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

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

Tom Coates wrote:
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?

As with stubs, it is frequency dependent and therefore is
limited to a single band. One advantage of a toroid-based
transmission line transformer is that it is broad-banded
often covering a 10:1 frequency range. If you confine it's
use to 20m, the "old design" should work well enough.
--
73, Cecil http://www.qsl.net/w5dxp

"Tom Coates" wrote in message
news
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

Hi Tom

If you are interested, I have about 20 new ferrite toroids that arent
marked. I wouldnt mind constructing a couple bifilar, 4:1 baluns and
connecting them back to bact for loss measurement at 14 MHz. If the
prototype works well enough, I could easily measure them at other
frequencies from about 5 MHz to 450 MHz.
The cores are 1.9 inch OD and 1.4 inch ID and 3/8th thick. I'd expect
one toroid to be adequate for power levels around 20 watts. That could
probably be estimated after the loss is measured.

So, if you are interested, I'll give you a couple cores after I make some
measurements on a prototype.

I'd do a little research on web published information before building the
prototypes.

I have build alot of baluns for higher frequencies, but I cant make power
on any band.

Jerry

Again, I am not interested in selling. HAM stuff is my fun time.

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

Hi Tom

I use a Q section of 100 ohm "coax" (2x 50r cables side by side with
shields joined at each end) on my 20m single loop quad (about 140 ohms
modeled) I went for the higher load Z (200r) because I wanted a higher
SWR b/w and the possibility that it might work on odd multiples (not
that there is an amateur band on 42MHz! - Thinking about a 30m version)

It seems to work well but it isnt as if I have made any serious
comparisons. Its 2:1 SWR b/w is something between about 13.5 and 15MHz.

All you need is coax and allowance for velocity factor!

Dont know about the balance/unbalance side of things so much. I was
getting some shack radiation that a choke balun (turns of coax on an air
core) where the feed met the Q didnt seem to help much. The antenna
itself is only 8-10m from the shack anyway.

I can send you the modeled details if you like.

Cheers Bob VK2YQA

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.

On Sat, 29 Jul 2006 23:40:55 -0400, "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.

You asked for a balun for one band.

Your proposed solution works fine. It is a narrowband solution, which
is fine if you only want to work 20m.

Very widely used on VHF Yagis which are narrowband applications.

Some have written that the loss in feed to one side of the balanced
load (~0.2dB for RG213 at 20m) causes significant pattern distortion.
However, most baluns are not perfectly balanced.

Owen
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