Cecil Moore wrote:
Based on some calculations I did today, I am offering
an original rule of thumb (as far as I know). Regarding
a coax choke, when deciding how many turns of coax to put
on a 2 liter pop bottle at two turns per inch, one needs
to avoid the self-resonant frequency. So don't put more
turns on the choke than the number of meters in a wavelength,
e.g. no more than 20 turns on 20m, no more than 6 turns on
6m. Backup calculations will be published on my web page.
--
73, Cecil http://www.qsl.net/w5dxp

20 Turns is way too much for 20 through to 10.

http://www.k1ttt.net/technote/airbalun.html

Some actual measurements with a Network Analyzer. It shows 6 turns is
enough for 20 through to 10.