[Elecraft] KAT100 Question

[Charles Greene]

Hi,

Not necessarily.  The 100 watt 4:1 current balun I designed and which is 
offered as a kit at:
http://www.njqrp.org/ by the NJQRP club operates without excessive heating 
or excessive loss (the loss is about 4%, 4 watts in 100 watts) and it 
doesn't get hot into a 5:1 or less SWR.  It was specifically designed for 
this application.  You just have to exercise due diligence and not put it 
at a current node.  The documentation that comes with the kit explains all 
of this.  I also have run a Radio Works 2KW 4:1 current balun under the 
same conditions and it doesn't get hot or lose much power either.

I think it's a good application of a balun, and use such 
myself.  Typically, there is a balun inside antenna tuners for use with 
open wire lines.  Sevick devoted an entire chapter to baluns for antenna 
tuners, in his "Building and Using Baluns and Ununs."  He starts with the 
balun used by McCoy in his original Transmatch, and then proceeds to 
improve the design for one that will take maximum power.  However, as he 
says, you can't put the balun at the point in the transmission line where 
the voltage is at a maximum and the current is at a minimum.  How do you 
know?  Try it, and if your balun gets hot to the touch at low power, trim 
your transmission line and try again.

At 11:06 AM 12/1/2002 -0500, Brian Machesney wrote:
>If you're going to use a "balun" as a "transformer," be prepared to
>accept heating of and consequent power loss in the balun core.
>Traditional, transmission-ine baluns are designed to be operated
>into a specific set of impendances. Operation into other loads upsets
>the current balance, causing magnetic flux to develop in the core;
>see Sevick's book for an excellent treatment of this subject.
>
>I have not investigated whether "oversizing" the cores (vs. the
>power level the "traditional" balun should tolerate) would help by
>ameliorating the deleterious effects of heating.
>
>Brian Machesney, K1LI
>
>reference text:
>
>"...if I use ladder line and a balun with a short piece of coax into the
>shack to a wide range tuner preferably a wide-range T-network tuner,
>I can work the WARC bands as well."


73, Chas, W1CG
K2 #462