[Elecraft] Baluns - give me a kit!

[George, W5YR]

Jerry, let me mention one aspect of baluns that may be of interest and help
in your understanding.

From your note, I gather that you are viewing a balun primarily as an
impedance transformer - something that will get an arbitrary antenna
impedance "close to the 50-ohm impedance that the K1/K2 want to see."

I think that this viewpoint only leads to more confusion.

Above all, a balun as commonly used with amateur antennas has only one
function: convert a balanced load to an unbalanced load for the connection
of a coax feedline or unbalanced network; or vice versa. When used at the
feedpoint of an antenna, its function is to block common-mode current
flowing on the outer braid of the coax.

The fact that some baluns can be constructed to *also* effect a
transformer-like action is incidental to the main function. The fact of the
matter is that seeking other than a 1:1 function almost always introduces
the complications and inefficiencies for which baluns are noted.

In order to effectively transform impedances, either an appropriate
transformer, an efficient impedance-transforming network, or a fortuitous
feedline length is required. A balun is none of these. 

The problem with N:1 baluns is that their transformer action becomes
heavily dependent upon the actual load they have as compared to their
design load. In the real world, antennas seldom present the theoretical
load for which they are designed. As a result, most baluns fail to function
as efficiently - both in terms of power loss and in eliminating common-mode
current - as they could if always properly loaded. This is particularly
true in the case of the 4:1 baluns typically used to provide a balanced
output from unbalanced T-network tuners.

So, the best solution that I have found, and many others echo this, is to
use 1:1 current baluns - either a coil of coax, or beads on coax (W2DU
balun) or parallel wire or coax wound around a toroidal core, depending
upon power levels and circumstances. Then use a transmatch or "antenna
tuner" to accomplish whatever impedance transformation is required. This
allows each component to do its job properly without being hampered by the
effects not prevented by the other.

I suggest that you start thinking of baluns in these terms and see if some
of the confusion is not cleared away. Roy Lewallen, W7EL, published the
classic article on baluns in the first Antenna Compendium published by
ARRL. It is required reading for anyone working with antennas. Equally
required is Walt Maxwell's article in the March 1983 QST.

73/72/oo, George W5YR - the Yellow Rose of Texas         
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe   
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771 I-LINK 11735
Icom IC-756PRO #02121  Kachina 505 DSP  #91900556  Icom IC-765 #02437


k6iii@juno.com wrote:
> 
> Eric/Wayne,
> 
> Baluns are a bit of a mystery to me... I'm pretty simple minded, now, but
> know there is a need for 4:1 and even 6:1 baluns (and others) with these
> QRP rigs. I see articles on making these, but the parts are usually not
> readily available. If Radio Shack (Tandy) has the parts please let me
> know what to get (i.e. RS part number, etc...). Sure, the KAT1 or KAT2
> auto antenna tuners will probably match any antenna I string up, but
> wouldn't it be better to at least get close to the 50-ohm impedance that
> the K1/K2 want to see? Maybe I'm missing something here, but...
> 
> It seems to me it would simple thing to market a do-it-yourself balun
> kit. I suspect Elecraft has all the parts and could kit up a core with
> some wire, maybe a box and a couple of connectors along with some
> instruction sheet on how to wind various baluns for QRP (use with K1's
> and K2's). Why not include a discusson in these instruction sheet about
> baluns and when you need to use them, along with a few simple wire
> antenna examples, etc...
> 
> I would imagine that you would sell quite a few of these balun kits.
> 
> (Reflector readers are encouraged to post what you have done, how to, web
> references, pictures, RS part numbes, etc...)