.5mm jack socket CAT (COMM) port on the side of the radio. Again, these are TTL levels with separate lines for TxD and RxD on the tip and ring of the connector. 

The original Xiegu X108G also has CAT control. This is a USB Micro connector on the rear of the radio and all you need is a USB A to micro USB cable similar to an Android type phone charger lead to utilise it. You need to install the X108G drivers (off the web) to utilise this but it is really easy.

 

All Xiegu transceivers actually emulate the Icom IC-7000 CAT protocol and CI-V address.

​

Digital Mode Operation
 

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.

So we are talking about modes such as PSK31, FT8, JT9 and others too many to mention. 

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. Only with RTTY, you would have just two tones. In many Digital modes, your sound card can be generating many tones simultaneously. For example FT8 is 8 tones each just 6.5Hz apart from adjacent tones.

In the case of modern Digital modes, your PC's sound card 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 code and 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 IF bandwidth into the sound card 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 pass-band of your receiver.
 

In latter years modes such as FT8 using the WSJT-X software has become incredibly popular.

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. 
 

​