[Elecraft] Balun inside K2

[Charles Greene]

Hi John and All,

Earlier I had some discussions with Wayne about putting a balun inside the 
K2 and using the two holes in the back of the K2 for output connectors, but 
it ended up with us both agreeing that it was better to put it 
outside.  Wayne is still trying to figure out what to do with the two holes 
in the back of the K2.  I agree that you need a large core(s) to build a 
successful Voltage balun.  See page 34 of Sevick's book, "Building and 
Using Baluns and Ununs"  He describes an excellent balun, good for the 
legal limit using 21 turns on two T400-2 cores.  There's a reason for 
this.  The -2 material makes the best voltage balun, but you need a lot of 
core material to get adequate inductance.  I have been unsuccessful 
building a low power >100 watts 4:1 voltage balun.  Using cores from 
F114-43 to T187-2, if I use turns to get enough inductance for good 
performance on 160 meters, the high frequency performance suffers.  Typical 
performance is 1.8 MHz through 19 MHz, or 3.5 MHz through 30 MHz.  I am 
using same the criteria Sevick uses to define good performance which is 
basically a reasonable SWR into a balanced 200 ohm load.  I don't know 
about the LDG kit.  However, I have built many good performance 4:1 and 1:1 
current baluns.  See: http://www.njqrp.org/balun/index.html for a low power 
4:1 current balun kit that has excellent performance, designed by yours 
truly.  Here again, I wouldn't try to put it in my K2.

At 10:31 AM 7/5/2002 +0100, John Crux wrote:
>I have built two LDG AT11 tuners. I would not like to try putting a
>half decent balun into either my K2 or into the standard LDG case, or
>even into the home brew case I used for the first AT11.
>I have made several 4:1 baluns. One was on a T-200 powdered iron core
>and I made it for use with my AT11 by a UK foundation licensee, at his
>legal limit of only 10 watts RF. It was marginal on 40m and useless on
>80m (not enough inductance ?)
>So I swapped it for the humongous ferrite core balun (SIX 2.4 inch
>ferrite cores) the partly assembled guts of which I found on the
>Dayton flea market. If Jerry Sevick (see below) is right this item
>will probably handle 20 kW. Small it is not. Maybe an overkill for
>10w. But it sure works down to 160m !
>
>Before trying to squeeze a tiny balun into either the K2 or the LDG,
>I suggest asking if your journey is really necessary. From the
>literature (mostly the article by Jerry Sevick W2FMI in CQ, November
>1993 page 50) its not trivial getting adequate performance, especially
>from a small enough-to-fit-the-space toroid.
>Greater flexibility (and efficiency) is probably achieved by using an
>external balun whenever you need one. Cut your losses. There is a CWS
>ByteMark kit with a 2.4 inch ferrite core that should do the trick. Or
>I'd use a large powdered iron core, like a T-300D. Small is not always
>beautiful ..
>P.S. Wayne & Eric - assuming the KAT-100 will be designed to fit into
>the EC-2, there should be room for a nice BIG balun, if anyone wants
>one.
>John G3JAG
>K2 #609 into a few feet of RG-8, a Centaur balun (2 stacked ferrite
>cores) and lots of ladderline. Over 250 countries worked with a 40m
>dipole.




73, Chas, W1CG