[Elecraft] K2/Writelog computer interface

[Jim Brown]

On Wed, 11 May 2005 14:11:24 -0400, Andy Bullington wrote:

>Any info would be much appreciated. 

Writelog keys the K2 VERY nicely using their serial port method. 
To make it work, you need to make a very simple interface. 

1) Pin 4 of the serial cable (from the computer) thru a 1K 
resistor to the base of a generic NPN (I use a 2N4123 because I 
have a lot of them, but any general purpose NPN will work). 

2) Collector of the transistor to both sides of the key jack 
through diodes (just as you would do with a straight key, per the 
manual).

3) Emitter of the transistor to the shell of the key jack. 

You can now use both your paddle and the computer to key the 
radio. Very nice in a contest. 

Several measures will eliminate the RF feedback that often results 
if you use the standard K2 serial cable. What I've described below 
is good for at least 1 kW into a long wire antenna running right 
next to the rig!

1) Use shielded twisted-pair cable, NOT the parallel conductor 
cable that comes with (or at least did come with) the standard K2 
serial interface. Braid shield is better if you can find it. Use 
one twisted pair for each signal line. That is, one pair for pin 
2, one pair for pin 3, and one pair for pin 4. 

2) Connect the shield to the shell of the DB9 on each end, NOT to 
pin 5 of the DB9. I don't make any connection to the pin 5's -- I 
connect signal returns to the shell of the DB9's too. 



Jim Brown  K9YC