Bob Miller wrote:
For any given frequency, would that 8 ohms or 4000 ohms be decided by
the length of the dipole or the length of the ladderline, or both?

Both. For instance the resonant impedance of a G5RV on the lower
part of 80m is usually about 8 ohms. If the feedline for a one
wavelength dipole is 1/2WL, the impedance will be about 4000 ohms.
The feedline impedance seen by your tuner is somewhat unpredictable
and EZNEC can tell you what ballpark impedance to expect. EZNEC
has saved me an enormous amount of time - 10 minutes of simulation
Vs 10 hours of antenna erection time.
--
73, Cecil http://www.qsl.net/w5dxp