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