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.

Inductors are the exact electrical opposite of capacitors.

Capacitors block DC and pass AC. They have decreasing reactance
to higher frequencies. Current leads the voltage by 90 degrees.

Inductors block AC and pass DC. They have increasing reactance
to higher frequencies. Current lags the voltage by 90 degrees.

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.