On Wed, 24 Jan 2018 08:33:55 -0800, johndusek3 wrote:

+AD4 My question is - do I need to use the full 100 feet of feed-line to keep
+AD4 the antenna resonant, or can I shorten the feed line to fit my space
+AD4 without impacting antenna resonance?

The short answer is -- shorten the lead in to whatever is convenient and
you'll be fine.

That's assuming that the radio end of the lead in matches the impedance
of the coax. If the radios have coax connectors they're probably close
enough.

Older boatanchor radios, say from before 1950, commonly had higher
impedance antenna inputs, designed for end fed wire antennas. If you
have such a radio, you might need a balun or matching unit for best
performance. But a mismatch won't damage anything.