On Tue, 10 Jan 2006 01:31:51 -0500, Scott in Baltimore
wrote:

+The amount of inductance is determined by the number of coils
+and how closely spaced together they are. There is not going
+to be much difference in three feet. Maybe wrapping the coil
+with aluminum foil would help to increase the coupling on
+the coil to increase the inductance.
+

If you want to increase the inductance wrapping aluminum foil on the
outside is not going to produce adequate results. Instead, place
ferrite material within the form so that it sits inside the windings.
If you want to decrease the inductance use aluminum inside the
windings.

This is how tunable inductors work.

+The inductance in the coil only affects the outside of the shield,
+the exact place you don't want current flowing. It won't affect
+the signals inside the coax.
****

Coiling coax up to form a choke balun places an impedance inline with
the outer conductor of the coax. It is this impedance that limits or
"blocks" unwanted current from flowing down the outer shield of the
coax. Coiled baluns should be located as close to the feed as
possible.

james