[Elecraft] KRC2 and KX3

[Vic DiCiccio]

When Eric VA7DZ, Fred KE7X and I were all experimenting with KRC2s for 
our K3s, I also connected mine to the KX3 with the help of Jack Brindle, 
KRC2 expert.

Here's what I did to the KRC2 to make it work in between the KX3 and the 
computer:

1.  Set KX3 menu item RS232 to 19200b.  Set the appropriate software on 
the computer to 19,200 baud.

2.  Use only the following jumpers in the KRC2:  W3, W8, W9, W10, W21, 
W22, W23.

3.  Make a special jumper wire to go from the RS-232 connector side of 
W11, to the RS-232 connector side of W20.  This carries the DTR signal 
between the two RS-232 connectors without actually bringing it into the 
KRC2 circuit.  It's voltage is incompatible with the KRC2, but it needs 
to be "carried through" if you intend to break out the DTR signal to, 
say, key the KRC2 with a transistor (or perhaps use DTR for PTT, or you 
could figure out the RTS pin on the RS-232 if you prefer).

The circuit diagram in the KRC2 assembly and operating instructions 
booklet is very useful to help to understand the jumpers.  Normally, for 
a K3, you'd use W16 to enable the Auxbus in the KRC2.  W3 tells it to 
use the serial port, not the Auxbus. W8 sets it to 19,200 baud.  W9 and 
W10 carry the pin 2 and pin 3 data for RS-232.

As Jack said, it's important to only connect pins 2, 3, (both data) and 
5 (ground) to the KRC2 circuit because the other pins of RS-232 are 
electrically incompatible with the KRC2.