Gene Fuller wrote:
So, the "point" is ??????

Given a 100 foot long helical transmission line at
4 MHz terminated in its characteristic impedance.
The VF is easily measured. This is a slow-wave
configuration.

Change the length to 50 feet terminated in its
characteristic impedance. Why would the characteristic
impedance change? Why would the VF change?

The coil diameter is 0.5 feet. The coil diameter ratio
to wavelength is 0.002. The turns per foot is 48.
The turns per wavelength is about 11800. Reading from
Fig.1 in the Corum article gives a VF of about 0.02.
Why would that change appreciably with frequency?
--
73, Cecil http://www.w5dxp.com