[Elecraft] Digital Mode Interface for the KX3 for WSJT modes

[Lance Collister, W7GJ]

I am still waiting for my KX3, but I imagine with over 600 of them out in the field, 
SOMEBODY must have experimented with an interface for running WSJT modes.  I will 
need to build up the custom interface cables as soon as my KX3 eventually arrives, 
and I won't have much time left to troubleshoot or re-do things.  So I sure would 
appreciate any suggestions or guidance anyone with experience on their KX3 may be 
able to provide.  I am HOPING there might be some way to simply use resistors to pad 
down the computer LINE OUT and isolate it enough to work with the KX3 MIC INPUT.

I realize I will have to break out several of the serial port lines from the computer 
DB9 and connect them to various jacks on the KX3.  The TX (pin 3) and RX (pin 2) 
obviously must be connected to the ACC1 plug ring and tip, respectively.  Do I just 
connect the sleeve of the ACC1 to both the SIGNAL GND (pin 5) AND the SHELL 
ground/cable shield?

For the ACC2 plug, I am planning to use the RING to turn on my amplifier, and the TIP 
will be connected to RTS (pin 7) of the computer serial port.  Wayne had mentioned 
before that there should be a 2200 ohm resistor between the tip and the RTS line 
connection.  I assume the sleeve of the ACC2 is connected to both SIGNAL GND (pin 5) 
AND the SHELL ground/cable shield?

Of course, the KX3 HEADPHONE line will go directly into the computer LINE IN - no 
problem ;-)

I am planning to connect the computer LINE OUT to the tip and sleeve of the KX3 MIC 
jack.  However, in K9YC's interface manual, he suggests, putting a 4700 ohm resistor 
in series with the tip, and putting a 470 ohm resistor from tip to sleeve.  Has 
anyone tried this yet on digital modes with the KX3?  Does this provide enough 
isolation and prevent hum?

I see in the manual that a power cable with a 2.1-mm plug is supplied, so I can use 
that when I receive my KX3.

I would greatly appreciate input from anyone who has already "broken trail" on 
building these KX3 interfaces ;-)  MNI TNX and VY 73, Lance

-- 
Lance Collister, W7GJ
(ex WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8, E51SIX, 3D2LR, 5W0GJ)
P.O. Box 73
Frenchtown, MT   59834-0073
USA
TEL: (406) 626-5728
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URL: http://www.bigskyspaces.com/w7gj
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