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

[Edward R. Cole]

Joe, W4TV, wrote:

The difficulty in dealing with a computer interface for the KX3 is
the last of a fixed level audio output and the need to share audio
with the operator headphones/speaker.  Levels for computer decoding
and operator comfort are not always the same <G> which means a
buffer/splitter amplifier, external speakers with separate volume
control and headphone jack or some other "extra box".
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I rarely listen to the audio of digital signals since my brain cannot 
decode them, anyway.  With a 3.5mm phone plug inserted the internal 
speaker is disconnected so I suppose you are using either headphones 
or ext. speaker.  No need to hear the signal so volume on KX3 is 
adequate to set proper level for digital sw.

But one could provide for separated audio to speaker/headphone and 
computer with audio amp and pot for level setting.  Final audio level 
is set with soundcard dialog box, anyway.  In my case I use an ext 
soundcard that has pots for line-in level.

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Regarding serial connections to the computer this is easily handled 
by either a full RS-232 cable if you have RS-232 on your computer or 
by using a USB/RS-232 conversion cable (like what comes with the 
K3).  One then connects DB-9 pins 2,3 for RXD and TXD to a cable to 
plug into the ACC-1 jack, and take off pins 4, 7, 5 to split out RTS, 
DTR and ground to supply PTT and CW keying, per one's needs.

To provide fullest versatility I would provide both a DB9 serial port 
for full serial connection and the 3.5mm mini-phone jack for the 
KXUSB cable (RXD, TXD) for those not requiring RTS/DTR controls. One 
just uses whichever cable is suitable to their sw needs.  If you use 
the KX3 VOX for audio-sensed PTT there is no need for any ancillary 
ckt.  If you need hard switched PTT then use RTS/DTR per your sw.

Audio interface should use isolation transformers, and the mic audio 
requires a pot for setting proper modulation level (using the ALC 
display).  The four contact mic mini-plug is probably the hardest 
item to come up with.

Such would satisfy all users, I believe (I do not use HRD or other 
control sw so perhaps they require addition controls?).




73, Ed - KL7UW, WD2XSH/45
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