[Elecraft] Re: KAT100 with Ladder Line

[Ron D'Eau Claire]

Nothing bad happens if you leave the balun out, Peter!

Sometimes we over-complicate things. A balun is a good example. All that's
needed to produce a balanced "feed" is a length of transmission line (1/4
wave or so) and a balanced load. If you have those things, it doesn't matter
whether the output from the rig is "single ended" or "balanced", the
currents at the balanced load, such as the center of a dipole, will be
balanced. 

All a "balun" does is wind up that feed line in a smaller, tidier package so
the currents at the rig end of the feed line are also balanced. That helps
keep feeder radiation and pickup at an absolute minimum, since open wire
feed lines depend upon balanced out-of-phase currents in the wires to
produce opposing RF fields that "cancel" each other. But very often it's
quite unimportant to have that balance at the rig. 

The un-importance of balance is shown in popular antennas like the G5RV,
which do not offer balanced feed no matter how they are fed. Being off
center, the feeder currents are always out of balance. They work quite well.
Indeed, the vertical radiation from the feeder is thought to be a part of
their effectiveness. The same is true of the modern open wire fed version of
the Windom.  

It seems that today a balun is most likely to be used to change the
impedance seen at the transmitter from something unknown to something else
unknown that the automatic matching network (ATU) can handle better. As
others observed, that's exactly the same as changing the length of the feed
line or antenna a bit. Adding a balun is usually more convenient than
changing the length of the antenna or feed line, but it adds to losses in
the system. How much is unknown. It can be a little or a lot and will change
with frequency. On-air tests are meaningless to evaluate the effect since a
few milliwatts can make it around the world at times and result in a nice
signal report on almost any frequency in the HF spectrum. It's easy to throw
away 50%, 75% or even more of the transmitter's power in losses and be
completely unable to detect it by evaluating how easy or hard it is to make
on-air contacts. 

One important issue to remember is that a passive device is *not* a lossless
device. Passive devices, like baluns, all have losses. 

Ron AC7AC


-----Original Message-----

Please, I'd like some more discussion of this question.  I've seen  
before that baluns on ladder line can be lossy, but I'm not about to  
get a balanced tuner, so it doesn't really help.  What happens if you  
connect the balanced line directly to the KAT100?  Or, in my case, to  
the KAT2?  I haven't had any problems so far -- maybe low power makes  
a big difference, or maybe I've just had antennas which were  
reasonable in some way.  I gather it's possible to get unpleasant  
currents on the case, mic, or paddle.  Is that exactly the condition  
in which the balun will be lossy?  Does connecting the ground screw  
on the KAT2 (or the one on the balun?) alleviate the common mode  
current problems?

	Peter N8MHD
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