Through the years I have build many types of Soundcard Interfaces. Some KISS models and others with micro controllers. You can find some of the interfaces HERE. They all enabled me and many others to work various digital modes. Nowadays many of the new radios do not need the conventional soundcard interface to allow you to work digital modes. Several years ago I found The USBLink design by Julian Moss G4ILO now SK. I kept a copy of his article on my Soundcard Interface file for many years long before Julian went silent key. About two weeks ago I paged through my file and found the article. Now I do have several types of Soundcard Interfaces in my shack but this interface article gave me an idea that I will discuss in Part 2. First off I need to build the USBLink Interface and test it live on the air. The article of the USBLink is available HERE.
This interface is in my opinion a KISS unit with no bells and whistles. Herewith a few features that makes the unit a KISS interface:
1. No Serial to USB interface / cable needed to handle PTT.
2. No 1 : 1 (600 ohm) isolation transformers needed.
3. Relatively low cost to construct the unit.
4. Relatively small size compared to other homebrew interfaces. (Ideal for portable operation.)
5. Does not use opto-isolation of the PTT line. (Not needed)
6. Inexpensive USB Sound Card can be used. (Chinese cheapies will also work but I would rather buy a better quality product.)
7. Project can be constructed on a piece of veroboard.
8. No dedicated power supply needed for the Soundcard Interface.
9. Diodes added for PTT transistor and radio protection. (I would however add another switch to cut off the PTT line going to the transceiver to prevent accidental PTT activation when unit is left unattended.)
10. Plug and Play Unit - No drivers to install.
Finally: This is a simple low cost circuit which works well and allows you to operate sound card digital modes without tying up your computer's built-in sound card. I constructed this interface and tested the interface on VHF. In part 2 I will provide feedback on how the interface behave on HF but from what I observed using a VHF transceiver it should work just as well on HF. Although I am not in favor of using VOX in any way in amateur radio, I do not foresee any issues using this interface attended. I would not leave this interface unattended and therefor suggested the additional switch between ground and PTT to prevent accidental transmissions.
Images: (Click on images for larger view.)
