[Elecraft] Balun for KAT2

Mon Jan 14 07:46:00 2002

Thanks.  It sounds like the summary is:

Regarding the use of toroidal baluns to connect a balanced transmission line
to the (unbalanced) output of the KAT2:

1) Toroidal baluns are commonly used for this purpose.  They do exhibit
losses with high SWRs, but usually not enough to noticeably affect antenna
efficiency.

2) Under high SWR and relatively high power, a toroidal balun can easily
overheat.  To avoid this, use a beefy toroid, avoid placing it at a current
node, and don't use high power <g>.

----- Original Message -----
From: "Charles Greene" <[email protected]>
To: <[email protected]>
Cc: "Jonathan Taylor, K1RFD" <[email protected]>; <[email protected]>
Sent: Monday, January 14, 2002 6:20 AM
Subject: RE: [Elecraft] Balun for KAT2

At 11:20 AM 1/13/2002 -0800, Ron D' Eau Claire wrote:

Ron and All.

I'd just like to emphasize a couple points Ron made.  There are two aspects
of losses.  One is how it affects your antenna system.  The losses of a
typical balun operated into a SWR of 5:1 or less are insignificant compared
to the other losses in your antenna system, so don't worry about
that.  However, a loss of 3% if you are running a KW is 30 watts, enough to
burn up all but the larger baluns.  I guess the moral is to use a balun
rated for the power you are going to use, and don't operate it at a current
node (high voltage point) in an open wire feed line.

>After I posted the message about using a couple of small light bulbs for
>checking the 'balance' at the output of a balun, Chas, W1CG, dropped me a
>note that said:
>
>"I have made some and run some efficiency
>tests.  The 13 T on a FT114-43 core is 97% efficient into a balanced 200
>ohm load, and is 90% efficient into a 5:1 SWR.  They are small and use high
>permeability ferrite to get enough inductance to operate at 1.8 mHz with a
>5:1 SWR, (110 uhy).  A lower loss ferrite or powered iron core would have
>lower losses.  The loss of 3% is 0.13 dB, and the loss of 10% is .45 dB.  I
>use one on a my W3EDP antenna which runs 5:1 SWR on some bands, at 100
>watts.  The loss of a 1:1 using beads or a coax coil is less lossy."
>
>Charles has written about that before, and I hope he doesn't mind my
>repeating it here because it is good stuff.
>
>Just because a balun CAN be inefficient doesn't mean that it IS
inefficient.
>I have successfully used them in many conditions. My warning was only that
>they CAN be power eaters and that it is not always as obvious that's what's
>happening. One time I did get a warning when I smelled a funny odor running
>10 watts on 40 meters. It was the plastic on a banana plug connector to my
>feedline melting from the high r-f voltage at that point! The balun - one
>out of a "300 watt" MFJ tuner - was also hot.
>
>Since then I've found that, most often, the balance to the feeders goes to
>pot when the balun is pushed too hard. That's why I suggested the little
>light bulb test as one way to get a clue about what is happening.
>
>But, as Chas has documented from his tests, you can expect a decent balun
to
>behave very well much (perhaps most) of the time as well.
>
>Ron AC7AC
>K2 # 1289
>
>
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73, Chas, W1CG

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