Cecil Moore wrote:
On Jun 20, 8:01 am, Buck wrote:
Does anyone know where I might find that formula?

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.

Dave K8MN

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