Tom Coates wrote:

I'm seeking a 4:1 balun design that could handle 10 watts efficiently on
20M and would be easy to reproduce without purchasing special ferrite cores,
etc.

There's an old design that puts an electrical half wave of coax between the
two connectors on the balanced side.

What drawbacks does this old design have compared with more modern ones?
Suggestions would be appreciated.

Tom, N3IJ

There is an air core balun described in Hints and Kinks 12th Edition
12 trifilar turns (three wires of identical length) of #12 or 14 ecw
close wounds on a 1 inch od form. It's a 1:1, but I would think that
you could try experimenting and produce a 4:1 without too much trouble.

The coax baluns can be heavy and cumbersome -- a simple ferrite bar
could be used in lieu of a core. Cores are readily available at most
radio wholsalers. For 20 watts you could build a very small but
effective balun,

This does not fully answer your request but may put you on the
right track. You might find some in the newer antenna books.

Irv VE6BP

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Irv Finkleman,
Grampa/Ex-Navy/Old Fart/Ham Radio VE6BP
Calgary, Alberta, Canada

Irv Finkleman wrote:

REDACTED

There is an air core balun described in Hints and Kinks 12th Edition
12 trifilar turns (three wires of identical length) of #12 or 14 ecw
close wounds on a 1 inch od form. It's a 1:1, but I would think that
you could try experimenting and produce a 4:1 without too much trouble.

REDACTED

My original balun from 30+ years ago was an airwound balun, commercially
manufactured by B&W. It handled 250 watts AM from 80 through 10 meters.

If I recall correctly it was two bifilar wound coils, close spaced, about 10
inches long with the series parallel jumpers for 4:1 impedance ratio.

/s/ DD W1MCE