A few months ago, I decided to buy radio interface for digital operation from BD7JAD.
The interface is known as LINK4. It is used for radio CAT interface and digital communication such as SSTV, RTTY, JT65, Echolink, CW etc.. this operation is software dependent.. you need to use the right software for the application and LINK4 does PC-RIG communication. It has USB port (connected to PC), a 9 pin connector (for DATA, CAT & PTT), TX & RX audio level potentiometer and headphone/line out socket at the rear. For the front, it has 4 LED to indicate PWR, PTT, CW & CAT.
It is a very well built device, powder coated metal casing and a professionally assembled PCB with built in USB isolator. The isolation transformer is no longer used in LINK4.
From the picture below, you can see a wire and extra socket which I added as a modification to activate PTT using foot switch.
The reason I did such modification is because I plan to use it as interface for SSB communication using Voice Shaper to process the audio before transmitting. This means, I will be using a microphone connected to the PC and Voice Shaper will do the compression for SSB operation.
To know more about Voice Shaper, you can see HERE
Overall, I like the LINK4 but I found some minor fault.
1. It can pickup sound (such as knocking on the case) and you can actually hear it if you configure the PC built in sound card to "listen" on the C-Media line in. C-Media is the built in sound card on LINK4. I am not sure if it also have similar issue on the C-Media line out which will actually the audio line out to your rig.
2. USB communication suffers from glitch and hanged if the rig & antenna is not properly grounded. I solved this issue by adding a snap in ferrite core on the USB cable and proper grounding of radio.
Nevertheless, I personally think the issues described is minor and can be solved easily without affecting your operation.
If you are thinking to get one, go ahead and try it yourself.