Dave Heil wrote:
Cecil Moore wrote:
How about a rule of thumb? Using a 2 liter pop bottle, make the number
of turns equal to the wavelength in meters. That will optimize for a
specific wavelength but will render it not very useful for any shorter
wavelengths, e.g. 20 turns is too many for 10m.

So it is your "rule of thumb" that 160 turns would be used for 160m?
I don't think so, Cecil. Six or eight turns on such a form should work
fine for 20-10m.

For maximum impedance, i.e. optimized for a single frequency,
the ugly balun would be 1/4WL self-resonant. I think you will
find that, for HF frequencies, the number of turns of RG-213
on a 4 inch coil form is in the ballpark of the wavelength in
meters. Thus, close to ten turns would be optimum for 10m.
Such a balun, although it would work, would not be optimized
for 20m as the impedance would be maximum around 10m.
--
73, Cecil http://www.w5dxp.com

On Wed, 20 Jun 2007 11:31:19 -0700, John Smith I
wrote:

Buck wrote:

[stuff]

Or, you may just want to use an, apparently, tried and accepted design:

http://www.hamuniverse.com/balun.html

Regards,
JS

That's close. they say it is good for 160-10 meters, but what if I
only want one for 10 meters or just 2 meters? Is there a rule of
thumb to build x turns at x diameter.

--
73 for now
Buck, N4PGW

www.lumpuckeroo.com

"Small - broadband - efficient: pick any two."

Buck wrote:

...
That's close. they say it is good for 160-10 meters, but what if I
only want one for 10 meters or just 2 meters? Is there a rule of
thumb to build x turns at x diameter.


Buck:

Personally, I just use a big toroid with sufficient turns of coax looped
through it (if using large diameter coax, I stack two or more toroids.)
Ferrite beads are another path one can utilize ...

I consider a +jX of 10X the coax impedance at the freq(s) in question
sufficient (and yes, I know some get by with 5X, and 5X is much more
"handleable" at 160m)--it is just a glorified choke; examine all the
formulas, equations, tables and charts you wish, and complete your
experiments--you will only reach this same conclusion. Since you are
only choking the currents on the outside of the braid, too much +jX is
not a real critical consideration--having enough is ...

Unfortunately, no black magic is used in its construction, but still,
and even at my age, I am fond of fairy-tales :-(

Others who have actually used the air core chokes of coax would be,
better, able to provide you with real world data, no doubt.

With the junk drawer of toroids I purchased decades ago--I have a
lifetime supply. (Indeed, I may need another lifetime to make full use
of 'em!)

Regards,
JS