[Elecraft] K2 & Aux Digital Mode Connection Box

[Bill Coleman]

On May 29, 2005, at 10:15 AM, lbailey at aep.com wrote:

> Anybody have any experience with the various auxiliary connection  
> boxes
> for running digital modes with your K2 & software from your PC.   
> Comments?
>  Suggestions?

I recently built such a box that I could use with CocoaModem, a  
RTTY / PSK program for MacOS X.

My unit is pretty simple, and only took me an evening to build. I use  
a 600:600 ohm transformer and a 8:1000 ohm transformer. The 8:1000  
transformer goes between the headphone jack (8 ohm side) and the mic  
input on the computer. The 600 ohm transformer connects between the  
computer output jack and the microphone. This allows complete ground  
isolation between the computer and the K2.

I use a couple of 25 ohm resistors as loads for the computer  
headphone output, and I have a 500 ohm fixed and 5000 ohm variable  
resistor so I can adjust the level into the microphone. I use just  
barely enough audio to keep the VOX positively triggered.

If you use a program with a positive PTT output, I would use that  
(through an optoisolator) instead of VOX -- then you can run even  
lower audio levels, which result in less distortion.

Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901