Digital Mode Interface for the KX3 for WSJT modes

[W7GJ, Lance]

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: [phone]
QTH: DN27ub
URL: http://www.bigskyspaces.com/w7gj
Windows Messenger: [hidden email]
Skype: lanceW7GJ
2m DXCC #11/6m DXCC #815

Interested in 6m EME?  Ask me about subscribing to the Magic Band EME
email group, or just fill in the request box at the bottom of my web
page (above)!

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[Jim Brown-10]

On 7/11/2012 9:48 AM, Lance Collister, W7GJ wrote:
> 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?

Hi Lance,

A clarification.  The 4.7K/470 ohm network is a simple 20dB pad (voltage
divider), and almost any values in this range and with this ratio will
work just fine. Use what's in your junk box.

Hum and buzz are caused by leakage currents from the AC mains, which
create IR drops in the green wires and other conductors that connect
equipment to "ground." Those IR drops are DIFFERENT for each piece of
gear because the resistance of the grounding path is different, and,
because the connection between gear is unbalanced (that is, one side is
connected to the chassis at each end), that DIFFERENCE is added to the
signal.  The leakage currents are 60 Hz and the harmonics of 60 Hz, and
they sound more like buzz (the harmonics) that hum (pure 60 Hz).

The solution is VERY simple, but because we have for decades used the
wrong words -- "ground loop" -- to describe the problem, is almost
always overlooked.

That simple solution comes in two steps. 1) Get all power for
interconnected equipment from the same AC outlet, or from outlets that
share the same "green wire" (that is, they are in the same steel
backbox), or from outlets whose green wires are bonded together by short
fat copper.  2) Bond from chassis to chassis of all interconnected
equipment with short, fat copper.

Be sure to complete all this by the long established good engineering
practice for safety and lightning protection -- bond from that
collection of chassis connections to everything else in your building
that's grounded.  That tends to help minimize the presence of leakage
current on the wiring of our equipment.

73, Jim K9YC

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[W7GJ, Lance]

Thanks for all the comments and suggestions.  I will continue to explore the
possibility of an ultra-compact solution by just breaking out cables from a DB9
connector.  However, in the interest of time, my first interface will use the
RIGblaster Plug & Play unit from West Mountain Radio.

This compact unit provides a USB interface to the computer, plus completely isolated
audio lines for input and output and  isolated RTS (for PTT) and DTR (for true CW)
keying from the computer. This interface also already includes a stereo jack for CI-V
rig control, that appears to be directly compatible with the ACC1 jack on the KX3, so
that is one less breakout connection I need to build!  It also already has a separate
jack for a speaker, so I can listen with headphones at the same time as the
computer.  This is especially handy when copying CW and still needing the audio to be
fed to the computer so it can display the spectrum with a waterfall program such as
Spectran.

I have already ordered a couple inexpensive female DIN connectors from Digikey to
connect with the output "ACC PLUG" line from the RIGblaster Plug & Play unit, and
from there I will simply run a line to the KX3 Headphone Jack (for the audio out) and
another shielded stereo cable to the KX3 4 pin microphone plug (for audio and PTT
into the KX3).   I will use the KX3 ACC2 jack to key my amplifier.

I know there are others on this list who are interested in operating digital modes
with an RTS line advance PTT keying capability, and I will provide photos and results
as soon as I have everything completely assembled and tested.

VY 73, Lance


On 7/11/2012 4:48 PM, Lance Collister, W7GJ wrote:

> 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: [phone]
QTH: DN27ub
URL: http://www.bigskyspaces.com/w7gj
Windows Messenger: [hidden email]
Skype: lanceW7GJ
2m DXCC #11/6m DXCC #815

Interested in 6m EME?  Ask me about subscribing to the Magic Band EME
email group, or just fill in the request box at the bottom of my web
page (above)!

______________________________________________________________
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Help: http://mailman.qth.net/mmfaq.htm
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