A Little Background
Using digital modes was easy when I first joined MARS (now the Military Auxiliary Radio System) back in the 1960s. There were two choices: CW and RTTY. Now, in addition to CW and RTTY, there are a number of different modes that can and must be used. This also means that the HF transceiver used for MARS must be able to connect to more than one hardware accessory.
The issue comes down to operating multiple digital modes in real-time. No single accessory device (HF Modem, PC, sound card interface) can handle all the modes. Even if a single device could, most operators have ones they prefer and that meet their needs better than some “does-all” unit or software package could. And then there are other devices that can be connected to a transceiver. A prime example is a phone patch.
Unfortunately most HF transceivers have a single accessory jack on the back. In many cases that forces the MARS operator to have to unplug one device and plug in another device … in real-time. This is time consuming and error prone.