[Elecraft] KX3 cables for microHAM

[Joe Subich, W4TV]

I have placed drawings for DB15-EL-KX3 (USB II, USB III, Digikeyer,
and Digikeyer II) and DB37-EL-KX3 (microKEYER, microKEYER II, MK2R+)
cables in the files area of the microHAM list on Yahoo -
http://groups.yahoo.com/group/microHAM - and at:
   http://www.microham-usa.com/Downloads/DB37-EL-KX3.pdf
   http://www.microham-usa.com/Downloads/DB15-EL-KX3.pdf

Due performance issues in paralleling headphones or (powered) speakers
with the input of the microHAM sound cards and potential hearing damage
from excess headphone levels, the microHAM factory have declined to
produce these cables.  Individual users may, of course, build from
these designs for their own use but the designs may not be duplicated
commercially without permission.

The KX3 headphone output is limited to substantially less than 100 mW
if the audio to remain undistorted (absolutely essential for digital
decoding).  While the "sound card" in the microHAM interfaces has a
relatively high input impedance and a low noise, high gain preamplifier
with transformer isolation that would have no problems working from the
headphone output by itself, paralleling headphones or powered speakers
with unknown impedance can certainly cause issues of loading as well as
hum and/or RF pick-up.

Best results will be achieved by using powered speakers and connecting
headphones to the speakers (many have headphone jacks).  This way the
KX3 may be set for undistorted output and listening levels can be set
with the volume control on the speaker amplifier.  If speakers are not
appropriate due to weight/space considerations, use headphones with an
impedance of at least 32 Ohms (the Yamaha CM-500 is 120 Ohms) to avoid
loading or loss in the KX3's output.

73,

   ... Joe Subich, W4TV
       microHAM America
       http://www.microHAM-USA.com
       http://groups.yahoo.com/group/microHAM

       support e-mail:  support at microHAM.com